3.2 Hydraulic Cylinder

3.2. Hydraulic cylinders and cushioning devices

2012

3.2. Hydraulic Hydraulic cylinders cylinders and cushioning cushioning devices devices 3.2.1. Introduction Hydraulic cylinders convert fluid flowing under pressure to a linear motion. They are singleacting and returned by either a spring or the force of gravity acting on the load, or they are double-acting and have fluid piped to both ends of the piston. Single-acting cylinders with large bore-to-diameter ratios are called rams. Figure 3.2.1 illustrates how cylinders and cushioning devices are classified. The force exerted by a hydraulic cylinder is proportional to the cross section area of the piston and the pressure of the fluid. Double-acting cylinders that have the rod extending through both end caps exert the same force in both directions.

Cylinders with single-end rods exert greater force when the cylinder extends. The difference in force between the two is accounted for by the difference in area between both sides of the piston. Cushioning devices decelerate the load to prevent shocks that could damage cylinders and other equipment. Cylinder cushioning devices use a tapered or stepped rod that enters a sleeve mounted in the end caps of the cylinder as it nears the end of the stroke. A typical hydraulic shock absorber cushions bumping loads with a spring-returned hydraulic cylinder that forces the fluid through an adjustable orifice when the load strikes the end of the rod.

Figure 3.2.1 Actuator classification.

Hydraulic and pneumatic control lecture notes by Siraj K.

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Cylinder actuators are defined by their ability to exert a linear force and hold it at any specified position indefinitely. Several factors are used to select hydraulic cylinders, including: • Purpose of the cylinder • Construction Construction • Required force • Temperature • Load • Duty cycle • Mounting • Acceleration and deceleration forces The purpose of the cylinder describes its type. The cylinder may move a load resistance in one direction only with a gravity or spring return, or move it in both directions under pressure, or have equal velocities as it travels in both directions. Cylinders, then, may be of the single-acting type, double-acting type or have a double-end rod, "DER," to equalize the areas on both side s of the piston and add support. If the cylinder piston is connected to a single-end rod, it is considered to be of a hydraulically unbalanced design. Double-end rod cylinders are considered to be hydraulically balanced because both sides of the piston have the same area. Tandem balanced cylinders exert twice the force available from single piston cylinders by providing twice the effective piston area in two chambered spaces.

3.2.2. Hydraulic cylinders operating features

A cylinder is a hydraulic actuator that is constructed of a piston or plunger that operates in a cylindrical housing by the action of liquid under pressure. Cylinder housing is a tube in which a plunger (piston) operates. In a ram-type cylinder, a ram actuates a load directly. In a piston cylinder, a piston rod is connected to a piston to actuate a load. At the end of a cylinder from which a rod or plunger protrudes is a rod end. Its opposite end is the head end. The hydraulic connections are a head-end port and a rod-end port (fluid supply).

Hydraulic cylinders are constructed of a cylinder barrel, piston and rod, end cap s, ports, and seals (Fig.3.2.1). The piston provides the effective area against which fluid pressure is applied and supports the piston end of the rod. The opposite end of the rod is attached to the load Hydraulic and pneumatic control lecture notes by Siraj K.

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resistance. The cylinder bore, end caps, port s, and seals maintain a fluid tight chamber into which fluid energy is piped. Routing of the fluid determines whether the cylinder extends or retracts. A common feature added to a cylinder is a mechanism called a cushioning device, dashpot, snubber, or decelerator to reduce shock loads that would be caused by bottoming the piston in either extreme stroke position. Cylinders referred to as rams use large cylinder rod s approaching the size of the cylinder bore to give maximum support to the load end of the rod. They are used extensively in such single-acting applications as car hoists , dump cylinders , and hydraulic presses.

Figure 3.2.1 Cylinder components (courtesy of Tomkins-Johnson Company).

(a)

Single-acting cylinder.

This cylinder has only a head-end port and is operated hydraulically in one direction. When oil is pumped into a port, it pushes on a plunger, thus extending it. To return or retract a cylinder, oil


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must be released to a reservoir. A plunger returns either because of the weight of a load or from some mechanical force such as a spring. In mobile equipment, a reversing directional valve of a singleacting type controls flow to and from a single-acting cylinder.

Figures 3.2.2 and 3.2.3 illustrate the construction of single-acting hydraulic cylinders. The piston, or plunger, is driven hydraulically in one direction. In the other direction, the piston moves under the action of an external force or a built-in spring.

Figure 3.2.2 Single-acting plunger-type cylinder, returned by external force.

Figure 3.2.3 Single-acting piston-type cylinders, spring returned.

A single-acting, piston-type cylinder uses fluid pressure to apply force in one direction. In some designs, the force of gravity moves a piston in the opposite direction. However, most cylinders of this type apply force in both directions. Fluid pressure provides force in one direction and spring tension provides force in the opposite direction. Most piston-type cylinders are double acting, which means that fluid under pressure can be applied to either side of a piston to provide movement and apply force in a corresponding direction. This cylinder contains one piston and piston rod assembly and operates from fluid flow in either direction. The two fluid ports, one near each end of a cylinder, alternate as inlet and outlet, depending on the directional-control valve flow direction. This is an unbalanced cylinder, which means that there is a difference in the effective working area on the two sides of a piston. A cylinder is normally installed so that the Hydraulic and pneumatic control lecture notes by Siraj K.

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head end of a piston carries the greater load; that is, a cylinder carries the greater load during a piston-rod extension stroke.

(b)

Double-acting cylinder.

This cylinder must have ports at the head and rod ends. Pumping oil into the head end moves a piston to extend a rod while any oil in the rod end is pushed out and returned to a reservoir. To retract a rod, flow is reversed. Oil from a pump goes into the rod end, and the head-end port is connected to allow return flow. The flow direction to and from a double-acting cylinder can be controlled by a double-acting directional valve or by actuating control of a reversible pump.

The piston of a double-acting hydraulic cylinder is driven hydraulically in both directions of motion. This cylinder may be single rod (Fig. 3.2.4), twin-rod symmetrical (Fig. 3.2.5), or twinrod nonsymmetrical (Fig. 3.2.6). The twin-rod cylinder is said to be symmetrical if the diameters of the piston rods are equal. It is usually used in hydraulic servo systems.

Figure 3.2.4 Single rod cylinders.


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Figure 3.2.5 Twin-rod symmetrical cylinders

Figure 3.2.6 Twin-rod nonsymmetrical cylinders.

c) Tandem Cylinders

The tandem cylinder duplicates the pressure force, for the same barrel diameter (see Figs. 3.2.7 and 3.2.8).

Figure 3.2.7 a differential tandem cylinder.

In a differential cylinder, the areas where pressure is applied on a piston are not equal. On a head end, a full piston area is available for applying pressure. At a rod end, only an annular area is available for applying pressure. The area of a rod is not a factor, and what space it does take up reduces the volume of oil it will hold. Two general rules about a differential cylinder: with an Hydraulic and pneumatic control lecture notes by Siraj K.

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equal GPM delivery to either end, a cylinder will move faster when retracting because of a reduced volume capacity. With equal pressure at either end, a cylinder can exert more force when extending because of the greater piston area. In fact, if equal pressure is applied to both ports at the same time, a cylinder will extend because of a higher resulting force on a head end.

Figure 3.2.8 a symmetrical tandem cylinder.

c) Three-Position Hydraulic Cylinders Some of the operating organs may have three operational positions. In this case, the ordinary double-acting hydraulic cylinder does not give the required controllability. Figure 3.2.9 shows the typical construction of a three-position cylinder. The cylinder has two separate pistons and piston rods. The three positions are obtained by pressurizing the cylinder chambers, as shown in the table in Fig. 3.2.9.

Figure 3.2.9 Operation of a three-position cylinder. (Note: P and T are the pressure and tank lines.)

d) Telescopic Cylinders Telescopic cylinders are used in industrial and mobile equipment hydraulic systems. This class of cylinders provides long cylinder strokes with relatively small installation space. The telescopic cylinder may be either single acting (Fig. 3.2.10) or double acting (Fig. 3.2.11). If the Hydraulic and pneumatic control lecture notes by Siraj K.

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pressure affects the pistons via port A, they travel outward one after another. The double-acting cylinder retracts by pressurizing the port B.

Figure 3.2.10 Single-acting telescopic cylinders. ( Courtesy of Bosch Rexroth AG.)

Figure 3.2.11 Double-acting telescopic cylinders. ( Courtesy of Bosch Rexroth AG.)

3.2.3. Cylinder mounting and mechanical linkages Various types of cylinder mountings are in existence, as illustrated in figure 3.2.12. This permits versatility in the anchoring of cylinders. The rods ends are usually threaded so that they can be attached directly to the load, a clevis, a yoke or some other mating device. Through the use of various linkages, the applications of hydraulic cylinders are limited only by the ingenuity of the fluid power designer. As illustrated in figure 3.2.13, these linkages can transform a linear motion into either an oscillating or rotary motion. In addition, linkages can also be employed to increase


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or decrease the effective leverage and stroke of a cylinder. Much of efforts have been made by manufacturers of hydraulic cylinders to reduce or eliminate the side loading of cylinders created as a result of misalignment. It is almost impossible to achieve perfect alignment even through of a hydraulic cylinder has a direct bearing on its life.

Figure 3.2.12. Various cylinder mountings


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Figure 3.2.13 typical mechanical linkages that can be obtained with hydraulic cylinders.


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Eye or Clevis Cylinder Mounting

Figure 3.2.14 illustrates the possible combinations of mounting a plane bearing and a spherical bearing at the cylinder cap and rod eye.

Figure 3.2.14 Eye or clevis cylinder mounting. ( Courtesy of Bosch Rexroth AG.)

Trunnion Mounting

The trunnion mounting allows angular movement of the cylinder and a shorter retraction length (see Fig. 3.2.15).

Figure 3.2.15 Trunnion mounting. ( Courtesy of Bosch Rexroth AG.)

Flange Mounting

The flange mounting is preferred for vertical cylinder mounting. When the cylinder is loaded mainly by thrust force (tension or compression), the mounting bolts at the flange should be unloaded. The mounting positions shown by Fig. 3.2.16 are recommended for this purpose. Hydraulic and pneumatic control lecture notes by Siraj K.

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Figure 3.2.16 Flange mounting. ( Courtesy of Bosch Rexroth AG.) Foot Mounting

The foot mounting of hydraulic cylinders is illustrated in Fig. 3.2.17. The mounting bolts should be protected against shear stress. Therefore, thrust keys are provided to absorb the cylinder forces as shown.

Figure 3.2.17 Foot mounting. ( Courtesy of Bosch Rexroth AG.)

A universal alignment mounting accessory designed to reduce misalignment problems. By using of these accessory components and a mating clevis at each end of the cylinder, the following benefits are obtained: •

Freer range of mounting positions

•

Reduced cylinder binding and side loading

•

Allowance for universal swivel

•

Reduced bearing and tube wear


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3.2. Hydraulic cylinders and cushioning devices •

2012

Elimination of piston blow-by caused by misalignment

3.2.4. Cylinder force, velocity, power and loads due to moving of weights The out put forces (F) and piston velocity (v) of doubling acting cylinders are not the same for extension and retraction strokes. This explained as follows (in conjunction with figure 3.2.3): During the extension stroke, fluid enters the blank end of cylinder through the entire circular area of the piston (A p). However during the retraction stroke, fluid enters the rod end through the smaller annular area between the rod and cylinder bore A p

− Ar

, where A p equals the piston

area and Ar equals the rod area. This difference in flow path cross-sectional area accounts for the difference in piston velocities. Since A p is greater than ( A p

− Ar

),

the retraction velocity is

greater than the extension velocity for the same input flow rate.

Figure 3.2.18. The effective area of double-acting cylinders is greater for extension stroke than it is for the retraction stroke


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Similarly during the extension stroke, fluid pressure bears on the entire circular area of the piston. However, during the retraction stroke, fluid pressure bears only on the smaller annular area between the piston rod and cylinder bore. This difference in area accounts for the difference in output forces. Since A p is greater than ( A p

− Ar

),

the extension force is greater than the

retraction force for the same operating pressure. Equations (3.2.1) through (3.2.4) allow for the calculation of the output force and velocity the extension and retraction strokes of 100% efficient double-acting cylinders.

Extension stroke

3.2.1

F ext = p ∗ A p

v ext

=

Qin

3.2.2

A p

Retraction stroke F ret

= p ∗

v ret

=

( A

A p

Qin

p

3.2.3

− Ar

− Ar

3.2.4

)

Where AP = Piston area, m

2

Ar = Rod-side area, m

2

F ext = extension force, N F ret = retraction force, N p = Pressure, Pa v = Piston speed, m/s 3

Qin = Flow rate, m /s

The output force required from a hydraulic cylinder and the hydraulic pressure available for this purpose determine the area and bore of the cylinder. For a required force and given pressure, Cylinder area

π d b2 4

=

=

Force

Pr essure

F p


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d b

=

2012

4 F π p

Where the bore ( d b ) is computed in (in), (mm), the force (F) is in lbf (N), and the pressure (p) is 2

in lbf/in (Pa or bars).

The power developed by a hydraulic cylinder equals the product of its force and velocity during a given a stroke. Using this relation and equations (3.2.1) and (3.2.2) for the extending stroke and equations (3.2.3) and (3.2.4) for the retraction stroke, we arrive at the same result: power = p ∗ Qin . Thus, we conclude that the power developed equals the product of pressure and

cylinder input volume flow-rate for both the extension and retraction strokes.

The horsepower developed by a hydraulic cylinder for either the extension or retraction stroke can be found using equation (3.2.5). Power (kW ) =

v p ( ft / s ) ∗ F (lb )

=

Qin ( gpm ) ∗ p ( psi )

550

1714

3.2.5

Using metric units, the kW power developed for either the extension or retraction stroke can be found using equation (3.2.5M). Power (kW ) = v p (m / s ) ∗ F (kN ) = Qin (m 3 / s ) ∗ p(kPa )

3.2.5M

3

Q = Flow rate, m /s 3

QL = Internal leakage flow rate, m /s

Note that the equating of the input hydraulic power and out put mechanical power in equations (3.2.5) and (3.2.5M) assumes a 100% efficient hydraulic cylinder.

3.2.5. Cylinder loadings through mechanical linkages In many applications, the load force that a hydraulic cylinder must overcome does not act along the axis of the hydraulic cylinder. Because of this, the load force and the hydraulic cylinder force are not equal. Therefore, it is necessary to analyze how to determine hydraulic cylinder forces Hydraulic and pneumatic control lecture notes by Siraj K.

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required to driven on-axial loads. Accordingly, we can classify the mechanical linkages into first–class, second-class and third-class lever systems.

First-class Lever System First-class lever system is characterized by the lever fixed-hinge pin being located between the cylinder and the load rod pin. To determine the cylinder force F cyl required to drive a load force Fload, we equate moments about the fixed hinge, which is the pivot point of the lever. The cylinder force attempts to rotate the lever counterclockwise about the pivot and this creates a counterclockwise moment. Similarly, the load force creates a clockwise moment about the pivot. At equilibrium, these two moments are equal in magnitude:

Therefore, counterclockwise moment = clockwise moment F cyl ( L1 cos θ ) = F load ( L2 cos θ )

Or F cyl

=

L2 L1

F load

3.2.6

It should be noted that the cylinder is clevis-mounted to allow the rod

Figure 3.2.19. Use of first-class lever to drive a load


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Since the cylinder is clevis-mounted, it allows the rod-pinned end to travel along a circular path as it rotates about the fixed-hinge pin. If the centerline of the hydraulic cylinder becomes offset by an angle ϕ from the vertical, we have,

F cyl ( L1 cos θ ∗ cos φ ) = F load ( L2 cos θ )

Or F cyl

=

L2 L1 cos φ

F load

3.2.7

Examination of equation (3.2.6) shows that L 1 (distance from cylinder rod to hinge pin) is greater than L2, the cylinder force is less than the load force. Of course, this results in a load stroke that 0 is less than the cylinder stroke, as required by the conservation of energy law. When ϕ is 10 or 0

0

less, the value of cos ϕ is very nearly unity. (cos 0 = 1, and cos 10 = 0.985)and thus equations (3.2.6) can be used instead of equation (3.2.7).

A length of moment arm for either the cylinder force or load force is the perpendicular distance from the hinge pin to the line of action of the force. Thus, for the development of equation (3.2.6), the moment arms are L1cos

θ

and L2 cos

θ

rather than simply L 1 and L2. Similarly, for

the development of equation (3.2.7), the moment arm for the cylinder force L 1cos

θ

x cos ϕ,

0

rather than simply L1 cosθ, which is based on the assumption that cos ϕ = 0 .

Second-class Lever System Figure 3.2.20 shows a second-lever system, which is characterized by the load rod pin being located between the fixed-hinge pin and cylinder rod pin of the lever. The analysis is accomplished by equating moments about the fixed-hinge pin, as follows: F cyl cos φ ( L1 + L2 ) cos θ = F load ( L2 cos θ )

Or

F cyl

=

L2

( L1 + L2 ) cos φ

F load


3.2.8

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Figure 3.2.20. Use of second-class lever to drive a load

Comparing equation (3.27) to equation (3.2.8) shows that a smaller cylinder force is required to drive a given load force for a given lever length if a second-class lever is used instead of a firstclass lever. Thus, using a second-class lever rather than a first-class lever reduces the required cylinder piston area for a given applications. Of course, using a second-class lever also results in a smaller load stroke for a given cylinder stroke.

Third-class lever system As shown in figure 3.2.21, for a third-class lever system the cylinder rod pin lies between the load rod pin and fixed-hinge pin of the lever. Equating the moments about the fixed-hinge pin yields F cyl cos φ ( L2 cos θ ) = F load ( L1 + L2 )cos θ

Or F cyl

=

L1 + L2 L2 cos φ

F load

3.2.9

An examination of equation (3.2.9) reveals that for a third-class lever, the cylinder force is greater than the load force. The reason for using a third-class lever system would be produce a Hydraulic and pneumatic control lecture notes by Siraj K.

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load stroke that is greater than the cylinder stroke, at the expense of requiring a larger cylinder diameter.

Figure 3.2.21. Use of third-class lever to drive a load

3.2.6. Hydraulic cylinder cushions and shock absorber Double acting cylinders are of ten provided cylinder cushions at the two ends to slow down the piston near the ends of stroke. This prevents excessive impact when the piston is stopped by the end caps, as illustrated in figure 3.2.22. As shown, deceleration starts when the tapered plunger enters the opening in the cap. This restricts the exhaust flow from the barrel to the port.

During the last small portion of the stroke, the oil must exhaust through an adjustable opening. The cushion design also in corporate a check valve to allow free flow to the piston during direction reversal. The maximum pressure developed by cushions at the ends of a cylinder must be considered since excessive pressure build up would rupture the cylinder.


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Figure 3.2.22. Operation of cylinder cushions

When cylinders reach the end of their stroke, the pressure rises quickly, creating a shock wave in the hydraulic circuit. Cushioning is done to reduce this stock. The concept, shown in Fig. 3.2.23, is quite simple. First, we consider the case in which the cylinder is retracting. The spear closes off the large opening where the fluid is exiting the cap end of the cylinder. Fluid must now flow out the small opening past a needle valve. This valve adjusts the orifice and sets the back pressure that develops in the cap end. The resultant force slows the piston so that it “coasts” to a stop. The resultant pressure shock in the main circuit is significantly reduced. The same technique is used to cushion the cylinder when it is extending. In this case, a sleeve is mounted on the rod to close the main opening so that flow goes through the orifice.


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Figure 3.2.23. Schematic showing a technique for cushioning a hydraulic cylinder.

To understand cushioning, it is appropriate to review a basic principle of fluid power. Always ask the question, what is happening at the relief valve? We will consider the case where a fixed displacement pump is supplying the flow to extend the cylinder. When the spear closes the large opening, the fluid must flow past the needle valve. The resultant pressure drop increases the back pressure on the rod end. The pump must build a higher pressure on the cap end. This cap end pressure must build to the point where the relief valve cracks open before the cylinder will slow. Remember, a fixed displacement pump puts out a given volume of oil for each revolution. Neglecting pump leakage, this oil either goes to the cylinder or through the relief valve. The adjustments made to the needle valve on the cylinder interact with the characteristics of the relief valve (and to a lesser degree with other components in the circuit) to produce a given deceleration rate.

A number of techniques have been developed to cushion cylinders. Large cylinders are cushioned with some type of stepped procedure that decelerates the piston in increments. Manufacturer’s literature can be referenced for the back-pressure curves generated by these


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techniques. The ANSI symbol for a cylinder cushioned on both ends is given in Fig. 3.2.24. The arrow through the cushion block indicates that the cushioning is adjustable.

Figure 3.2.2 ANSI symbols for single and double rod cushioned cylinder

Cushioning devices are provided in the ends of hydraulic cylinders or as separate units when loads must be decelerated. Hydraulic shocks to the cylinder and system are reduced by slowing down the piston just before it contacts the cylinder end caps. The sleeve or spear-type cushioning device is often used as the decelerating mechanism. The energy absorbed by decelerating a body in motion is converted to heat and dissipated to the environment through the fluid and cylinder body.

Refer to Fig. 3.2.25 as the piston completes its extension stroke, the slightly tapered end cushioning sleeve enters the rod end cap blocking the normal flow of fluid. The flow of fluid is then rerouted through the bypass port and needle valve at a controlled rate, decelerating the piston. Cushioning at the head end of the cylinder during the retraction stroke is accomplished in the same manner by the action of the tapered cushioning spear plunger as it enters the end cap. This blocks the normal flow of fluid and causes fluid to be rerouted through the bypass port and metering valve to decelerate the piston. The check valve, shown only on the blank end of the


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cylinder, is used to direct fluid at system pressure to the full area of the piston during acceleration.

Figure 3.2.25. Cylinder cushioning devices (courtesy of Carter Controls. Inc.).

Figure 3.2.26 shows a hydraulic cylinder with an adjustable cushioning element. The piston (1) is fitted with a conical end-position cushioning bush (spear) (2). During the cylinder retraction stroke, the returned oil flows freely to the return line. When approaching the end position, the spear enters a cylindrical cave in the cylinder cap (4).

Figure 3.2.26 (a) Cushioning of hydraulic cylinders. ( Courtesy of Bosch Rexroth AG.) (b) Functional scheme of the cushioning element. Hydraulic and pneumatic control lecture notes by Siraj K.

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The oil returned from the piston chamber (5) is forced to flow through the passage (6) to the throttle valve (7), and through the radial clearance between the spear and cylindrical cave. The pressure in the piston chamber increases and acts to decelerate the moving piston. The check valve (3) permits by-pass of the throttle valve at the start of the motion in the opposite direction. When extending the cylinder, the oil flows to the piston chamber through the check valve. In this way, the whole piston area is acted on by the pressurized oil.

The piston may be equipped with a cushioning element at one side or at both sides. The throttle valve is either of fixed or of adjustable area. The illustrated construction has a throttle valve area adjustable by a screw (see Fig. 3.2.26a). The kinetic energy of the moving parts should not exceed the capacity of the cushioning element, defined as the work done during cushioning period. The cushioning should produce a controlled deceleration of the cylinder, near one or both end positions. This is done by creating a decelerating pressure force. In doing this, the pressure must not exceed its limiting value. The kinetic energy of the moving parts is converted into heat by throttling the out-going fluid in the cushioning zone. For an ideal operation, the piston will be fully stopped at the end of the cushioning stroke, s. If the piston will be fully stopped at the end of the cushioning stroke, the required deceleration, a, is a

=

v2 s

When the cylinder is installed horizontally, the decelerating (cushioning) force can be calculated, considering the equilibrium of forces acting on the piston (see Fig. 3.2.26b), as follows: p d Ad

=

ma + pA p

Normally, the damping pressure may not exceed the nominal pressure of the cylinder. An average value of the damping pressure, Pd , is given as follows: p d

=

1  mv 2

 Ad  2s

+ pA p

  

Where a = Deceleration, m/s 2 2

Ad

=

Piston area subjected to pressure pd , m

A p

=

Piston area subjected to pressure p, m

2


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m = Moving mass, kg p

= Driving

p d

=

pressure, Pa

Mean pressure in the cushioning volume, Pa

s = Damping length, m v = Piston velocity at the beginning of the cushioning stroke, m/s

For vertical mounting of the cylinder, the pressure generated by the weight of the moving parts must be added or subtracted depending on the direction of motion. The cylinder friction is ignored in these calculations. If the calculations give an unacceptably high mean damping pressure, the damping length must be increased or the speed must be reduced.

Hydraulic shock absorber External hydraulic energy absorbing devices also are employed many times to reduce shock loading of machinery that would result in failure. Carriage stops on turntables, doors, transfer machines, turnover s, and small crane s requiring controlled deceleration use the se devices (Fig. 3.2.27). In operation, fluid is metered through adjustable orifice s for a wide range of impact load s and velocities. In Fig. 3.2.28, for example, liquid is metered through the orifice plate valve along the tapered metering pin as the piston is forced into the cylinder. Adjustment is accomplished by removing the protective plug and rotating the adjustment screw with a hexagonal socket key for more or less damping. The hardened and chrome plated tubular piston resists buckling and side load s under impact. The metered liquid is stored in the spring-loaded separator chamber which also repositions the piston.


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Figure 3.2.27. Typical deceleration application using shock absorbers.


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Figure 3.2.28. Typical hydraulic shock absorber with full-range adjustability (courtesy of Enidine Corporation).


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3.2 Hydraulic Cylinder

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