API Pump Theory

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Pump Theory API Reciprocating Displacement Displacem ent Pumps Pumps.. Steve Digby SPX Process Equipment Limited Bran+L Bran+Lueb uebbe be Operat Operation ion U.K. U.K.

SPX Process Equipment

2003

WCB-Flow Products

2002

GD Engineering Engineering

2005 Plan Employees 2585

OFM Oilfield Fabricating & Machine After Market & Field Services

SPX Process Equipment

2003

WCB-Flow Products

2002

GD Engineering Engineering

2005 Plan Employees 2585

OFM Oilfield Fabricating & Machine After Market & Field Services

Pump Theory API Reciprocating Displacement Pumps

Topics • • • • •

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Pump Theory API Reciprocating Displacement Pumps • API stands for American Petroleum Institute • API 674 and 675 are widely used as an industrial standard for reciprocating displacement pumps. • Mainly used in Petroleum, Chemical Processing, and Oil&Gas Industry. • Describes and specifies constructional design, qualification criteria, and how pumps and documentation shall be executed.


Reciprocating metering/dosing pumps deliver a controlled & accurate flow to predetermined points of a process independent of pressure.


API 675 Metering Pump With Diaphragm Pumphead

API 674 Reciprocating Triplex Pump With Diaphragm Pumpheads


Metering Pump Equation V=A.h.n V = theoretical Volumetric flow of the metering pump A = plunger square area h = stroke length n = stroking speed (stroke frequency)

Positive Displacement Pumps Reciprocating Definition (in accordance with API Standard 674) There is no actual definition in the standard other than highlighting the difference between a Power Pump & Direct Acting Pump. Essentially these pumps transmit a predetermined mass flow at medium to high pressure.

Pumps are normally configured in Triplex, Quintuplex and Septuplex designs.

Positive Displacement Pumps Controlled Volume Definition (in accordance with API Standard 675) “A controlled volume pump is a reciprocating pump in which precise volume control is provided by varying effective stroke length”.

• Such pumps are also known as metering, proportioning, chemical injection, dosing, or controlled volume pump . • These pumps deliver a controlled & accurate flow to predetermined points of a process independent of pressure.

Pump Theory API Reciprocating Displacement Pumps Typical Deviations to API 675 API Listing 1.5 Equipment offered is referring to German and European standards i.e. DIN, EN, IEC, ISO,.... 2.2.5.1 Details of threading conform to ISO. 2.12.3 Unless proposed differently visual indication of capacity setting is shown as actual stroke length. 2.13.1.13 Bolts are calculated and selected in accordance with German pressure vessel code (AD-Merkblätter). 3.1.7 Motors are flanged directly to the pump. Consequently, there is no need for jackscrews. 3.3 Metering pumps are suitable for mounting directly onto prepared concrete. Base plates are therefore optional and can be quoted at additional cost. 3.3.9 If not stated differently base plates will not be furnished with jackscrews. 3.4.3.2 If not stated differently single point terminal box for instrumentation is not included. 3.4.4.3 The gauges used for local diaphragm rupture indication have dials either 63 mm or 100 mm, depending on size of pumphead. 3.4.5 Electrical systems are not included unless expressly required and specifically quoted.

Pump Theory API Reciprocating Displacement Pumps API Data Sheet – Purchaser Information 1 2 3 4 5 6 7

For: No. of motors required 1 Site Serial no. TBA Remarks Notes : O indicates information to be completed by Purchas e  indicates information to be completed by manufacturer. API standard 674 governs unless otherwise noted OPERATING CONDITIONS (to be completed by purchaser)

8 9 10 11 12 13 14 15

Liquid (HC) Condensate Pumping temperature (°C) PT: Normal 19 Maximum Minimum -9 Density @ PT (kg/m³): 569,8 Vapor pressure @ PT (bar): Viscosity @ PT (cP): 0,16 Acceleration head (m) Note 1 NPSH available (m): 14,7

Capacity @ PT (m³/h): Maximum Note 2 Minimum N Rated 5,3 Discharge pressure (bar g): Maximum Minimum Rated Note 4 Suction pressure ( bar g): Maximum Minimum Rated 17,8 Differential pressure (bar g): Maximum 19,2 Minimum Rated 16,2


Installation Considerations & How to Avoid Problems

Pump Theory API Reciprocating Displacement Pumps Flow Pattern of various Pumps Types

Simplex Pump Duplex Pump Triplex Pump Centrifugal Pump

Pump Theory API Reciprocating Displacement Pumps What we are Trying to Avoid Suction Side • Insufficent NPSHA • Pump Starvation • Cavitation

Discharge Side • Insufficent Flow • Over Pressure • Pipe Hammer

General Poor Pump Operation In almost all cases of insufficient flow rate or frequent service calls the pump will be blamed, not the system Only Recognised as Problems During Commissioning or Initial Operation.

Pump Theory API Reciprocating Displacement Pumps Many Installations Are Designed On Smooth Flow Conditions & Ignore Factors Such as:• Reciprocating Pumps Generate a Pulsating Flow • ~3x Equivalent Smooth Flow. • Line Losses Can be High. • Crucial on Critical Applications i.e. Liquid Gases, High Temperature, Volatile Liquids.

Pump Theory API Reciprocating Displacement Pumps Flow Pattern of a Single Head Pump 100 % Capacity setting 60 % Capacity setting Top dead Center

e g r a h c s i D

Bottom dead Center n o i t c u S

Bottom dead Center

Pump Theory API Reciprocating Displacement Pumps Two Major Factors That Can Adversely Affect The Operation of Reciprocating Pumps Buy Are Often Overlooked are: •Friction Losses Higher Viscosity Applications Pressure Required to ensure that the liquid flows continually in the system during the maximum demanded flow volume. Low Viscosity Application

•Mass Acceleration Losses Pressure Required to cause the liquid to move at the beginning of each plunger stroke •Both Have a high impact on NPSHA . •Only the higher of the two values is considered. •On reciprocating pumps this is generally Mass Acceleration.

Pump Theory API Reciprocating Displacement Pumps Factors Affecting Mass Acceleration Pressure • Plunger or Piston Diameter. • Stroke Length • Internal Pipe Diameter & Overall Length. • Pump Speed. • Pump Configuration (Single or Multi Head) Example. Single Head Pump 20mm Dia Plunger x 20 mm Stroke Length Operating Speed 100 Strokes/Min Fitted To 8mm NB Pipe Mass Acceleration Pressure = 0.84 m/m Pipe Length = 10m ∆P = 8.4m or 0.84 Bar

Pump Theory API Reciprocating Displacement Pumps Net Positive Suction Head Net positive suction head (NSPH) is the total inlet pressure, stated in meters head minus the vapor pressure of the liquid in meters


What is a System ? (in terms of the issue “NPSH”) Suction vessel

p(abs) or Habs

A system is normally composed of: • a pump • a vessel from which the pump takes the liquid (suction vessel) • piping between pump and suction vessel including valves, elbows, strainers, etc. L (Length of suction piping)

Pump

Hst (Static head)

d (pipe inside diameter)

Pump Theory API Reciprocating Displacement Pumps Mass Acceleration Forces

Simplex Pump Duplex Pump Triplex Pump Centrifugal Pump

Pump Theory API Reciprocating Displacement Pumps Net Positive Suction Head Available NPSHA is a property of the system & determined by the purchaser! Net Positive Suction Head Required NPSHR is a property of the pump and is the minimum pressure required, measured at the suction flange , to prevent cavitation. For satisfactory pump operation NPSHA should always exceed NPSHR by a minimum of *1 -2 m *(varies for different pump types and suppliers)

Pump Theory API Reciprocating Displacement Pumps Total head

The NPSH concept Head of vapor pressure

Head of friction losses

Head in suction vessel (above liquid level)

Head of mass acceleration losses

NPSHA Static head

NPSHR

NPSH margin

Pump Theory API Reciprocating Displacement Pumps How can NPSHA be calculated ? The calculation is no more than determining the difference between • positive heads i.e. absolute head in suction vessel plus static head and • negative heads (losses) i.e. head due to vapor pressure, friction and mass acceleration

NPSHA = H +Hst - Hvp - ΣHfr - Hma

Pump Theory API Reciprocating Displacement Pumps Inadequate NPSHA Will Cause Cavitation Leading To: • Erratic Performance • Reduced Flow • Erosion in The Plunger Packing Area and Non Return Valves • A Lot of Noise!!! • Cost Non Return Valves

Plunger Sealings

Pump Theory API Reciprocating Displacement Pumps Considerations to Maximise The NPSHA of the System • Minimise the pipe length • Maximise the bore diameter • Minimise no of bend, tees and valves etc. • Use of Pulsation Dampening Devices • Increase Pressure (Booster Pump, Nitrogen Blanket, Static Head etc). • Use of a multi head pump. • Adequate Pipe Supporting

Pump Theory API Reciprocating Displacement Pumps Pulsation Dampeners

Pump Theory API Reciprocating Displacement Pumps Pulsation Dampener Affect


Overall Cost of Ownership

Comparison of the investment and maintenance costs of a hydraulically actuated diaphragm pump compared to a packed plunger pump Process Fluid Flowrate

Process Pressure Operating Hours

: Methanol : 12m3 /hr

: 160 bar : 8000/year

Diaphragm Pump

Packed Plunger Pump

Triplex

Triplex

250,000

150,000

Annual Spare Use - plungers

None

6 x 3,000 = 18,000

- plunger packing

3 x 500 = 1,500

12 x 1,000 = 12,000

- diaphragms

3 x 1,000 = 3,000

None

- pump valves

6 x 2,000 =12,000

6 x 2,000 = 12,000

- labour costs

10 h x 150 = 1,500

50 h x 150 = 7,500

18,000

40,500

Maintenance costs after 3 years operation

63,000 Inc 1 set of plungers

148,500

Total costs after 3 years operation

313,000

298,500

Pump Type Investment Cost

Annual maintenance costs

Comments Energy costs Lubrication of Plunger Packing Leakage

~5% Lower Not Required None

Packing Friction Necessary Needs to be contained

API Pump Theory

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