Volume.5. Study of Hydraulic Circuits

Q. S. Khan B. E. (Mech.)

Tanveer Publications, Mumbai - 78

CONTENTS Hydraulic Circuit

10.1 What is circuit? circuit? 10.2 Classification of hydraulic circuit. 10.3 Selection of different different circuit for some function. 10.4 Selection of working pressure. 10.5 Pressure Pre ssure in hydraulic hydraulic Ststem. 10.6 Calculation Calculation of heat generation in hydrauli hydraulicc Ststem. Sts tem. 10.7 Sequence S equence and cycle diagram. diagram. 10.8 Circuit diagram ffor or modular type power pack. 10.9 Use of filter filter in hydraulic circuit. 10.10 What is pumpin pumping g unit and power pack unit? 10.11 Pressure control circuit. 10.12 Pressure P ressure holding circuit. circuit. 10.13 Decompression Deco mpression circuit. circuit. 10.14 Hydraulic Hydr aulic circuit circuit with back pressure. 10.15 10.1 5 Back Pressur P ressuree in a hydraulic hydraulic cylinder. cylinder. 10.16 Hydraulic Hydraulic circuit using sequence valve. va lve. 10.17 Direction contro controll circuit. circuit. 10.18 Regeneration Regenerat ion circuit. circuit. 10.19 Brake circuit. circuit. 10.20 Flow control contro l circuit. circuit. 10.21 Synchronisation Synchronisation circuit. 10.22 Circuit diagram of drill.

10.1to 10.62

Study of Hydraulic Circuit

What is circuit

10. Introduction to Hydraulic Circuit 10.1. What is Circuit? • The Hydraulic power is generated by pumps, and supplied to hydraulic hydraulic actuators. actuat ors. This hydraulic hydraulic power must must be controll controlled in in order to achi achieve eve the desired desired functi function. on. A hydraul hydraulic ic circui circuitt is basical basically ly designed to have effective effective control con trol over o ver this generated generat ed power. po wer. A hydraulic hydraulic circuit consists of fluid conductor such as steel pipe, hoses, and manifold manifold block to transfer fluid. fluid. It has valves to co control ntrol pressure, direction, direction, and and flow flow of hydrauli hydraulicc fluid. fluid. And hydrauli hydraulicc accessories accessories for better control of various parameter para meter and to have safety and long life of hydraulic hydraulic system.

In this chapter we will study various types of hydraulic circuit. Generally three types of controls contr ols we do over generat generated ed hydraulic hydraulic power. powe r. a) Direction control. b) Pressure Pressure control. control. c) Flow control contro l feature, and direction control contr ol valve is common common in almost all the hydraulic • Direction control circuits. • Pressure Pressu re control cont rol feature and safety sa fety valve valve is also also comm co mmon on in all the hydraulic system. In addition to main system pressure, some so me circuits circuits are specially specially designed designed to reduce pressure, pressure , to generate ge nerate back pressure, pressure, to have have diff differen erentt press pressure ure at diff differen erentt parts parts of the circui circuit. t. •

Some circuits are ar e exclusively exclusively designed to control contro l flow flow of o f hydraulic hydraulic fluid in in the system.

hydraulic circuit may have have all the three features in it. That is control contro l of direction of • A complex hydraulic fluid, fluid, and control co ntrol of o f its pressure and flow. flow. thoro ughly understand understa nd hydraulic circuit circuit and simplif simplify y its study, we will will classify classify various various types • To thoroughly of hydraulic hydraulic circuit in to various categories, categ ories, then t hen study each category categ ory in detail.

“Design and Manufacturing of Hydrauli Hydrauli c Presses.” Presses.” ©: Q.S. Khan Khan

10-1


Classification of Hydraulic Circuit

10.2 Classification of Hydraulic Circuit Hydraulic power system or hydraulic circuit circuit could co uld be divided divided in to two broad bro ad categories. categ ories. a) Closed-loop circuits:-

A close-loop close-loop hydraulic circuit has all the basic elements elements of hydraulic circuit, such as hydraulic pump, hydraulic valves to control direction, flow and pressure, hydraulic accessories etc. In addition to these component it also has a feed f eed back mechanism which continuously continuously monitors system output. It generates a signal which is proportional to output, then it compares it with input or command or reference signal. If the two matches, then there is no adjustment and the system continue to operate as programmed. If there is a difference between between the input command signal and the feed back signal, then the system has provision and mechanism to correct and adjust the output to match with the command requirement.

Feed-back Mechanism

CLOSE-LOOP CIRCUIT

An electro-hydraulic servo system is a feed back system which measures measures and corrects the output. b) Open loop circuit:-

In this type of of circuit, we do not not get feed back. An open-loop hydraulic circuit do have all the basic elements of hydraulic circuit but it does not have feed-back machenism. OPEN LOOP CIRCUIT

Open loop as well as closed-loop circuit could be further sub-divided into two categories. 1) Open circuit 2) Close circuit

M

In open circuit the fluid is sucked sucked from reservoir by pump. Fluid passes through hydraulic component and again exhausted to reservoir. Reservoir has excess quality of fluid then what is required r equired by hydraulic circuit. And quantity of fluid in hydraulic circuit could be changed without any restrictions. In close loop, reservoir is eliminated and suction of pump is connected to exhaust line of circuit. Hence a fixed quality of fluid keeps on circulating in hydraulic system.

OPEN CIRCUIT

Q M Q COLSE CIRCUIT

Majority of hydraulic systems are open circuit. Close circuit is used for sophisticated, highly accurate and compact machineries. Constant flow circuit and demand flow circuit:-

These two terms are also used for for hydraulic circuit. c

T

In constant flow circuit, full discharge dischar ge of pump always flows through the system and returns to reservoir, The volume of flow does not change in minimum minimum as well as in maximum pressure pressu re condition. While in demand demand flow circuit, the volume of fluid circulating circulat ing through circuit changes with demand or requireme r equirement nt of circuit. Volume of fluid could be reduced by using variable discharge pump or other type of hydraulic valves. • Most of the hydraulic systems are designed as per open loop and open circuit. Hence first we will study open circuit in detail. “Design and Manufacturing of Hydrauli Hydrauli c Presses.” Presses.” ©: Q.S. Khan Khan

Demand flow circuit variable with displacement pump

10-2



10.3 Selection of different circuit for same function Suppose a hydraulic cylinder of 35 ton capacity has to move a load for distance of 50 cm. Now said said circuit circuit could be made in many many ways ways . Four of them are as follow follow.. TYPE 2 TYPE 1

P P

M

M

TYPE 4

TYPE 3

M P

M

• In first first system system actuator moves moves with with same speed throughout throughout it’s it’s stroke. And And maxi maximum mum working working pressure pressure is availab available le from start of stroke, till till end of strokes. • In second second and fourth fourth system system,, actuator could could have have fast fast approach approach and return return speed speed and show show pressi pressing ng speed. speed. And And full full working working pressure pressure will will be availa availabl blee in last last slow slow pressin pressing g operation. operation. • In third third system system,, we can have high high speed speed as well as full full working working pressure pressure throughou throughoutt stroke. But accumulator accumulator takes some so me time time for charging. charging. It cannot give continuous high speed and pressure p ressure without charging, and some delay time. time. All the four system has their the ir unique advantage advantag e and disadvantage; d isadvantage; similarly similarly any hydraulic hydraulic circuit could be designed in many ways, hence knowing different types of vlaves and components, compo nents, their t heir functions their the ir cost and knowing kno wing basic requirement requirement of hydraulic machine is is must must before designing d esigning hydraulic system.


10-3



10.4 Selection of working working pressure pressure With the help of o f following following example, we w wil illl study the importance of o f working pressure pressu re while designing a hydraulic circuit. Examples: Suppo se we want to move a weight of 35 ton at the t he speed of 160 cm/mi cm/min., n., for a distance of • Suppose 50cm simplest hydraulic hydraulic circuit for said purpose, which consists of a motor, pump, relief • We select a simplest valve, direction control cont rol valve, hydraulic hydraulic cylinder cylinder and standard s tandard hydraulic hydraulic accessories. acces sories. Bill of Material

5

Sr.No.

1 2 3

Motor Pump Relief valve

4

Direction control valve

5 6 7

4

Name of components

Hydraulic cylinder Oil tank Standard accesories

1 3

To deliver oil To regulate pressure To control direction of cylinder Actuator Oil reservoir To maintain quality of oil and safety of system

M

P 7

2 6

Functions Prime mover

7 7

7

HYDRAULIC CIRCUIT DIAGRAM

pr essure 70, 200 and 350 35 0 kg/cm2 and find the capacity capa city of pump, valves • We will select three pressure and standard accessories to have 160 cm/min speed while moving 35 ton load at these pressures.V pressures.Various arious parameter parameter at 70kg/cm2 will be be as follow fo llow • Load = Cross-sectional area o f cylind cylinder er X working pressure W = D2 X 4 X P 35000 = D2 X 0.785 X 70 D = 25.238 cm Pump capacity = Cross-sectiona Cross- sectionall area of cylinder cylinder X speed Q = D2 X

4

X V

= (25.238)2 X

X 160 4 = 80001.25 cc per min. min. 80 litre litre per min.

Power of o f electric electric motor motor (kw) = =

PXQX100 612 X 

Where: W = Load (kg.) D = Inside diameter (cm) P = Working pressure (kg/cm2) V = Velocity of cylinder (cm/min) Q = Pump discharge (cm3/min) = System efficiency in percentage

70X80X100 = 11.4 612 X 80

• Hence at 70kg/c2 working wo rking pressure ID of cycle will will be 25.238cm, 25.238 cm, pump capacity will be be 80 LPM, and power of electric motor will be11.4 kw. “Design and Manufacturing of Hydrauli Hydrauli c Presses.” Presses.” ©: Q.S. Khan Khan

10-4



•

For 200kg/cm2 working wor king pressure, inside diameter diameter of cylinder cylinder and pump capacity capac ity will will be D = 149.308 cm

Q = 28 LPM Power of electric mot motor or remain same. 2 • For 350 kg/cm working pressure, inside diameter of cylinder and pump capacity will be: D = 11.287 cm2 Q = 16000.98 cm3/min or 16 LPM Power of o f electric motor remains the same. • CETOP is an international standard for standardising standardising hydraulic hydraulic component. It specif spe cifies ies mounting dimension dimension and oil port. Fo r 16 LPM flow we select smallest smallest series s eries of CETOP standard st andard valves, that is CETOP-01 series valves. valves. • For 28 LPM we select CETOP-03 size of valves and for 80 LPM we select CETOP-6 size of valves. • As on today tod ay that is 26 th May 2008, cost of o f various various components are as follow: follow:

Sr. Sr. Componets Make No 1.

Motor

2.

Pump

Model Cost

Make

Model

PVR150-70

Rs Polyhydron 20070/-

2RCE-7DD

Rs 15400/-

Polyhydron 2R CE- 7- CC

Rs 15400/-

BG-06

Rs 3365/-

Polyhydron

DPRH-10-3200

Rs 1220/-

Polyhydron DPRS-06-S400

Rs 700/-

DMG-o6

Rs 5500/-

Polyhydron 4DL-10G10.S

Rs 1540/-

Polyhydron 4DC-1D-G103

Rs 1540/-

Rs 25000/-

Hydro Electric Machinery

Yuken

5.

ID-150 Hydro Hydro HydraulicCylinder ID-250 Rs Rod-80 Electric Electric (Dimension are Rod-100 70000/Machinery Stroke-500 Machinery Stroke-500 in mm)

8. Total Cost

Cost

Rs 21497/-

Direction Control Yuken Valve

Accessories

Model

15 HP Vertical

4.

7.

Make

Rs Hindustan 21497/- Motors

Relife Valve

Oil Tank

Cost

Hindustan 15 HP Motors Vertical

3.

6.

2 350 kg/C

2 200 kg/C

2 70 kg/C

Working pressure

Yuken

Hydroteck 800 ltr

Rs 13000/-

400 ltr

Rs 10000/Rs 143434/-

Total Cost

Rs 8000/Rs 8000/Rs 80655/-

Hindustan Motors

15 HP Vertical

Rs 21497/-

ID-120 Rs Rod-80 15000/Stroke-500 200 ltr

Rs 6000/Rs 6000/-

Total Cost

Rs 66155/-

From above example we found that system with high pressure are economical and low pressure are costly. With time the cost of component will change. But the difference of cost between smaller, medium and large size will always be there. Hence in every era the high pressure compact hydraulic system will be always economical than low pressure bulky system. • With increase of pressure, size of equipment and cost reduces, but maintenance problem increases. While at low pressure, size of equipment and cost increases. Hence pressure is decided carefully considering various factors. • In case of machine tools, the t he load on hydraulic cylinders cylinders are much less as compared to hydraulic hydraulic presse presses. s. If we select select high high workin working g pressur pressuree for them, them, and and try to calcul calculate ate the dime dimens nsion ion of hydrau hydrauli licc “Design and Manufacturing of Hydrauli Hydrauli c Presses.” Presses.” ©: Q.S. Khan Khan

10-5



cylinder, cylinder, then the n these dimensions may be less than 1 cm or only few few centimeters. cent imeters. Such S uch thin and small cylinder cylinder may not give sta stabil bility ity and maintenance free operation, opera tion, hence for machine tool, we generally select low working pressure, that is between 50 to 100 kg/cm2. work ing pressure But in general we have following • There is no hard and fast rule for selection of working range of working wo rking pressure for various systems in industry. industry. Sr. Sr. Filed of application No

Range of Working Pressure

1. Injecton Moulding Machine 2.

Pump

3.

Relife Valve

30 - 70 Kg/c 2

4.

Direction Control Valve

70 - 300 Kg/c

5. HydraulicCylinder

(Dimension are in mm)

2

210 - 350 Kg/c 210 - 350 Kg/c

2

2 2

40 - 250 Kg/c

2

6.

Oil Tank

140 - 250 Kg/c

7.

Accessories

350 - 700 Kg/c

2

Above data based on o n general study and old trend of o f industry. industry. Nowadays most of manufactures prefer, prefer, and design designss high high pressure pressure system system..


10-6



10.5 Pressure Drop in Hydraulic System The pressure pr essure drop dr op in hydraulic system is is basically due to t o resistance resistanc e to flow. flow. While While over coming co ming this resistance energy is lost. This loss of energy gets converted into heat, which increases temperature of working fluid. fluid. Pressure P ressure drop dro p is an undesirable undesirable phenomena, and following following are the main causes of pressure pressure drop in a hydraul hydraulic ic circui circuit. t. 1) Decrease in pump efficiency:-

Pump effici efficiency ency decreases due to wear and tear t ear of o f it’s it’s internal components, or due to rise in temperature. High temperature increases clearance between pump casing and moving element, element, through which high high pressure oil o il escapes back back to t o low pressure side. This cause pressure drop and further increase in fluid temperature. 2) Throttling in valves:valves:-

Valves are designed as per pe r CETOP standard, sta ndard, and oil hole in them are 6 mm, 11 mm, mm, 22 mm etc. These oil holes work like an orifice. orifice. Whenever large flow passes through thro ugh a small hole, the velocity of fluid fluid increases but pressure pressur e drops. dro ps. Similarly Similarly when fluid fluid passes through t hrough hydraulic valves, valves, there is some drop in pressure due to throttling. throttling. 3) Internal leakage leakage in valve:-

Direction control cont rol valve valve has a sliding sliding spool in valve valve body. Due to constant co nstant use u se sliding sliding contact conta ct area wears out. out . As As clearance increases internal leakage increases. When high pressure fluid leaks leaks through throug h these clearances, it causes drop dro p in pressure, and flui fluid d heating. What we have described for direction control co ntrol valves also hold good for all valves valves with sliding sliding spool and poppet po ppet and with metal to metal sealing sealing arrangement. arrange ment. (sealing by fine fine clearance) 4 )Valves )Valves with spring loaded poppet:popp et:-

Construction Const ruction of some valves are such that whenever fluid fluid passes through thro ugh them, then t hen it has to lift lift a spring loaded loaded spool spoo l or poppet or o r steel ball etc. Whenever fluid fluid pressure acts against such spring force to over-come compression of spring spring then some energy is is lost and pressure drops. Such valves are pressure pressu re reducing valves, valves, sequence valves, check valves, valves, pilot operated operat ed check valves, relief valves etc. 5) Resistance to flow flow through pipe line:-

Fluid experiences resistance to t o flow while passing through pipe line, joints and bends etc. Hence there ther e is pressure drop d rop at a t every joint and bend in pipe line. line. While passing through pipe line due to such resistance energy of fluid fluid is lost and pressure drops. drop s. • Pressure Pressure drop is studied studied carefull carefully y and and calcula calculated ted to ascertain ascertain the heat heat generation generation in in system, system, because because pressure drop reduces the system system effi efficien ciency cy,, and heat heat which which get generated generated damages damages the system. Hence special steps are taken ta ken at design stage to control co ntrol and keep both of them in safe limit. At every valve, valve, joint, and bend etc. pressure drop dr op could co uld be calculated with help of technical data available available in in design book. Once we get total tot al pressure drop, heat generated could be calculated.


10-7



10.6 Calculation of Heat Generation In Hydraulic System Heat generation due to loss of efficiency: The purpose purpo se of cal c alculation culation of heat generation in hydrauli hydraulicc system is to find find and use correct size and specification of oil cooling system.  A low capacity cooling system will will get overloaded, o verloaded, and may not not be able to maintain temperature within optimum temperature limits. limits. And a higher capacity capac ity cooling system will be costly, costly, and a nd cooli coo ling ng system itself will will utilise more more electric e lectric power, and may be under utilised. Hence to have right cooli co oling ng unit, correct corr ect estimation of heat generation generat ion is necessary. necessary.  Hydraulic Hydraulic systems are not 100% efficien efficient. t. As a thumb t humb rule we assume 80% 80 % efficiency efficiency,, and we assume that balance 20% input energy gets converted convert ed in to undesirable h heat. eat. So if we use 11.5 kw motor, moto r, then we assume that 2.25kw (That is 20% of 11.5KW) will get converted co nverted in to heat. So our cooli coo ling ng system should be able to extract 2.25KW of heat from hydraulic system. For extracting extract ing 2.25kw heat, w e rrequire equire 0.799 TR capac capacity ity cooling cooling system as per following following calculation. 2.25 (kw) X 860 = 1935 kcal/hr. 1935 = .06398 TR (Ton Refrigeration) 3024

If we assume 80% efficiency efficiency of cooling system, then 20% more mor e capacity is to be added adde d in cooling capacity 0.6398 = 0.7997 TR 0.8

Heat generation due to t o pressure drop: Second Seco nd method of finding finding amount of generated generat ed heat in system is is by calculating calculating amount of pressure pressure drop in system system.. The The energy energy lost in in form of pressure pressure drop get converted converted in to heat. heat.  Example: Considers Co nsiders a hydraulic system with following specificatio specification. n. 1) Motor Motor Hp Hp = 15 Hp or 11.5 kw 2) Capacity Capacity low flow flow and and high high pressure pump = 20 LPM 3) Capacity Capacity of hi high flow flow and and low pressure pressure pump pump = 70 LPM 4) System should have have foll followin owing g special special features. features. a) Pressure will will be be held in in cylinder cylinder by using using pilot pilot operated o perated check valve . System will will also also have flow control contro l to have variabl var iablee and contro co ntroll lled ed speed spe ed while pressing. System Syst em will will always have full full and maximum maximum approach and return speed. spee d. b) The detail detail of compone component nt used, used, and and hydraul hydraulic ic circui circuitt diagram diagram to fulfi fulfilll above above menti mentioned oned requirements are as per sketch No.___ Solution: To calculate calculate total t otal pressure drop, we have to calculate, pressure dro p in pipelin pipeline, e, pressure drop in hydraulic valve, valve, and pressure pres sure drop dro p in cylinder cylinder due to seal se al friction. friction.  Pressure Pressur e drop dro p in pipe pipe line could be calculated by using monog monogram/graph ram/graph  In present prese nt example we are using standard sta ndard pipe with 24mm inside inside diameter, and 33.4mm 33. 4mm outside 2 diameter. Pressure drop in pipe will be 0.1 kg/cm per meter for flow of 100 LPM (As per monogram). We assume that total t otal length of o f pipe line line will be 10 meter. met er. Hence approximately appr oximately total 2 pressure pressure drop in pipe line line will will be 1Kg/cm  Manufacture of hydraulic pumps and valves provides complete technical detail in their catalogue, including including pressure drop at various v arious pressure and flow. flow. So as per out working pressure and flow flow we can find find pressure pressu re drop from catalogue catalogu e of respective valve and pump “Design and Manufacturing of Hydrauli Hydrauli c Presses.” Presses.” ©: Q.S. Khan Khan

10-8



Pressure drop in hydraulic cylin cylinder der is due to seal s eal friction. friction. Loss o f energy to overco me seal friction is calculated aass follow. 

12

9 8

7

6

5 4 3

10

P

Sr.No. Components

1 2 3 4 5 6 7 8 9

Make Piston pump Polyhydron Vane-pump Yuken Unloading valve Polyhydron Check valve Polyhydron Relief vlave Polyhydron Direction control valve Yuken Pilot operated check valve Polyhydron Flow control valve Polyhydron Direction control valve Yuken

11

2

1

Make 2RCE7DD PVR-150-70 PPRU C-30-S-1 DPRS-10-S-315 DSHG-06-3C60-A240 CI-30-S 2PF-H-10-C-32 DSHG-06-2B2A-A240

10 Check-valve

Polyhydron C-30-S-4

11 Return line filter

Hydax

12 Hydraulic cylinder

Hydro ID Electric R od Machinery Stroke

RLF-10-25

=280 mm =170 mm =500 mm mm


Detail and Pressure Drop ------Pressure drop 2kg/cm 2 at 100 LPM Flow --Pressure drop 2kg/cm 2 at 100 LPM Flow Pressure drop 2kg/cm 2 at 100 LPM Flow Minimum pressure difference.5kg/cm difference.5kg/cm2 Pressure drop 6kg/cm 2 at 100 LPM Cracking pressure-5kg/cm2 Pressure drop 6kg/cm 2 at 100 LPM Cracking pressure-5kg/cm2 With clean oil not pressure drop.In clogged condition inbuild check valve open at 5kg/cm2. We assume 2kg/c2 pressure drop at normal working condition. Pressure drop 5kg/cm 2

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Total pressure drop at fast speed and low pressure will be. be. 2 2 kg/cm - cracking pressure o f check valve valve (1) 2 2 kg/cm - main direction direction control co ntrol valve (6) 2 2 kg/cm - pilot operated check valve (7) 5kg/cm2 - hydraulic cylinder cylinder (12) 2 2kg/cm - direction direction control valve valve to control co ntrol flow flow (9) 2 6kg/cm - check valve to develope back pressure to operated direction control valve valve (10) 2 2kg/cm - pressure pressur e drop in return line line filter filter (11) 

21 kg/cm2 Total pressure drop at low speed spe ed and high pressure will be be 2 2kg/cm - cracking pressure of check valve (4) 2kg/cm2 - cracking pressure of o f pilot pilot operated o perated check valve valve (7) 5kg/cm2 - pressure drop across a cross flow control valve (8) 2 5kg/cm - pressure drop due to t o seal friction friction in cylinder cylinder (12) 

14 kg/cm2 

After calculating calculating total pressure drop dro p heat generation ge neration is calculated calculated using followin following g equations. equat ions.

H=

10X60XPXQ 427

Where H = Heal in Kcal/hr P = Pressure drop kg/cm2 Q = Flow of pump in lpm 1 Kw/hr = 860 Kcal 1 Kcal = 827 Kgm 3024 Kcal/hr = 1 TR (Ton refrigerator) 10X60X21X90 =2655.7kcal/hr 427



In present example example heat generated generat ed is =



For removing 2656 kcal/ hr heat we need =



3024 = 0.878 TR Capacity cooler If we assume cooler coo ler effici efficiency ency as 80%, then t hen we should selected cooler co oler capacity as

0.878 X100 = 1.097TR 80 This calculation calculation is based based on heat generation gener ation at high speed and low pressure operation. ope ration. But system also operates for some time at low speed and high pressure in which which case heat generation is low. low. Hence actual act ual heat generation will be less than 1.097 TR. 1 TR is standard capacity of cooler, coo ler, hence hence we will will select 1 TR Air-cooled Air-cooled oil cooler (chiller) (chiller) in our system.  Another equation equa tion which could be used for for calculating capacity of water coo ler is is =

m x s x (t1-t2) X 60 = H (kcal/hr) Where m = mass of fluid fluid (LPM) S = specific heat of fluid.(it fluid.(it is 1 for water and 0.85 for mineral mineral oil) t1-t2= Temperature difference of fluid before and after cooling.


10-10



10.7 Sequence Sequence and Cycle Diagram Very few power packs are operated by hand. hand. Most of the power po wer packs are controlled and actuated actuat ed by electrical control panel. Press design, hydraulic hydraulic circuit design, design, hydraulic power pack manufacturin anufacturing, g, assembl assembly y and testing, testing, commi commissi ssionin oning, g, and maintenanc maintenance, e, all all these jobs are done by different different engineers. For better bet ter comm co mmunication unication and understanding among them there should be some some bluepri blueprint nt which which all all should should read, understan understand d and interpr interpret et without without any diff differe erence. nce. Hence for this purpose along with circuit circuit diagram, sequence chart and load cycle diagram diagram is also also made. Sequence Sequenc e chart contains, cont ains, sequence of energisation of various solenoid, and their controll contro lling ing parameter. Whil Whilee load cycl c yclee diagram indicates indicates stroke s troke,, load developed and tim t imee required. requ ired. An example of sequence chart and a nd load cycle diagram for a deep drawing press is as follow.

Pressure switch 15 PS1

4

13

12 Limit LS 3 switches

LS

LS

11

10

2

S2

8

S3

S

1

Blank-hilding cylinder 9 S5

4

S1

Unloading valve

6 7 4

16

15 14LPM 250BAR

M

V

P 70LPM 20BAR

15

15

15HP

Figure No. 35.25

16

17

Hydraulic Circuit Diagram of Deep Drawing Press

Operation of Deep drawing Press: 1. Pres Presss has four our blankank-h holdi oldin ng cyl cylinder der 13 and a main pressing cylinder 12. Four blank-holding cylinder cylinder operated operate d by a common solenoid-operated direction control valve4, while main cylinder cylinder operated oper ated by another direction control co ntrol valve8.


10-11


2. 3.

4. 5. 6. 7.


Two pum pumps are are use used d in whi which low pres pressu sure re pum pump2 is unload unloaded ed by unloading valve, which 5 is actuated, and control contro l by a solenoid solenoid valve valve . (S1) For deep deep draw drawiing operati operation on shee sheet-m t-metal etal blank blank is place placed d on presspress-tab table le manual anuallly. On pressi pressing ng push-bu push-button tton blan blank-h k-holdi olding ng cyl cylinder inder moves moves forward forward,, and presses presses the sheet-m sheet-metal etal blank. blank. Load Load is is sensed by pressure switch (PS1), which gives gives signal signal to main main cylinder cylinder to take its forward stroke. The depth depth of draw draw produc produced ed by by forwa forward rd stroke stroke of mai main n cyl cyliinder nder is is sens sensed ed by by (Lim (Limit switch) LS2, and this this stops forward stroke st roke and activate return stroke. Compl Completi etion on of return return stroke stroke is sensed sensed by limi limitt switch switch LS3 and it stops return return stroke stroke and and activate return ret urn stroke str oke of o f blank-holding blank-holding cylinder. cylinder. Return Return stroke stroke of blank blank-hol -holdi ding ng cyl cylin inder der is is sens sensed ed by limi limits ts swi switch tch LS1. LS1. It stops stops the the return return stroke of blank-holding cylinder. Eject Ejection ion is automa automati ticc and and achi achieved eved by mecha mechani nical cal mean means. s. Linka Linkages ges are are provi provided ded by by whi which ch the returning ret urning platen of blank-holder blank-holder also eject the drawn component. component . Drawn component removed manually and new blank-loaded manually. This makes press ready for next operation.

Sequence of Operation Chart SEQUENCE OF OPERATION

S1

S2

S3

S4

S5

CONTROLS/ ACTUATION ACTUATION BY

Start of Cycle Blank-holding Cylinder Cylinder Forward Stroke

OFF F Push-botton ON OFF OFF ON OF (Manual)

Main Cylinder Forward Stroke

ON ON

Main Cylinder Return Stroke

ON OFF ON

Blank-holding Cylinder Cylinder Return Stroke

ON OFF OFF OFF ON LS3

OFF OFF OF OFF F PS1 (Presure switch) switch)

OFF OF OFF F LS2

Completion of OFF F LS1 ReturnStroke and End of OFF OFF OFF OFF OF Production Product ion Cycle Cycle Note : S1, S2,S3, S4, S5 S5 are Solenoid Solenoid electrical electrical coil of valve valve No.5, 8, 9 Note: - A simpl simplee control contr ol panel uses contactor, co ntactor, push-button push-butto n etc.for etc. for actuation actuat ion of solenoid coil when control contr ol instrument such as limi limitt switch, pressure-sw pr essure-switch itch etc. get actuat ac tuated ed they give signal signal in in control panel. panel. And because because of which which as per the wirin wiring g and design design of panel panel, one one solenoi solenoid d get switche switched d off and other switch on.


10-12



Cycle Diagram: -

d e t a u t c A 1 S P

e k o r t S

d e t a u t c A 2 S L



n g n r a w i d w o S l o

0 0 7

r e d n i l y c n i a M

, g n i s n e . s p e r m u u s p s e r r e p u c s s i l e r u p a r d w o y l H f ) o l a g c i n i r d t c a e l o l E - n u n d o n N ( A

F a s t r e t u r n

h o c r p a p i d a p R

0

r e d n i l y c g n i d l o h k n a l B

0 0 5

Blank holding R e v e r s e

d r a w r o e F

k o r t S 0

Time Time

Cycle complete Cycle Figu gure re N No o. 3 35 5.26


10-13



10.8 Circuit Diagram For Modular Type Type Power Pack: Modular valves are ar e most widely used in indust industry ry because of o f convenience in using them. They do not require compl co mplicated icated manifold block block and piping. To represent the way and sequence in which which they have been stac stacked ked one above abo ve the other, ot her, while assemblylin assemblyling g a hydraulic system, their circuit diagram diagram is slightly modified. modified. We briefly explain it as follow fo llow..

Direction controll valve (4)

6

2

Relief valve for pump (3) Pilot operated check valve (6) Flow control valve (5) Return line filter

5

A B

Oil filler breather

4

Manifold block

Tank

1

3

2 1

M

P

Example of a Modular Valve stacked Figure No. 35.22

Figure No. 35.21

Above mention circuit is general hydraulic circuit circuit diagram. For modular valve same above circuit can also be drawn in following following ways.

A-port B-port

Pipe line

P

A

T

B

Direction control valve (4)

Direction control valve (4)

Tank line Flow control valve (5)

Relief valve (3)

Pilot opareted Check valve (6)

Check valve

Relief valve for Pump (3) P

P

T

T A

AB-r t po po r t

B Cylinder

Flow control valve (3)

Manifold or sub-plate

Pump (1)

Figure No. 35.23


Mani-

Pump line

Tank line

Tank Cover

10-14



Some of the logic and feature of making making such type of circuit is as follow follow.. 1)

2)

3)

4) 5) 6)

7)

As a commo common n pump pump line line and and tank tank line line drille drilled d throug through h mani manifol fold d for for numb number er of of sole soleno noid id valve valves. s. Hence a corresponding two straight horizontal lines are drawn as pump & tank line in circuit diagram. In case case of of modu modular lar valve valve,, all the the valve valvess have have same same hole holess namel namely y, P-(Pum P-(Pump), p), T-(Tank -(Tank), ), A&B A&B (both port of cylinder), As per international standard these holes of all the valves have same dimension, dimension, and perfectly per fectly match each ea ch other when staked one above the other. When valve stacked one above the other, four vertical pipe like passage forms. Oil passes through all the four line of all the valves, irrespective of whether valve requires those line or not. Hence we have drawn four vertical lines. As Pump Pump line line (P) and Tank line line (T) starts starts from from Pump Pump and and Tank Tank and mostly ostly passe passess throug through h direction control valve and ends at actuator (Cylinder or Motor). Hence out of four vertical lines two starts from Pump, Tank passes through direction control valve and ends at A and B-port of cylinder. Hence Hence two horizo horizontal ntal and four four vertic vertical al lin lines es are com common mon featu feature re in in this this type type of circ circui uitt diagram. As per per valve valve adde added d in circui circuit, t, thei theirr graphi graphicc diagram diagram drawn drawn bet betwe ween en corres correspo pond ndin ing g six six lines lines.. For For bette betterr under understan standi ding ng a dotte dotted d line line is draw drawn n for for mani manifo fold ld and valve valve.. Each Each dotte dotted d bloc block k indicates one unit of valve or manifold (sub-plate). We have have drawn drawn abov abovee circui circuitt diag diagram ram for for one one valve valve bank bank (set (set of of a valv valve) e).. More More num number of valves bank could be added on manifold, using same pump and tank. If a relief valve, pilot operated check valve, flow control valve and direction control valve is further added to operate one more cylinder in same power pack with common pump and motor, then new circuit diagram will be as follow.

Second Valve Bank

Direction controll valve

First Valve Bank

P

A

P

A

T

B

T

B

Direction controll valve

Flow controll valve

Flow controll valve

Pilot opareted check valve

Pilot opareted check valve

Relief valve for pump

Relief valve for pump P

P T B

B A

Tank

Manifold or

T

New Cylinder

A Cylinder

Pump

Figure No. 35.24


10-15



10.9 Use of filter in Hydraulic Circuit:Circuit:A hydraulic circuit could cou ld be designed in five ways to filter oil in system. 1) Circuit with suction stainer:In this design a filter filter is provided pro vided at suction su ction side of pump. Advantage of this design is that it prevents preve nts entry of o f large size contamination contamination in system. Which may may cause immediate immediate and severe se vere damage to system. Disadvantage of this design is that fine filter could not be used at suction side as this t his may result in high pressure drop dro p in suction, which will cause cavitation in pump. Generally 150 mesh size filter which can filter filter upto 100 10 0 micron size particle are used in suction stainer sta iner.. 2) Circuit with disch discharge arge line or return return line filter:In this design the oil exhausted to tank are filtered. filtered. Advantage of this design is that it can tolerate high pressure drop dro p as compared to suct suction ion stainer, so the t he filter filter with filtering capacity of 10 micron could be used. Disadvantage of this design is that some valves such such as proport pro portional ional or servo valve require less than 5 micron cleanliness. If we use 5 micron micron filter filter at return line then it wil w illl cause excessive and constant const ant back-p back-press ressure ure which which is undesi undesirab rablle. He Hence nce fine fine filteri iltering ng elem element ent could could not be used in return line line filter. filter. Suction stainer sta iner and return line line filter filter do have some disadvantages, but because of protection they provide to the system, system, they are almost almost compulsory part of all hydraulic circuit. 3) Circuit with pressure line filter:For absolute abso lute cleanliness cleanliness of oil pressure line line filter filter is used. But use of o f this filter filter causes excessive pressure pre ssure drop dro p in system. system. 4) Pressure line bleed-off filters:Suction stainer st ainer,, return retu rn line line filter filter or o r pressure pressur e line fil filter ter are selected as per pump capacity capacity of system. system. For very high high capacity pump, vary large capacity of fil filter ter is required, which w hich may be vary costly. costly. For simple simple economical econo mical system, and those t hose system, where involvement of contami conta mination nation is very less, pressure line line bleed of type circuit is used. In this system through throu gh an orifi o rifice ce a small quantity of oil is discharged to tank through t hrough filter. filter. Advantage of o f this system is that a small size size filter be used in the filte filteri ring ng system system.. Disadv Disadvan antage tage of this this system system is that the oil passing through thro ugh orifi or ifice ce for filtering is lost lost from the effective pump output. 5) Independent filtration circuit:This type of o f circuit is also called kidney loop or o r off line line filtering system. In this system a separa separate te pump is used to filter filter oil o il.. Generally for for large and critical hydraulic system this is used. The fluid fluid which is circulated by independen independentt pump pump for fil filtration may also also pass pass through cooler to maintaining maintaining temperature temperatu re of o f fluid. M


M

M

M

M

M

10-16



10.10 What is Pumping Unit and Powerpack Unit? In case of huge machinery like like steel rolling rolling plant etc where more number o off hydrauli hydraulicc actuato ac tuator r and control of hydraul hydraulic ic actuator are used, system could be designed designed and made in in two ways. In first first method the control co ntrol and manifold manifold block block of each actuator could co uld be placed very near to actuator actuato r (which may be a cylinder and motor) mot or).. And And pump and moto mo torr which are common co mmon to all manifold manifold are place placed d at long long dista distance nce at some some suitab suitable le place place.. As in this this case case motor, motor, pump, pump, relie relieff valve valve and and reserv reservoi oir r assembly supply only oil to all the manifold manifold block. And do no control contr ol each actuat act uator. or. Hence they are ar e called as pumping unit In pumping unit unit we have few advantages such as: Length of pipe between manifold manifold block and actuator act uator are less and hence less cost co st of piping, less possibi possibili lity ty of leakage, leakage, less problem problem of spongines sponginesss and compressi compressibi bili lity ty of oil ete. While While in power pack design, d esign, manifold manifold block and valves of all actuators actuato rs are mounted on o n single oil reservoir. And And from manifold manifold block long piping piping are laid laid to all the actuators. actuat ors. Power Powe r pack type of design also have some advantages over pumping pu mping unit, unit, such as maintenance maintenance of hydraulic hydraulic equipment is is easy. easy. Because of o f more number of long piping piping heat of o f oil oil get dissipated. We get more space around ar ound actuato act uator, r, as control contro l unit unit (manifold) (manifold) is on reservoir etc. Control units

Actuators

Motor and Pump assembly

Oil Tank

Pumping Unit

Control units

Actuators Motor and Pump assembly

Oil Tank

Power pack unit “Design and Manufacturing of Hydrauli Hydrauli c Presses.” Presses.” ©: Q.S. Khan Khan

10-17


Pressure Control Circuit

10.11 Pressure Control Circuit 1.

There should should be alw alway ayss a relie relieff val valve ve to control the maxi maximum mum pressure pressure of the system system.. Relief valve should be immediately immediately after pump, so that t hat due to any a ny reason if oil flow flow generated generated by pump gets blocked blocked then it can pass through relief relief valve, valve, without without damagin damaging g any other parts of the system system.. Pressure relief valve

P

M

Figure No 10.11.1

2.

When When two pumps pumps are used used in in a system system in which which one one pump pump is is with with high high flow flow and and low low working pressure for fast approach appro ach and return speed, and second pump p ump is with with low flow capacity and high high working pressure pres sure for actual pressing press ing operation. operat ion. Then after reaching certain pressure high flow flow pump is required to be unloaded to tank to avoid excessive excessive load on prime-mover. For such application “Unloading type relief valve” is used as shown in following circuit diagram. Oil at low pressure to hydroulic system

Figure No 10.11.2

Main relief Valve Valve of system

M

P

P

Pilot opereted unloading relief Valve

High Pressure Pump Low Pressure Pump

High pressure oil to system for pressing operation.

High pressure piolt piolt Line

High flow and low pressure pump discharge unloded to tank through unloading relief Valve

Pilot opereted unloading relief r elief Valve Valve

P

M

P

Figure No 10.11.3

Hydroulic circuit diagram when unloading valve got actuated act uated


11-18


Pressure Control Circuit

In a hydraulic hydraulic circuit when different different pressures are required at different different stage of o f operation, then t hen following following type of o f arrangement of direction control co ntrol valve and pressure relief valve could be used. If pressure pressur e setting set ting of ‘Pressure ‘Press ure Relief Valve-A Valve-A’’ and ‘Pressure Relief R elief Valve -B’ are lower than system pressure, pressur e, then when solencid-1 so lencid-1 is energized, energized , then maxium pressure in system will will be as per Pressure Press ure Relief Value Value -A and when solenoid-2 solenoid- 2 is energized then the n maximum maximum pressure pressu re in system will be as per Pressure Pressure Relief Relief Valve-B alve-B.. And when when both the solenoi solenoids ds are switched switched off then maxi maximum mum pressure pressure wil will be as per setting setting of relief relief valve-C valve-C.. Unloadi Unloading ng reli relief valve valve D in circui circuitt 35.2 will will only only control pressure of low pressure pump. (Fig 35.2)

Pressure requires as per setting of pressure relief valve


B

C


A

Sol. 2

B

A

Sol. 1 C

D

High pressure pilot Line

P

M

P

Figure No. 10.11.4 Hydroulic Hydroulic circuit diagram when unloading valve got actuated.


10-19

Pressure Holding Circuit


10.12 Pressure Holding Circuit (By using pilot pilot operate o perated d check valve)

Many time time hydraulic hydraulic presses are required requ ired to hold ho ld the job under compression for very long period period of time. time. For For such operation if motor oto r runs continuously continuously to develop develop pressure pressure for pressing pressing operation operat ion then it will be be uneconomical uneco nomical,, due d ue to excessive electric consumption. Also oil will will get heated up, u p, as most of the pump pu mp discharge will will pass through thro ugh the relief valve. valve. For such application application pilot pilot operated check valve is used in circuit. circuit. Which hold the pressurized oil in cylinder cylinder or o r system syste m for for long lo ng time. A simple circuit of this t his type is as follow. fo llow.

There should not be any pressure in pilot line of pilot operated check valve. Otherwise pressure not be held in system.

Pressure held in cylinder cylinder in neutral position

Pilot operated Check valve

P

M

Figure No 10.12.1 Pressure held in cylinder at neutral ne utral position.


10-20


Pressure Holding Circuit

For return retu rn stroke-pilot stroke-pilot pressure is given to unlock the pi pilot lot operated oper ated check valve and release pressure in cylinder

P

M

Pressure Pressur e released from cyli cylinder nder for return retur n stroke. Figure No 10.12.2


10-21

Decompression Circuit


10.13

Decompression Decompression Circuit

This is a feature of hydraulic circuit. When high pressure pres sure fluid is held in cylinder, cylinder, and when this high high pressure is suddenly sudde nly released, then a surge su rge of o f large large volume of fluid fluid passes thro ugh the pipel pipelin inee and produces produces a banged banged sound and vibrati vibration. on. Sudden Sudden release release of stresses stresses also also cause cause Jerk Jerk in in press-bod press-body y. To avoi avoid d this, this, pressure pressure is slowl slowly y reduced reduced to mini minimum mum possibl possible, e, then cylin cylinder der allowed allowed to retract. ret ract. This T his feature of o f slow slow release re lease of high high pressure pressur e in system is called called decompression.

a. b. c. d. a)

For Decompression four types of circuits are used. Decom De compr pres essi sion on circ circui uitt usi using ng an orif orifice and and ch check eck val valve ve.. Decompr Decompress ession ion circui circuitt usi using ng orifi orifice and solenoi solenoid d operated operated directi direction on control control valve. valve. Decompr Decompress ession ion circui circuitt usin using g valve valve which which have have in-b in-bui uild ld feature of decompress decompressiion. Decom De compre press ssiion by by dire directi ction on control control valve valve (slow (slow move moveme ment nt of its spool spool). ). Decomp Decompre ressi ssion on circuit circuit using using an an ori orific ficee and and che check ck valve. valve.

In following circuit circuit diagram diagra m when pump develops pressure, press ure, no oil will will flow through throug h check valve. Only in neutral position of solenoid operated direction control valve, pressurized oil of cylinder cylinder will slowly slowly press over check valve to tank. t ank. Due to t o orifice the release o off pressurized oil o il will will be very very slow. slow. This This arrange arrangem ment cannot cannot be used when there there is alway alwayss a pressure pressure in pump pump line. line. (Fig. (Fig. No. 35.4)

Check valve and orifice orifice for decomdec om pressi pression on

P

M

Figure No 13.1


10-22



b) Decompression circuit using orifice and solenoid operated direction control valve.

When there is always always a pressure pressur e in system, system, then above abo ve mentioned arrangement cannot be used. In such case cas e a direction control cont rol valve in place of check valve is better bett er alternative. alternat ive. In following following circuit when two-way-two two -way-two-position -position solenoid so lenoid valve valve is energies, it releases oil o il to tank. t ank. Due to orifice orifice there will will be be gradual drop in pressure. (Figure No. 13.2)

Valve for Decompression Feature

P

M

Figure No 13.2

(Pressure held in first first cylinder cylinder is getting gett ing De-compressed) Status of Pressure in Neutral Position Position after forward stroke


10-23



c. Decompr Decompress ession ion with with in-buil in-build d featur featuree in valves: valves: Pilot operated oper ated check che ck vale, pre-fill valves etc. can also have decompression deco mpression feature in their basi basic desi design. When When such such valve valvess are used, used, they automa automati tical cally ly reduce reduce pressur pressuree gradual graduallly. Detai Details of such valve have been described in chapter chapter No. 31. d. Decompr Decompressi ession on by directio direction n control control valve: valve:

Spool Spoo l of direction direction control cont rol valve valve changes its position from one finite finite condition to another a nother in fract fraction ion of a second. In tra transit nsit condition the pressuri pressurized zed port may get connected connected to tank as explained in following figure. This causes a sudden drop dro p in pressure resulting in large sound and vibration.

Finit Position

Transite position in which all port are connected to tank. Figure Figure No 13.3

To avoid this situation, situation, a pilot pilot operated check valve valve could be used to hold ho ld pressure in system when solenoid operated valve is changing position, and then decompress the pressure by three methods method s discussed earlier. Second method to reduce the sudden fall of pressure is is to move spool so slowly that pressure pressure drops slowl slowly y. Some type type of solenoi solenoid d valves valves have have in-bui n-built lt features features to move move spool slowl slowly y. In case of pilot operat operated ed solenoid valve without without in-built in-built decompression feature, a thrott t hrottle le cum check valve is is used between pilot valve and main direction control cont rol valves valves for decompression deco mpression purpose. Throttle cum check valve valve controls the flow flow of oil in pilot pilot lin linee to main main direction direction control valve, which shift shift the spool. spo ol. Reduced Reduc ed oil flow flow in pilot line line slows down the t he movement of spool spoo l results in slow fall of pressure in system.

Throttle cum check valve reduces r educes the flow of oil in pilot line to main direction valve, resulting is slow shifting of spool Pilot line to main Direction control valve Pilot valve Main Direction control valve Orifice

P

M

Back pressure get developed develope d in system due to orifice.

Figure No 13.4


10-24

Hyd. Circuit with back pressure


10.14 Hydraulic Circuit with with Back Pressure: A backpressure may be required in a hydraulic hydraulic system to operate o perate a pil p ilot ot operated operate d directional control valve. For such suc h back pressure an a n orifice orifice or a check valve valve is used, as shown in following following circuit diagram. Orifice Orifice and check valve is is used just after a fter high-pressure high-pressur e pump while a check valve could be used in return line line of system system also. also. But But when when orifi orifice ce and check check valve valve is used, we cannot cannot change change or vary the back pressure. For Fo r accurately accurat ely select and vary the backpressure special backpressure backpressure valve is used in return line, in place place of o f simple simple check valve (Fig. (Fig. No. No . 35.9) 35. 9) By using backpressure valve we can exactly vary and select the backpr essure. While by using a check valve back pressure will be fixed fixed and as per p er the cracking pressure pres sure of spring of check valve.

Main directio direction n controll cont roll Valve Valve

Pilot Valve Valve Opereted Operet ed by Back Pressure

A P

B Y

Orifice Orifice to develop Back Pressure

P

M

Figure No. 14.1 14. 1

Back pressure pre ssure in system by using orifice. orifice. In place orifi o rifice ce a check valve also could be used.


10-25



An orifice orifice should shou ld always always be used after afte r a relief valve, so that if any dust particle p article get struck s trucked ed in orifice, orifice, then t hen build-up build-up pressure will not damage d amage the pump p ump and system.

Main directio dir ection n controll contr oll Valve Valve

Pilot Valve

Back Pressur P ressuree Valve Valve

P

M

Figure No. 14.2 Back pressure pr essure in system by using back pressure pressur e relief valve valve in return line


10-26



10.15 Back pressure pressure in a hydraulic cylinder (Counter (Counter balance circuit)

Suppose a heavy load is hanging hanging from the piston rod. In such case in forward stro ke the cylinder cylinder may travel at higher speed than t han speed possible pos sible by by pump capacity (discharge volume) of o f system. In such case vacuum gets get s created in cylinder, cylinder, and oil starts star ts evaporating, evapo rating, resulting resu lting in spongy action of cylinder. cylinder. To avoid over running of piston rod under load, a back pressure is developed in the return port of cylinder using counter balance valve as shown in following circuit diagram.

Back pressure pressu re in system system as per setting of o f Counter Balance Valve, Valve, which holds the load in position.

Check Valve Valve for free reverse rev erse flow

Counter Balance Valve

P

M

Figure No. 10.15.1 Status Stat us of pressure in in natural position after after forward stro ke.


10-27



Check-Valve Check-Valve for free reverse rever se flow

Counter Balance Valve Passing oil after after generating g enerating desired pressure

P

M

Forward stroke Figure Figure No. 10.15.2


10-28



Check-Valve Check-Valve for free reverse reve rse flow Load

Counter Balance Valve

P

M

Figure No. 10.15.3 Reverse stroke “Design and Manufacturing of Hydrauli Hydrauli c Presses.” Presses.” ©: Q.S. Khan Khan

10-29



10.16 Hydraulic Circuit Using Sequence Valve Consider a hydraulic hydra ulic press, which has a job-holding or fixing fixing clamp, operated oper ated by hydraulic hydraulic cylinder. cylinder. When When press is operated, oper ated, first clamp clamp cylinder cylinder is required to get actuat a ctuated ed and clamp the component. component . And And after clamping clamping component compo nent at certain c ertain pressure, main cyli cylinder nder is required to be actuated actuate d for pressing operation on o n the component. co mponent. By using a sequence valve valve said requirement could be economi econo mically cally achieved. achieved.

Main Pressing Cylinder Clamp Cylinder

Sequence Valve

P

M

Figure No. 10.16.1 Forward Forwa rd Stroke actuated actu ated only for clampin clamping g cylinder cylinder In above circuit as soon so on as solenoid s olenoid valve valve actuated. act uated. First clamp cylinder cylinder will will clamp clamp the component, and after developing certain pressure and as per pressure setting sett ing of sequence valve, valve, sequence valve will allow main cyli cylinder nder to t o be actuated act uated.. Hence a performance which was possibl po ssiblee by using using a costly costly directi direction on control valve valve can be achieved achieved by using using a economica economicall sequence sequence valve. valve.


10-30



Main Pressing Cylinder

Clamp Cylinder

Sequence Valve

P

M

Figure No. 10.16.2 Forward Forwar d Stroke Strok e actuated only for main cylinder cylinder


10-31




Clamp Cylinder

Sequence Valve Make circuit for clamping them pressure total two

P

M

Figure No. 10.16.3 Status Stat us of presure in in neutral position after forward stroke stro ke


10-32



Clamp Cylinder


Sequence Valve

P

M

Figure No. 10.16.4 Return Stroke “Design and Manufacturing of Hydrauli Hydrauli c Presses.” Presses.” ©: Q.S. Khan Khan

10-33


Direction Control Circuit

10.17 Direction Directi on Control circuit Hydraulic Circuit For Actuating Number of cylinder with common Motor and Pump:-

When more than one cylinder is used in a system, system, and an d all the cylinders are required requ ired to be actuated actua ted independently independe ntly,, then more than one o ne direction control contr ol valve in in circuit is is required. If the basic basic requirement of circuit is that when cylinders are not actuat a ctuated ed (in idle idle condition), pump p ump should be unloaded to tank. And And when cylinders cylinders are actuated actu ated then t hen only pressure gets developed. developed . This could be achieved achieved in number number of ways ways as follow. ollow. a. Usin Using g Ten Tendu dum m typ typee dir direc ecti tion on cont contrrol valv valvee in in ser serie ies: s: -

P

M

Figure Figure No. 10.17.1 Status Stat us of pressure in neutral position after after forward stroke. str oke.

 



This circuit could co uld operate oper ate each cyl c ylinder inder independently, independently, but not simultaneously simultaneously.. nd rd Working pressure pre ssure of o f 2 and 3 cylinder cylinder will depend on the pressu p ressure re rating of first solenoid so lenoid valve valve at its tank port. po rt. (It is generally generally 100 Kg/Cm²) As all the time oil passes from all the direction direc tion control co ntrol valve hence there t here will be a pressure pres sure drop and oil heating, if pump of high discharge discharge is used. used .

b) Hydraulic Hydraulic circuit to operate operate more number of cylinders cylinders using all-port-block all-port-block valve valve and solenoid operated unloading valve.  In this circuit all the cylinders cylinders can ca n have high pressure.  When none-of the cylinder is actuated, unloading valve will unload pump discharge to tank. When any solenoid operated oper ated direction directio n control contro l valve valve gets activated, activated , solenoid valve of unloading valve valve should also be actuated actuate d to develop pressure in system. system.  When lever lever operated opera ted direction control co ntrol valves are used then addition direction control contro l valve valve is used in place of unloading unloading valve to unload the t he pump when not in used, and to develop d evelop pressure when required. Pressure Pres sure developing direction control cont rol valve is is always operated oper ated with all the direction direction control valves. valves.


10-34


Direction Control Circuit

1

3

2

When solenoid valve no. (1) get de-energised oil passes to tank via via pil pilot operate operated d relief valve.

4

M

P

Figure No. 10.17.2 Status of pressure in Neutral Position after forward stroke.

Oil passing passing to tank tan k at atmospheric pressure through throug h this valve in neutral position

2

1

P

3

4

M

Figure No. 10.17.3 Status of pressure in Neutral Position after forward stroke.


10-35


Regenerative Circuit

10.18 Regenerative Circuit This is special special type of circuit, and named as regenerative circuit, because we re-us e the exhaust oil o il coming out from fro m return port po rt of cylinder while cylinder cylinder is taking forward forwa rd stroke. stro ke. And exhaust oil o il along with pump discharge is supplied again to the t he cylinder cylinder for its forward st roke. roke . Following circuit will explain its princi pr inciple. ple.

A

B

2 1

1

2

P

M

Oil from return port of cylinder gets mixed with main discharge of pump through the check valve No.2. No.2. (As oil passes through check valve No.2. There is some pressure in system system as per cracking cracking pressure of check valve No.2)

Figure No. 10.18.1 Forward Stroke Stro ke at low low pressure


10-36



Oil From B-Port passi passing to tank tank through through relief valve valve No.2 No. 2 .

A

B

2 1

1

2

P

M

Figure No .10.18-B Forward stroke under pressure Oil will will not pass pa ss through throu gh check valve (2), because becaus e there is higher higher pressure pr essure on o n pump side. side.


10-37



A

B

2 1

1

2

P

Oil will not pass through check valve valve no.2, as pressure on both side side are same. same.

M

Figure Figure No. 10.18-C Return stroke


10-38



A

Pressure is locked locked in forward pipe line, Because direction control valve keeps the t he oil locked in cylinder port in neutural position

B

P

M

Figure No. 10.18-D Status of Pressure in Neutral Position after forward stroke. 







In re-generative circuit as all the oil exhausted from B-port combined combined with pump disch d ischarge, arge, and supplied to port-A. Hence cylinder speed will be more than the speed which could be achieved by using only pump. If the cross-section cros s-section area of ram is exactly half half of the cross-section cro ss-section area of cylinder. cylinder. Then we get same forward and reverse speed. As pump pressure increases, increases, back pressure at B-port also increase. Due to higher higher backpressure the effective compressive load which cylinder cylinder can develop de velop get reduced correspondingly corresp ondingly.. To reduce backpressure many arrangements arrangements are used. u sed. Some S ome of which are as follow. follow.


10-39


a)


When after after dev devel elopi oping ng pres pressur suree cyl cylinder inder does does not not have have to travel travel any any long longer er,, as in in case case of coining, embossing etc. then an orifice orifice provided pro vided parallel to check valve reduces reduc es the build-up build-up backpress backpressure. ure. But this this also also reduces reduces forward forward speed speed slig slightl htly y. Because Because from from return port some oil escapes from orifice orifice and returns ret urns to tank t ank (instead of o f getting mixed mixed with pump discharge).

Pressurised oil in this side escapes to tank via throatle if movement of main slow downs. (In fast forward motion as all th e oil can not pass through throattle hence either they get mixed with main pump flow or get reliefed by relief valve No.2)

P

M

Forward stroke under pr essure by very slow slow movement movement (for for coinin g forming) Figure No 10.18-E


10-40



As very small quality of oil can pass through throatle, hence maximum oil of return port gets mixed with pump discharge and supplied to forward stroke.

A

B

throatel

2

1

2

P

M

Figure Figure No. 10.18-F Forward stroke under pressure pres sure and fast movement (before coini co ining ng and forming forming operation) o peration)


10-41



Regenrating circuit with unloading valve in return port of cylinder A

B

2

1

2

1

P

M

Figure No. 10.18-G

Forward stroke without pressure (A-Port side of o f piston piston area is larger larger than B-port side of piston area Hence a slight pressure on A side develops high pressure on o n B side. Oil on high pressure gets get s mixed mixed with oil on lower lower presp ressure through check valve No.2)


10-42



b) In followi following ng circui circuitt as as soon as some some pressure pressure gets developed developed at A-port, oil comin coming g out from from B-port gets unloaded to tank through thro ugh unloading relief relief valve. Hence backpressure gets get s minimini-

A Unloading relief valve, valve, releases oil oil of B-port to tank at low pressure

B

2

1

2

1

P

M

figure figure No. 10.18-H 10. 18-H Forward stroke under pressure (After (After facing facing resistance when pressure o f A-port side increased more than B-port side, oil stops mixing mixing through thro ugh Check Valve Valve No.2) No. 2)

mized. “Design and Manufacturing of Hydrauli Hydrauli c Presses.” Presses.” ©: Q.S. Khan Khan

10-43



A

2

B

Relief Valve Valve for B-p

1

2

1

Pressurised Pressurised oil o il of B-port under pressure p ressure gets get s released to t o tank via Check Valve Valve No.2

P

M

Figure No. 10.18- I Status of Pressure in Neutral Position after forward stroke


10-44



A

B

P

M

Figure Figure No. 10.18-J Return stroke


10-45

Brake Circuit


10.19 Brake Circuit When moto motorr rotates rotate s at a load. Even after the supply to motor moto r switched off, due to inertia of load motor moto r keeps on rot ating. To stop the moto r following following circuit may be used.

P

M

Figure No. 10.19.1 Forward stroke.


10-46

Brake Circuit


P

M

Figure No. 10.19.2 Reverse stroke.


10-47

Brake Circuit


Back pressure in returen line of motor.

Back pressure valve

M

P

Figure No. 10.19.3 Neutral Neutral Positi Position on Due to back-presure valve, valve, motor faces a constant resisting pressure or force. This offers offers resistence resistence to extra rotation ro tation of moto motorr due to inertia of rotating load. “Design and Manufacturing of Hydrauli Hydrauli c Presses.” Presses.” ©: Q.S. Khan Khan

10-48


Flow Control Circuits

10.20 Flow control circuits Meter-in type circuit:In meter-in type of circuit we control co ntrol flow of oil entering entering on actuator. Q = Pump Pump output (LPM) Q1 = Fluid volume (supplied to actuato act uator) r) Q2 = Fluid Fluid volume returning to tank (through (thro ugh relief valve) P = Pump Pump pressure (kg/c2) P1 = Back-pressure in actuator due to resistance 1 A = Area of cylinder cylinder (cm (c m2) Loss of o f energy in Meter Meter-in-type -in-type will be be

A1 P1 F

Q1

P Q2 Q

M

Le =

PxQ2 _ (P-P1)xQ1 (Kw) 612 612

Figure No 10.20.1

P A1

A2

P2

Meter out type circuit:In meter-out type of circuit circuit we control co ntrol flow flow of o f oil exhasting exhasting (comig -out) from actuator. Q2 = Q-Q1

Q 1

P2 =

For same working presure presur e and same setting of fflow low control contr ol valves, the energy loss is same in metermeter-in in and meter-out circuit.

P Q2

M

(PxA)-F A2

Q

Le =

PxQ2 _ (P-P2)xQ1 (Kw) 612 612

Figure No 10.20.2 A1 F

Bleed-off type circuit:In bleed-off circuit circuit by by-pass extra oil to tank.

Q2 Q1

P=

F A1

Loss of energy = Le =

PxQ2 (Kw) 612

In bleed-off type circuit the loss of o f energy is less less than meter-in or meter-out type t ype of circuit. circuit. P

M

Q

Many time time different different speed of actuator actuat or required re quired using single pump. In such situation foll fo llowing owing circuits are used dependin dep ending g on o n requirement

Figure No 10.20.3


10-49


A1


TWO SPEED CIRCUIT F

4) Two Two speed circuit:circuit: In this circuit we have option of having full speed, which we achieve by by-passing by-passing flow control contro l valve. valve. Or we can have controlled speed by using using flow flow control control valve. valve. Directi Direction on control Direction c o n t r o l valve No.2 we use for fo r by-passing or blocking valve 2 the flow

1

P

M

Q

Figure No 10.20.4

TWO CONTROL SPEED

FV1

FV2

DIRECTION CONTROL VALVE 2

P

M

Q

Figure No 10.20.5


5) Two Two control speed:speed :In previous circuit we had one full speed and second controll contro lled ed speed. But if we want to have two controlled speed then followng followng circuit is used. In neutral position po sition of direction control valve No.2. We We have speed as per setting setting of flow flow control contr ol valve number number - FV1 .And when direction control cont rol valve valve No.2 is energised energised then we have speed as per combined combined setting of o f FV1 & FV2.

10-50



Functioning of two speed circuit

A

(In this circuit circuit both bot h the speed could c ould be adjusted).

DCV in high speed energies condition hence oil flow FV2 through flow control Valve isolatede because of colenoid valve in de-energised conditions.

Flow Control Valve

B FV1

M

P

M

P

Figure No 10.20.2

Forward stroke. Figure No 10.20.1

Figure No. Forward stroke (First slow speed)

D

C

P

M

P

M

Figure No 10.20.4 Figure No 10.20.3

Status of Pressure in Neutral Position after forward stroke


Return stroke.

In this circuit we have used meter-in type flow-c flow-contro ontroll valves. valves. To To have two speed spe ed of actuator we have used one more flow control cont rol valve along with a solenoid valve in parallel parallel with first first flow flow control valve. valve. Same arrangement can be used for meter-out meter-o ut as well as Bleed-off circuit. 10-51



6) Three speed circuit:In this circuit first speed is full speed without w ithout any control; contr ol; second speed sp eed is as per flow control contr ol valve FV1. and third t hird speed is as per combined setting of FV1 & FV2. This manupulation we are able to do by using special valve. valve. (Model (Mod el No, UCF2-04) made by M/s. Yuken Yuken India Ltd.

•

In first position we by-pass FV1 & FV2. Hence get rapid ra pid speed (full speed)

•

In position 2 we by-pass FV2. Hence get medium speed as per setting of FV1 .

•

In 3 rd rd posi positi tion on,, we we get get spe speed ed as per per combi ombine ned d set setti tin ng of of FV1 & FV2.

FV1 1

2

3

FV2

Q M

•

Three Three speed also also could could be achieved achieved by by using using fol followi lowing ng circui circuitt diagram diagram.. A1 F

S3

• S4

• •

FV 1

When S3 & S4 are are in in sw switch tch of off condition condition , we get speed as per FV1. When When S3 ener energi gise sed, d, we we get get spee speed d as as per per FV2. When When S4 en energi ergise sed d , we get get spee speed d as per per FV3.

FV 2

FV 3

M

Q


10-52



SLOW ST S TART AND STOP STO P, AND FAST MOVEMENT MOVEM ENT CIRCUIT CIRCUI T To have slow start and stop and fast movement of actuator, we use folllowing circuit diagram. F

FV 3

FV 2

FV1

S1

S2

FV 4

S3

S4

M

S1 S3 S3 S1 S2 S4 S4 S2

ON ON O FF O FF ON ON OFF OF F O FF

-

Slow start (Flows as per FV1.) Full speed (Flows as per FV1.+ FV3.) Slow stop (Flows as per FV1.) Stop Slow retraction (Flows as per FV2.) Fast retraction (Flows as per FV2.+ FV4.) Slow completion of retraction tion (Flows ows as per FV2.) Completion of retraction (Stop)


10-53



8) Continuous speed speed control (Autometic speed speed control):control):To have continuous continuous speed control co ntrol as per the demand of process, we have to use proportional pro portional electro-hydraulic flow control valve as per following circuit.


10-54


Synchronisation Circuit

10.21 SYNCHRONISATION SYNCHRONISATION CIRCUIT By using four flow control valve we can synchronize speed of two-cylinder. But this is not a foolproof system. system. Error Err or may occur and may accumulate accumulate with every stroke. Hence error after every stroke must be corrected. corrected . One of the method of co rrecting rrecting error is to provide pro vide lim limit it switches for both forward and return stroke of both the t he cylinder cylinder (Total four limit limit switches). And when both the t he limit limit switches at one o ne end are actuated actua ted then only cylinder cylinder will will take the t he next stroke. strok e. Hence on each stroke st roke the t he error difference in stroke gets corrected. co rrected. Synchronization Synchronization could be achieved more accurately by using pressure and temperature compensated co mpensated flow flow control cont rol valve. 1. Synchronisation by using pressure and temperature temperature compensated flow control valve valve

Figure No 10.21.1

By using using pressure and a nd temperature temperat ure compensated co mpensated flow flow control co ntrol valve we can achieve synchronisation in stroke distance dista nce up to 95%, 95 %, but stil st illl 5% variation may may exist. To avoid cumulation cumulation of error in stroke, stroke , at the end of each stroke error should be corrected.


10-55



2. Synchronisation by using more number of pumps -

If each cylinder is provided with individual pump with perfectly same flow, and individual direction control cont rol valve, then synchronisation in stroke str oke could cou ld be more more accurat a ccurately ely achieved. But if load on o n individual individual cylinder cylinder are ar e different different,, the pump discharge will again vary, vary, resulting re sulting in variation in stroke. In I n this case also the error should be corrected at end of stroke. Providin Pro viding g individual individual pump for individual individual cylinder cylinder is very costly co stly option. Hence Tedium gear pumps pumps type type flow flow divi dividers ders are used used for synch synchroni ronisati sation. on. In this this type type of flow flow devid devider er numb number er of smal smalll gear pumps of o f equal discharge are assembl asse mbled ed with single spiddle or shaft. Their suction su ction is also common. Hence when they rotate, rot ate, they t hey supply equal amount of o f oil from all the pumps, which are supplied to each actuator. Visit Visit the website __www.vivolo.co __www.vivolo.com_ m_ who is manufacture manufacturerr of such valve, to understand underst and them throughly. throughly. (Ref. page no. 36-49) These valves also give good accuracy. But as load on individual cylinder various, variation in stroke is bound to happen. Hence correction of error erro r at the t he end of stroke is unavoidable. unavoidable.

Nu mber mb er o f smal sm alll g ea r pum p um ps w it h c o mmo n sucntion and individual discharge for equally dividiing main pump discharge.(These pumps are not connected to electric motor. But only seves as flow divider. they also could be considered as hydraul hydraulic ic gear motor)

Pump coupled to motor for supplying supplying oil oil under pressure to system. M

Figure No 10.21.2


10-56



Synchronisation circuits for two cylinders. Synchronisation of o f two cylinders is possible by using using flow control cont rol valve and tedium pump as discussed earlier ear lier.. Few special circuits are also possibl po ssiblee to achieve synchronisation; some of them are as follows. Diamond circuit: - In this circuit circuit two t wo flow control contro l valves valves are used to t o control co ntrol speed of two cylinders cylinders in both directions. But forward and reverse speed could not be adjusted and selected separately. separately. Also during up stroke stro ke the control contr ol is meter-in and during down stroke, it is meter-o meter-out. ut.

To increase accuracy, one flow flow control co ntrol valve could be replaced with proport pro portional ional electro-hydraulic flow control contro l valve. valve. This valve senses the variation and a nd adjusts the t he flow flow to t o achieve ac hieve high high accuracy accurac y.

M

Doamond Circuit Figure No 10.21.3


10-57



Steel plate

Pully

Moveable element

Sensor of servo Valve

Servo Valve For Synchronisation

M

P

Synchronisation by serro -valve Figure No 10.21.4


10-58


Circuit Diagram of Drill

10.22 Circuit Diagram of Drill Pump:A variable variable discharge pump is used so that as load increases, speed decreases and when dr dril ills ls get jamm jammed ed due to any reason it stops rotating. rotating. Reduced Reduced or no discha discharge rge from variabl variablee displ displacem acement ent pump pump at high high pressure pressure safe safe guard agains againstt oil heatin heating. g. Direction control valve :Advantage of using three positions p ositions all port block valves is that at neutral position cylinder cylinder remains locked, and it does not drain-out system pressure. Flow control valve : By using using flow control contro l valve valve we control contro l spindle spindle approach appro ach and return retur n speed. Four-way-two Four-way-two position po sition direction cont control rol valve :Because of two positions, cylinder will either clamp or un-clamp. Circuit is designed in such a way that when whe n solenoid valve un-energised un-energ ised it remains remains in clamp clamp position. These safeguards sa feguards accidental ac cidental released of job. displacement ent pump pu mp against sudden over loading loading and accesses Check valves safeguards variable displacem pressure pressure generated generated in cyli cylinde nders. rs. pr essure should shou ld not J-type direction cont control rol valve valve  is used for drill head feed cylinder, so that pressure be locked in pipe line line of cylinder cylinder.. Locked Locked pressure may actuate the pilot pilot operated check valve valve which holds spindle in lifted lifted condition. cond ition. Counter balance valve  develops a back pressure, pre ssure, because of o f which which drill head does not no t over travel due to weight of spindle. spindle. Because of counter balance balance valve, valve, flow control contro l valve valve also works wor ks accurately. Pilot operated check valve  Drill Head feed Cylinder locks drill head feeding feeding cylinder cylinder Clamp Cylinder Lift Cylinder in position, so that t hat when drill dr illing ing Unclamp clamp 8 stops, spindle remain stationery Up 2 Down and do not slides down due to 10 own weight. 4 3 Reducing valve  is used to reduce pressure supplied to up7 2 down cylinder withou withoutt reducing system pressure. Meter-out type flow control con trol 6 valve  is used to control spindle spindle speed.Meter-out type 9 valve reduces fluctuation in speed much better than meter5 in type circuit,with change in 5 cutting load. 1

M

Figure No 10.22.1


10-59


Honning

10.23 Honning What is honning? Honing is simil similar ar to internal grinding, grinding, but in this process instead instea d of grinding wheel grinding stone sticks are used and a nd grinding grinding stone st one sticks are rotated rotat ed as well as reciprocated inside inside an cylindrical cylindrical object to remove material of object as per requirement. In honing, ovality ovality as well as taper of inside inside diameter diameter is corrected. correct ed. As per the size and grade of honing honing stone sto ne stick used for honing honing we get surface finish finish better than t han grinding process. Honing process proc ess is generally used iin n manufacturing of hydraulic cylinder cylinder or cylinder of aut automo omobil bilee engine. flow High flow high pressure pump :- To reciprocate honing head at required high speed high flow pump pump is used as per requireme requirement. nt. Relief valve  regulates pressure of reciprocating cylinder. contr ols the speed of reciprocat ing cylin cylinder. der. Flow control valve controls Direction control valve  controls contr ols the direction of reciprocating recipro cating cylinder. cylinder. This simple counter balance valve  offers some back pressure pressur e when cylinder cylinder descends down, do wn,

HONNING 14

11

6 5 10 13

9 4

12 8 3

1 2

P

7

M

P

Figure No 10.23.1

because because of this this speed speed of cyli cylinder nder remai remains ns under under control as per flow control control valve valve setting. setting. Reciprocating cylinder : - In honing machine machine up and a nd down speed of honing head should be same, hence either cylinder in mode double ended. Or differential cylinder is used along with regenerative regenerat ive circuit. circuit. Pump with low discharge is used for hydraulic motor o f honing head, as revolving speed of honing head is between betwe en 10-70 10-7 0 rpm only, only, and clampi c lamping ng cylinder is is operat ope rated ed only at the beginni be ginning ng and at the of operation. operation. Relief valve  controls contro ls working pressure of pump No. 7


10-60


Honning

Direction control valve  and 12 are used in series because because of two reasons. a) Flow Flow is small hence heat heating ing will will be minimum. minimum. b) Clam Clampi ping ng cyli cylinder nderss are rarely rarely used, hence hence it does not interf interfere ere func function tionin ing g of hydraul hydrauliic motor. motor. If we use all port block valve valve in such situation, then one more valve valve we have to add to unload pump when both hydraulic motor and clamping clamping cylinder cylinder are not in use. Hence by using two direction direct ion control cont rol valve in in series we save one valve. va lve. cont rols and varies the speed of hydraulic hydraulic moto motorr attached attac hed to honing head. Flow control valve , controls Hydraulic Motor 11 :- rotates rot ates the honing head. By using using hydraulic motor moto r in place of general geared electric moto motor, r, we have full and easy control over speed and torque torq ue of honing honing head. Pilot operated check valve 13 locks the t he clamping clamping cylinder cylinder under pressure. Clamping cylinder 14 holds the job firmly, firmly, as in honing job is subjected to rotary rot ary torque to rque as well we ll as up and a nd down pulli pu lling ng and pushing force. In this hydraulic hydraulic circuit we have used meter in type flow flow contro c ontroll valve. valve. Bleed of o f type is is also used. use d. In bleed-off power loss is comparatively less.


10-61


CIRCUIT DIAGRAM OF

SURFACE GRINDING MACHINE Table slide cyl.

clamp cyl .

Lubrication

Ø 100 x Ø 75 x 5000mt

Lub.Return

20 kg/cm

20kg/cm

7/min

0.5 2kg/cm M

7.5kw

95/min

500 Figure No 10.23.2


10-62

Volume.5. Study of Hydraulic Circuits

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