44721370-Hydraulics.pdf

7/31/2019 44721370-Hydraulics.pdf

1/149

Hydraulics

7/31/2019 44721370-Hydraulics.pdf

2/149

[1] Lathe

Machine-tool construction is a typical area of application of hydraulics.

With modern CNCmachine tools, the tools and workpieces are cla mped by hydraulic means. Feed motions

and the spindle drive can also be hydraulically po wered.

7/31/2019 44721370-Hydraulics.pdf

3/149

[2] P ress with elevated reservoir This is an application in which

extre mely high forces are required. Due to the suspended cylinder and the tractive load, special measures are required for the activation of the advance stroke. This in turn requires specially-designed press drives.

A special feature is the elevated reservoir, which utilizes the static pressure in the pressure mediu m.

7/31/2019 44721370-Hydraulics.pdf

4/149

[3] Mobile hydraulics: Excavator

On this hydraulic excavator, not only all working move ments

(linear drives) but also the propulsion of the vehicle (rotary drive) are hydraulically po wered. The primary drive of the excavator is an internal-co mb ustion engine.

7/31/2019 44721370-Hydraulics.pdf

5/149

[4.1] S tructure of a hydraulic

syste m This sim plified block diagra m sho ws the division of hydraulic

syste ms into a signal control section and a hydraulic po wer section. This signal control section is used to activate the valves in the po wer control section.

7/31/2019 44721370-Hydraulics.pdf

6/149

[4.2] Hydraulic po wer section The diagra m of the hydraulic

po wer section is co mple mented in this case by a circuit diagra m to allo w correlation of the various function groups; the po wer supply section contains the hydraulic

pu mp and drive motor and the co mponents for the preparation of the hydraulic fluid. The energy control section consists of the various valves used to provide control and regulate the flow rate, pressure and direction of the hydraulic fluid. This drive section consists of cylinders or hydraulic motors, depending on the application in question.

7/31/2019 44721370-Hydraulics.pdf

7/149

7/31/2019 44721370-Hydraulics.pdf

8/149

[5.1a ] Interaction of co mponents

( Animation)

7/31/2019 44721370-Hydraulics.pdf

9/149


( Animation)

7/31/2019 44721370-Hydraulics.pdf

10/149


( Animation)

7/31/2019 44721370-Hydraulics.pdf

11/149


( Animation)

7/31/2019 44721370-Hydraulics.pdf

12/149


( Animation)

7/31/2019 44721370-Hydraulics.pdf

13/149


( Animation)

7/31/2019 44721370-Hydraulics.pdf

14/149


( Animation)

7/31/2019 44721370-Hydraulics.pdf

15/149


( Animation)

7/31/2019 44721370-Hydraulics.pdf

16/149

[7] Circuit sy mb ols for energy

transfer (1) The sy mb ols sho wn are used in circuit diagra ms for energy transfer and hydraulic-fluid preparation.

In the interests of clarity, the lines in the circuit diagra m should be dra wn without cross-overs as far as possi ble.

7/31/2019 44721370-Hydraulics.pdf

17/149

[8] Circuit sy mb ols for energy

transfer (2) The direction of the arro ws in the circuit sy mb ols for the heater and cooler correspond to the direction of heat flow.

7/31/2019 44721370-Hydraulics.pdf

18/149

[9] C ircuit sy mb ols for energy

conversion Hydraulic pu mps are sho wn by a circle with a part representation of a drive shaft. Triangles in the circles sho wthe direction of flow. The triangles are sho wn solid, since pressure fluid is used in hydraulics.

If the pressure mediu m is gaseous, as in the case of pneu matics, the triangles are sho wn in outline.

7/31/2019 44721370-Hydraulics.pdf

19/149

[10] C ircuit sy mb ols for

hydraulic motors The sy mb ols for hydraulic motors are distinguished from the

sy mb ols for hydraulic pu m ps by the fact that the arro ws sho wing the direction of floware the other way round.

7/31/2019 44721370-Hydraulics.pdf

20/149

[11] C ircuit sy mb ols for single

acting cylindersS ingle acting cylinders have one port, i.e. pressure fluid can be applied only to the piston side. With these cylinders, the return stroke is produced either by external force, sho wn in the sy mb ol by an

opening bearing cap, or by a spring is sho wn within the sy mb ol in this latter case.

7/31/2019 44721370-Hydraulics.pdf

21/149

[12] C ircuit sy mb ols for dou ble

acting cylindersDou ble acting cylinders have two ports to allo w pressure fluid to be applied to both cylinder cha mb ers. The sy mb ol for a differential cylinder is distinguished fromthe sy mb ol for a dou ble acting cylinder by the two lines added to the end of the piston rod. The area ratio is generally 2:1. In the case of cylinders with

dou ble- ended piston rods, the sy mb ol sho ws that the piston areas are of equal size (synchronous cylinders).

7/31/2019 44721370-Hydraulics.pdf

22/149


directional control valves (1)Designations for directional control valves always give firstly the nu mb er of ports and then the nu mb er of s witching positions. Directional control valves always have at least two ports and at

least two s witching positions. The nu mb er of squares sho ws the nu mb er of possi ble s witching positions of a valve. Arrows within the squares sho w the direction of flow. Lines sho wn ho w the ports are interconnected in the various s witching positions of the valve. The designations always relate to the nor mal position of the valve.

7/31/2019 44721370-Hydraulics.pdf

23/149


directional control valves (2) This illustration sho ws the circuit sy mb ols for 4/2 -and 5/2 -way valves.

There are two general methods for the designation of ports, using either the letters P , T, R, A, B and L or consecutively using A, B, C, D etc.; the first method is the preferred one in the relevant standard.

7/31/2019 44721370-Hydraulics.pdf

24/149


directional control valves (3) The illustration sho ws the circuit sy mb ols for 4/3 -way valves with

various mid-positions.

7/31/2019 44721370-Hydraulics.pdf

25/149

[16] Circuit sy mb ols for manual

operation The s witching position of a directional control valve can be changed by various actuation methods. The sy mb ol for the valve is accordingly supple mented by a sy mb ol indicating the actuation methods sho wn, such as push buttons and pedals, a spring is always necessary for resetting. Resetting can,

ho wever, also be achieved by actuating the valve a second time, for exa mple in the case of valves with hand levers and detents.

7/31/2019 44721370-Hydraulics.pdf

26/149

[17] Circuit sy mb ols for

mechanical actuation This illustration sho ws the sy mb ols for ste mor push button, spring

and roller ste m.

7/31/2019 44721370-Hydraulics.pdf

27/149

[18] Circuit sy mb ol for pressure

valvesP ressure valves are represented using squares. The flow direction is indicated by an arro w. The valve ports can be designated as P(supply port) and T (tank return port) or as A and B. The position of the arro w within the square indicates whether the valve is nor mally open or nor mally closed. Adjusta ble pressure valves are indicated by a diagonal arro w through the spring. P ressure valves are divided into pressure relief valves and pressure regulators.

7/31/2019 44721370-Hydraulics.pdf

28/149

[19] C ircuit sy mb ols for flow

control valves A distinction is made in flowcontrol valves bet ween types which are affected by viscosity and those which are unaffected. Flow control valves unaffected by viscosity are ter med orifices. A 2-

way flow control valve consists of restrictors, one adjusta ble restrictor which is unaffected by viscosity (orifice) and a regulating restrictor (pressure co mpensator). These valves are represented by a rectangle containing the sy mb ol for the adjusta ble restrictor and an arro w to represent the pressure co mpensator. The diagonal arro wthrough the rectangle indicates that the valve is adjusta ble.

7/31/2019 44721370-Hydraulics.pdf

29/149

[20] C ircuit sy mb ols for non-

return valves The sy mb ol for non-return valves is a ball which is pressed against a seat. Delocka ble non-return valves are sho wn by a square containing the sy mb ol for a non- return valve. The pilot control for unlocking the non- return valve is indicated by a

broken line at the pilot port. The pilot port is designated by the letter X.

7/31/2019 44721370-Hydraulics.pdf

30/149


measuring devices The illustration sho ws the sy mb ols for measuring devices

used in hydraulics.

7/31/2019 44721370-Hydraulics.pdf

31/149

[22] Hydrostatic pressure Hydrostatic pressure is the

pressure created a bove a certain level within a liquid as a result of the weight of the liquid mass. Hydrostatic pressure is not dependent on the shape of the vessel concerned but only on the height and density of the colu mn of liquid.

Hydrostatic pressure can generally be ignored for the purpose of studying hydraulics

7/31/2019 44721370-Hydraulics.pdf

32/149

[23] P ressure propagationIf a force F acts on an area A of an enclosed liquid, a pressure p is produced which acts throughout the liquid (P ascal's La w).

Hydrostatic pressure has been ignored here. The ter m pressure propagation is also used to mean the pulse velocity in liquids (approx. 1000 m/ s).

7/31/2019 44721370-Hydraulics.pdf

33/149

[24] P ower trans missionIf a force F_1 is applied to an area A _1 of a liquid, a pressure p results. If, as in this case, the pressure acts on a larger surface A _2 , then a larger counter-force F_2 m ust be maintained. If A _2 is three times as large as A1, then F_2will also be three times as large as F_1 .

Hydraulic po wer trans mission is co mpara ble to the mechanical law of levers.

7/31/2019 44721370-Hydraulics.pdf

34/149

[25 .1] D isplace ment

trans mission (1)If the input piston of the hydraulic press travels a distance s _1 , a volu me of fluid will be displaced. This sa me volu me displaces the output piston by the distance s _2 . If the area of this piston is larger than that of the input piston, the distance s _2 w ill be shorter than s _1 .

Hydraulic displace ment trans mission is co mpara ble to the mechanical law of levers.

7/31/2019 44721370-Hydraulics.pdf

35/149

[25 .2] D isplace ment

trans mission (2)

7/31/2019 44721370-Hydraulics.pdf

36/149

[26. 1] P ressure transfer (1) The fluid pressure p _1 exerts a

force F_1 on the surface A _1which is transferred via the piston rod to the s mall piston. The force F_1 thus acts on the surface A _2and produces the fluid pressure

p2 . S ince the piston area A _2 is s maller than the piston area A _1 , the pressure p _2 m ust be larger than the pressure p _1 .

The pressure-transfer (pressure-intensification) effect is put to practical use in pneu matic /hydraulic pressure intensifiers and also in purely hydraulic syste ms when extre mely high pressures are required which a pu mp cannot deliver.

7/31/2019 44721370-Hydraulics.pdf

37/149

[26. 2] P ressure transfer (2) A pressure-transfer effect

also occurs in conventional dou ble acting cylinders with single piston rod.

This effect also causes pro blems in hydraulics. If, for exa mple, an exhaust flow control is fitted to a differential cylinder for the

advance stroke, a pressure- intensification effect results in the piston-rod cha mb er.

7/31/2019 44721370-Hydraulics.pdf

38/149

[27] Types of flow A distinction is made bet ween

laminar flow and tur bulent flow. In the case of laminar flow, the hydraulic fluid moves through the pipe in ordered cylindrical

layers. If the flow velocity of the hydraulic fluid rises a bove a critical speed, the fluid particles at the center of the pipe break a way to the side, and tur bulence results.

Tur bulent flow should be avoided in hydraulic circuits by ensuring they are adequate sized.

7/31/2019 44721370-Hydraulics.pdf

39/149

[28a ] Diesel effect ( Animation)

A pressure drop to the level of vacuu m m ay occur at points of restriction, causing precipitation of the air dissolved in the oil. When the pressure rises again, oil bursts into the gas

bubb les and spontaneous ignition of the oil/air mixture may occur.

7/31/2019 44721370-Hydraulics.pdf

40/149

[29] C avitation Motion energy is required for

an increase in the flow velocity of the oil at a restriction. This motion energy is derived fromthe pressure energy. If the vacuu m w hich results is s maller than -0.3 b ar, air dissolved in the oil is precipitated out. When the pressure rises again due to a reduction in speed, the oil bursts into the gas bubb les.

Cavitation is a significant factor in hydraulic syste ms as a cause of wear in devices and connections.

7/31/2019 44721370-Hydraulics.pdf

41/149

[29 a ] Cavitation ( Animation)

Local pressure peaks occur during cavitation. This causes the erosion of s mall particles from the wall of the pipe imm ediately after the reduced cross-section, leading to material fatigue

and often also to fractures. This effect is acco mpanied by considera ble noise.

7/31/2019 44721370-Hydraulics.pdf

42/149

[30] Input and output po wer Various losses occur at

the individual devices within a hydraulic control chain. These consist essentially of mechanical, electrical and volu metric losses.

After an installation has been in service for so me time, there will be a

change in particular in the volu metric efficiency of the pu mp, as the result, for exa mple, of cavitation

7/31/2019 44721370-Hydraulics.pdf

43/149

[31 .1] Hydraulic po wer unit The hydraulic po wer unit

(po wer supply unit) provides the energy required for the hydraulic installation. Its most important co mponents are the

reservoir (tank) , drive (electric motor), hydraulic pu mp, pressure relief valve (safety valve), filter and cooler. The hydraulic po wer unit may also act as a carrier for other

devices (gauges, directional control valves).

7/31/2019 44721370-Hydraulics.pdf

44/149

[31 .2] Hydraulic po wer unit:

Reservoir The hydraulic reservoir contains the hydraulic fluid required the operate the installation. Within the reservoir, air, water and solid matter are separated out of the hydraulic fluid.

The size of the reservoir will depend on the practical application involved; for stationary syste ms, the volu me of fluid delivered by the pu mp in 3 to 5minutes can be taken as a guide. In mobile hydraulic syste ms, on the other hand, the reservoir contains only the maxi mumquantity of hydraulic fluid required.

7/31/2019 44721370-Hydraulics.pdf

45/149

[32] E xternally toothed gear

pu mp The increase in volu me which results when a tooth moves out of mesh produces a vacuu m in the suction area. The hydraulic fluid is conveyed into the pressure area. The hydraulic fluid is then forced out of the tooth gaps by the meshing of the teeth and displaced into the a bove supply line.

7/31/2019 44721370-Hydraulics.pdf

46/149

[33] Internally toothed gear

pu mp The inner gear is driven by a motor. The teeth of the inner wheel drive the outer gear wheel. The rotary motion creates a vacuu m in the gaps bet ween the teeth, causing hydraulic fluid to be sucked in. On the other side, the teeth engage once more and oil is displaced from the tooth cha mb ers.

The design can deliver

pressures of up to approx. 175bar. Hydraulic motors represent the reverse of the function principle.

7/31/2019 44721370-Hydraulics.pdf

47/149

[34] C ircuit diagra m: Return flow

filter An oil filter situated in the return line to the tank has the advantage that the filter is thus easy to

maintain. A disadvantage, ho wever, is that conta mination is re moved from the hydraulic fluid only after it has passed

through the hydraulic co mponents. This configuration is often

used.

7/31/2019 44721370-Hydraulics.pdf

48/149

[35] C ircuit diagra m : P ump inlet filter

With this configuration, the pu mp is protected from conta mination. The filter is, on the other

hand, less easily accessi ble.If these filters have a too fine mesh, suction pro blems and cavitation

effects may occur. Additional coarse filters upstrea m of the pu mp are reco mm ended.

7/31/2019 44721370-Hydraulics.pdf

49/149

[36] Circuit diagra m: P ressure line filter

P ressure filters can be installed selectively upstrea m of valves which are sensitive to

conta mination; this also ena bles s maller mesh sizes to be used.

A pressure-resistant housing is required,

which makes this configuration more expensive.

7/31/2019 44721370-Hydraulics.pdf

50/149

[37] Circuit diagra m: Conta mination indicator

It is important that the effectiveness of a filter can be checked by a conta mination indicator. The conta mination of a filter is measured by the pressure drop; as the conta mination increases, the pressure upstrea mof the filter increases. The pressure acts on a spring- loaded piston. As the pressure increases, the piston is pushed against a spring.

There are a nu mb er of different display methods. Either the piston move ment is directly visible or it is converted into an electrical or visual indication by electrical contacts.

7/31/2019 44721370-Hydraulics.pdf

51/149

[38] Water cooler With this design of cooler, hydraulic fluid is fed through tubes over which coolant (water) flows. The heat which is discharged can be re-used.

The operating te mperature in

hydraulic installations should not exceed 50 - 60C , since this would cause an unaccepta ble reduction in viscosity, leading to pre mature aging of the fluid. In co mparison with air cooling, operating costs a higher due to the required coolant and the suscepti bility to corrosion. Te mperature difference of up to approx. 35C can be handled.

7/31/2019 44721370-Hydraulics.pdf

52/149

[39] Air cooler

Hydraulic fluid fromthe return line flows through a coiled pipe which is cooled by a fan.

The advantages here are simplicity of installation and lowoperating costs. The noise of the fan may be a nuisance

7/31/2019 44721370-Hydraulics.pdf

53/149

[40] Heating ele ment Heaters are often

required to ensure that the opti mum operating te mperature is reached

quickly. Heating ele ments or flow preheaters are used for heating and pre-heating hydraulic fluid.If the viscosity is to high,

the resulting increase in friction and cavitation leads to greater wear.

7/31/2019 44721370-Hydraulics.pdf

54/149

[41] C ircuit diagra m: Hydraulic po wer unit

The illustration sho ws the detailed circuit sy mb ol for a hydraulic

po wer unit.S ince this is an co mb ination unit, a dot /dash line is placed around the sy mb ols representing the individual units.

7/31/2019 44721370-Hydraulics.pdf

55/149

[42] Actuating force

With so me types of poppet valves, the actuating force, which is dependent on pressure and area, may be very high. In order to avoid this, pressure co mpensation may be provided at the valves.

7/31/2019 44721370-Hydraulics.pdf

56/149

[43] P oppet principle Valves are based either

on the poppet principle or slide principle. In poppet valves, a ball, a cone or a disc is pressed by a spring against the seat of a passage. The high pressure per unit area which is created, means that valves of this kind provide a very efficient seal. The illustration sho ws a cone used as a sealing ele ment.

7/31/2019 44721370-Hydraulics.pdf

57/149

[44] S lide principle This illustration sho ws the

principle of a longitudinal slide valve. In order to allo w the piston to move, it has a certain clearance and floats in

hydraulic fluids. Ring grooves ensure an even film of oil and thus pressure equili brium. The piston can thus be moved with minimal frictional losses.

This type of valve cannot

provide a perfect seal, which means that there is always a certain oil leakage.

7/31/2019 44721370-Hydraulics.pdf

58/149

[45] P oppet valves

In poppet valves, a ball, cone or occasionally a disk is

pressed against a seat area to act as a sealing ele ment. Valves of this type

provide a very efficient seal.

7/31/2019 44721370-Hydraulics.pdf

59/149

[46] P iston overlap The s witching characteristics of a

valve are governed by, a mong other things, its piston overlap. A distinction is made bet ween positive, negative and zero overlap. In the case of positive overlap, the port in question is co mpletely covered by the piston, while with negative overlap it is less than co mpletely covered. In the case of zero overlap, the distances bet ween the control edges of the piston and of the port are exactly the sa me.

The individual control edges of the pilot piston can have different overlaps.

7/31/2019 44721370-Hydraulics.pdf

60/149

7/31/2019 44721370-Hydraulics.pdf

61/149

[47. 2] P ositive s witching overlap

In the case of positive overlap, the left-hand piston does not open the passage from P to A until the tank has been co mpletely isolated by the other piston. P ressure is imm ediately fed to the

load device (cylinder or hydraulic motor) with the result that this starts a bruptly.

7/31/2019 44721370-Hydraulics.pdf

62/149

[50 .1] P ressure relief valve (1)In this design incorporating a poppet valve, a seal is pressed against the inlet port P b y

a pressure spring when the valve is in its nor mal position.In this situation, for exa mple, an unloaded

piston rod is executing an advance stroke and the entire pu mp delivery is flowing to the cylinder.

7/31/2019 44721370-Hydraulics.pdf

63/149

[50 .2] C ircuit diagra m: P ressure relief valve (2)

As soon as the force exerted by the inlet pressure at A exceeds the opposing spring force, the valve begins to open.In this situation, for exa mple, the piston rod is fully advanced; the entire

pu mp delivery is flowing at the preset syste mpressure to the tank.

7/31/2019 44721370-Hydraulics.pdf

64/149

[51 .1] PR V used to limit syste mpressure

This illustration sho ws a pressure relief valve within a basic hydraulic circuit (used to control a

dou ble acting cylinder). The resistances at the outlet (tank line, filter) must be added to the force of the spring in the

pressure relief valve. S ee also the ani mation Interaction of co mponents (topic 5).

7/31/2019 44721370-Hydraulics.pdf

65/149

[51 .2] PR V used to limit syste mpressure

This illustration sho ws the sa me circuit as the previous

illustration, but with the cut-a way vie w of the PR V replaced by the appropriate circuit

sy mb ol.

7/31/2019 44721370-Hydraulics.pdf

66/149

[52 a ] Circuit without brake valve ( Animation)

One application of pressure relief valves is as brake valves; these prevent pressure peaks which may other wise occur as the result of mass moments of

inertia when a directional control valve is suddenly closed. The ani mation sho ws an (incorrect) circuit in sche matic for m in which the working line on the exhaust

side has fractured due to the a bsence of a brake valve. The next ani mation sho ws the

correct circuit.

7/31/2019 44721370-Hydraulics.pdf

67/149

[52 .1a ] Circuit without brake valve ( Animation)

7/31/2019 44721370-Hydraulics.pdf

68/149


7/31/2019 44721370-Hydraulics.pdf

69/149


7/31/2019 44721370-Hydraulics.pdf

70/149


7/31/2019 44721370-Hydraulics.pdf

71/149

[53] C ircuit diagra m: Brake valve

This illustration sho ws the correct circuit for the pro blemin topic 52 . This circuit incorporates not only a brake valve on the piston-rod side

but also a non-return valve on the inlet side via which oil can be taken in from a reservoir during the vacuu m phase following the closure of the directional control valve.

The following ani mation sho ws the events which occur in the two working lines.

7/31/2019 44721370-Hydraulics.pdf

72/149

[53 a ] Circuit with brake valve ( Animation)

The ani mation 53 .1a sho ws in sche matic for mthe behavior of the PR V during the braking phase, while 53 .2a sho ws the behavior of the non-return valve (NR V) in the supply line and 53 a sho ws the two events together in su mm ary.

The necessity of the brake valve can be de monstrated by the preceding ani mation.

[ ] h b k l

7/31/2019 44721370-Hydraulics.pdf

73/149

[53 .1a ] Circuit with brake valve ( Animation)

7/31/2019 44721370-Hydraulics.pdf

74/149

[54] C i i di PR V

7/31/2019 44721370-Hydraulics.pdf

75/149

[54] C ircuit diagra m: PR V as back-pressure valve

Back-pressure valves counteract mass moments of inertia with tractive loads. The illustration sho ws a circuit with a back-pressure valve on the

piston-rod side. On the return stroke, the PR V is by-passed by an NR V.

The PR V must be pressure-co mpensated and the tank port must be capa ble of carrying a

pressure load.

[55] PR V i ll ll d

7/31/2019 44721370-Hydraulics.pdf

76/149

[55] PR V, internally controlled, cushioned

P ressure relief valves often incorporate cushioning pistons or flow control valves. The cushioning device sho wn provides fast opening and slo wclosing of the valve. This prevents da mage caused by pressure shocks (s mooth valve operation).P ressure shock arise, for exa mple, when the pu mp delivers oil in an almost unpressurized condition and the supply port of the load device is a bruptly closed by a directional control valve.

[56 1] PR V ll ll d

7/31/2019 44721370-Hydraulics.pdf

77/149

[56. 1] PR V, externally controlled (1)

This pressure relief valve controls the flow in accordance with an external pressure setting. This pressure acts against an adjusta ble spring force. The passage from the supply port P to the tank port T re mains closed as long as no load acts on the pilot piston.

[56 2] PR V ll ll d

7/31/2019 44721370-Hydraulics.pdf

78/149

[56. 2] PR V, externally controlled (2)

P ressure can be fed to the pilot piston via the pilot port X. As

soon as the pressure force at the pilot piston exceeds the preset spring force,

the pilot piston is displaced, allo wing free flow.

7/31/2019 44721370-Hydraulics.pdf

79/149

[57. 1] S equence valve The exa mple sho ws a circuit

with a pressure relief valve used as a pressure sequence valve. The pressure at the pilot piston of the PR V rises via the

pressure regulator. The PR V opens and the high-pressure pu mp delivers directly to the tank. As soon as the 2/2 -way valve opens, the pressure drops. The pressure relief valve closes and the high pressure pu mp is connected to the syste m.

[57 2] C i i di

7/31/2019 44721370-Hydraulics.pdf

80/149

[57. 2] C ircuit diagra m: S equence valve

This illustration sho ws the sa me circuit as the previous

illustration, but with the cut-a way vie w of the sequence valve replaced by the

appropriate circuit sy mb ol.

7/31/2019 44721370-Hydraulics.pdf

81/149

[58] P ressure relief valve

Actual photograph of a PR V (Fa. Hydronor ma).

[59 1] 2 l t

7/31/2019 44721370-Hydraulics.pdf

82/149

[59 .1] 2 -way pressure regulator (1 )

This valve is nor mally open. The outlet pressure ( A) acts via a pilot line on the left-hand surface of the pilot piston against an adjusta ble spring force.P ressure regulators reduce the inlet pressure to an adjusta ble outlet pressure. It is appropriate to use these in hydraulic installations only if different pressures are required.

[59 2] 2 g l t

7/31/2019 44721370-Hydraulics.pdf

83/149


When the pressure rises at outlet A, the force at the left-hand surface of the pilot piston beco mes greater, the piston is displaced to the right and the

throttle gap beco mes narro wer. This causes a pressure drop.In the case of slide valves, it is also possi ble to design the control edges in such way that the opening gap increases

only slo wly. This gives greater control precision.

[59 3] 2 g l t

7/31/2019 44721370-Hydraulics.pdf

84/149


When the preset maximum pressure is reached, the throttle

point closes co mpletely; the pressure set on the pressure relief valve

is produced at the inlet P .

[59 4] 2 g l t

7/31/2019 44721370-Hydraulics.pdf

85/149


In the circuit illustrated, the piston rod of the cylinder is

executing an advance stroke. The pressure at the outlet A of the pressure regulator is

less than the syste mpressure at P and constant.

[59 5] 2 a press re reg lator

7/31/2019 44721370-Hydraulics.pdf

86/149


The piston rod of the cylinder is no w in its for ward end position.

The pressure at outlet A thus continues to rise and the throttle point closes

co mpletely.

[60] C ircuit diagra m: 2 way

7/31/2019 44721370-Hydraulics.pdf

87/149

[60] C ircuit diagra m: 2-way pressure regulator

The illustration sho ws the sa me circuit as the previous

illustration, but with the 2-way pressure regulator in the for mof a circuit sy mb ol.

[61] C ircuit diagra m: 2 way

7/31/2019 44721370-Hydraulics.pdf

88/149

[61] C ircuit diagra m: 2-way pressure regulator

It is appropriate to use PR Vs only when different pressures are required in an installation. The mod of operation of pressure regulator will thus be explained here by taking an exa mple with two control circuits. The first control circuit acts via a flow control valve on a hydraulic motor which drives a roller. This roller is used to stick together multi-layered printed circuit boards. The second control circuit acts on a hydraulic cylinder which dra ws the roller towards the boards at an adjusta ble reduced pressure.

This exa mple can be used as a preli minary stage to the introduction of the 3-way PR . If the 2-way PR is closed due to the fact that the preset maxi mum pressure has been reached, thickening of the material of the workpieces would cause an increase in the pressure on the outlet side of the PR to a higher value than desired.

7/31/2019 44721370-Hydraulics.pdf

89/149

[64.1] 2/2 -way valve (1) The 2/2 -way valve has a working port A, a supply port P and a leakage-oil port L. In the case of the valve sho wn here, of slide design, flow from P to A is closed in the nor mal position.

A relief line leading to the leakage-oil port is provided to prevent a build-up of pressure in the spring and piston cha mb ers.

7/31/2019 44721370-Hydraulics.pdf

90/149

[64.2] 2/2 -way valve (2)

The 2/2 -way valve is actuated and the passage from P to A

is open.

2/2 -way valves are also availa ble which are nor mally open from P to A.

[65 1] 2/2 way valve as by pass

7/31/2019 44721370-Hydraulics.pdf

91/149

[65.1] 2/2 -way valve as by-pass valve

This exa mple sho ws a 2/2 -way valve used as a by-pass valve;

when the 2/2 -way valve is actuated, the flow control valve 0V3is by-passed, causing

the piston rod of the cylinder to advance at maximum speed.

[65 2] C ircuit diagra m: 2/2 way

7/31/2019 44721370-Hydraulics.pdf

92/149

[65.2] C ircuit diagra m: 2/2 -way valve as by-pass valve


illustration, but with the functional representation of the 2/2 -way valve

replaced by a circuit sy mb ol.

[66 ] Circuit diagra m: 2/2 way

7/31/2019 44721370-Hydraulics.pdf

93/149

[66 ] Circuit diagra m: 2/2 -way valve as final control ele ment

In its initial position, the cylinder is advanced. If the 2/2 -way valve 0V1 is actuated, the entire volu metric flow passes to the tank and piston rod of the cylinder is reset by the

external load m. If 0V1 is not actuated, the syste m pressure set on the pressure limiter 0V2builds up and the piston rod advances.In the initial position, the pu mp operates against the preset syste m pressure, which has an unfavora ble effect on the po wer balance of the circuit sho wn.

[66a ] 2/2 way valve as final

7/31/2019 44721370-Hydraulics.pdf

94/149

[66a ] 2/2 -way valve as final control ele ment ( Animation)

The ani mations sho wthe actuation and release of the 2/2 -way

valve, which causes the piston rod of the cylinder to advance and retract.

[66 1a ] 2/2 way valve as final

7/31/2019 44721370-Hydraulics.pdf

95/149

[66. 1a ] 2/2 -way valve as final control ele ment ( Animation)

[66 2a ] 2/2 way valve as final

7/31/2019 44721370-Hydraulics.pdf

96/149

[66. 2a ] 2/2 -way valve as final control ele ment ( Animation)

[69 1] 3/2 -way valve poppet

7/31/2019 44721370-Hydraulics.pdf

97/149

[69.1] 3/2 -way valve, poppet principle (1)

The 3/2 -way valve has working port A, a supply port P and a tank port T. Volu metric flow can be routed from the supply port to the working port or from the working port to the tank port. The third port in each case is closed. In the nor mal position sho wn, P is closed and flow released from A to T.

[69 2] 3/2 -way valve poppet

7/31/2019 44721370-Hydraulics.pdf

98/149

[69.2] 3/2 -way valve, poppet principle (2)

The 3/2 -way valve is actuated; flow is released from P to A,

the outlet T is closed.3/2 -way valves which are nor mally open from P to A and T

closed are also availa ble.

7/31/2019 44721370-Hydraulics.pdf

99/149

[70a ] 3/2 -way valve ( Animation)

The ani mations sho wthe actuation and release of the m anual

push button for a 3/2 -way valve, which causes the piston rod of the cylinder to

advance and retract.

[70 1] 3/2 -way valve as final

7/31/2019 44721370-Hydraulics.pdf

100/149

[70.1] 3/2 -way valve as final control ele ment

The circuit sho ws the 3/2 -way valve in a functional representation as a final control ele ment of a

single acting cylinder. The non-return valve protects the pu mp in cases where the 3/2 -way

valve is actuated and the piston rod is su b ject to an external load.

[70 1a ] 3/2 -way valve

7/31/2019 44721370-Hydraulics.pdf

101/149

[70.1a ] 3/2 way valve ( Animation)

[70 2] C ircuit diagra m: 3/2 -way

7/31/2019 44721370-Hydraulics.pdf

102/149

[70.2] C ircuit diagra m: 3/2 way valve as final control ele ment


illustration, but with the circuit sy mb ol for the 3/2 -way valve.

[70 2a ] 3/2 -way valve

7/31/2019 44721370-Hydraulics.pdf

103/149

[70.2a ] 3/2 way valve ( Animation)

[71 1] 3/2 -way valve slide

7/31/2019 44721370-Hydraulics.pdf

104/149

[71.1] 3/2 way valve, slide principle (1)

The 3/2 -way valve has a working port A, a supply port P and a tank port T. The volu metric flow can be routed from the supply port to the working port, or from the working port to the tank port. The third port in each case is closed. In the nor mal position sho wn, P is closed and flow is released from A to T.

[71 2] 3/2 -way valve slide

7/31/2019 44721370-Hydraulics.pdf

105/149

[71.2] 3/2 way valve, slide principle (2)

The 3/2 -way valve is actuated; flow is released from P to A,

and the outlet T is closed.3/2 -way valves which are nor mally closed

from P to A and T are also availa ble.

7/31/2019 44721370-Hydraulics.pdf

106/149

[72] 3/2 -way valves as diverter In addition to their application as final control ele ments, 3/2 -way valves can also be used as diverters. In this case, port T is connected to a further device, to which a s witch-over

can then be made. The part circuit diagra ms sho w the facility to s witch bet ween the flow control valves with different settings and bet ween heating and cooling.

The circuit sy mb ol is dra wn reversed to simplify the representation of the circuit diagra m.

7/31/2019 44721370-Hydraulics.pdf

107/149

[73.2] 4/2 -way valve, two

7/31/2019 44721370-Hydraulics.pdf

108/149

[73.2] 4/2 way valve, two pistons (2)

The 4/2 -way valve is actuated, and there is flow from P to A and

from B to T.4/2 -way valves are also availa ble which are nor mally open

from P to A and fromB to T.

[74.1] 4/2 -way valve, three

7/31/2019 44721370-Hydraulics.pdf

109/149

[74.1] 4/2 way valve, three pistons (1)

This 4/2 -way valve has two working ports A and B, a supply port P and a tank port T. The supply port is always connected to one of the working ports, while the second working port is routed to the tank. In the neutral position, there is flow from P to B and from A to T.4/2 -way valves with three pistons require a leakage-oil port, since hydraulic fluid would other wise be trapped within the valve.


7/31/2019 44721370-Hydraulics.pdf

110/149


The 4/2 -way valve is actuated, and there is flow from P to A and

from B to T.


7/31/2019 44721370-Hydraulics.pdf

111/149


The circuit sho ws the 4/2 -way valve in functional representation as a final control ele ment of a dou ble acting cylinder.

The non-return valve protects the pu mp in cases where the piston

rod of the cylinder is su b ject to an external load.

[75.2] C ircuit diagra m: 4/2 -way

7/31/2019 44721370-Hydraulics.pdf

112/149

[ 5. ] C cu t d ag a : / wayvalve


illustration, but with the 4/2 -way valve as a circuit sy mb ol.

[76. 1] 4/3 -way valve with pu mp

7/31/2019 44721370-Hydraulics.pdf

113/149

[ ] y p pbypass (1)

From the logic point of vie w, 4/3 -way valves are 4/2 - way valves with an additional mid-position. There are various versions of this mid-position (in the mid-position in the

exa mple sho wn, the supply port P is directly connected to the tank T, see next illustration). In the s witching position sho wn, there is flowfrom P to B and from A to T.

4/3 -way valves are easy to construct as slide valves and of co mplex design as poppet valves.


7/31/2019 44721370-Hydraulics.pdf

114/149

[ ] y p pbypass (2)

The 4/3 -way valve is in its mid-position; there is flow from P to T, while A and B are closed. S ince the output from the pu mp flows to the tank, this s witching position is called pu mp bypass or also pu mp recirculation.

In the case of pu mp bypass, the pu mp needs to operate

only against the resistance of the valve, which has a favora ble effect on the po wer balance.


7/31/2019 44721370-Hydraulics.pdf

115/149

[ ] y p pbypass (3)

The valve is in its left-hand s witching position; there is flow

from P to A and fromB to T.

7/31/2019 44721370-Hydraulics.pdf

116/149


7/31/2019 44721370-Hydraulics.pdf

117/149

[ ] y p pbypass (4)

The circuit sho ws the 4/3 -way valve in functional representation as a final control ele ment of a dou ble acting cylinder. The valve is in its mid-position; the pu mp delivery flows via the by-pass line within the pilot piston to the tank.

The non-return valve protects the pu mp in cases where the piston rod of the cylinder is su b ject to an external load.

7/31/2019 44721370-Hydraulics.pdf

118/149

[77. 2] C ircuit diagra m: 4/3 -way

7/31/2019 44721370-Hydraulics.pdf

119/149

[ ] g yvalve with pu mp bypass


illustration, but with the 4/3 -way valve as a circuit sy mb ol.

[77. 2a ] 4/3 -way valve with pu mp

7/31/2019 44721370-Hydraulics.pdf

120/149

y p pbypass ( Animation)


7/31/2019 44721370-Hydraulics.pdf

121/149



7/31/2019 44721370-Hydraulics.pdf

122/149



7/31/2019 44721370-Hydraulics.pdf

123/149


[78. 1] 4/3 -way valve with closed

7/31/2019 44721370-Hydraulics.pdf

124/149

mid-position (1)From the logic point of vie w, 4/3 -way valves are 4/2 - way valves with an additional mid-position. There are various

versions of this mid-position (in the mid-position in the exa mple sho wn, all ports are closed in the mid-position, see next illustration). In the s witching position sho wn, there is flow from P to Band from A to T.


7/31/2019 44721370-Hydraulics.pdf

125/149

mid-position (2) The 4/3 -way valve is in its mid-position; all ports apart from the leakage-oil port are closed.

In this mid-position, the pu mp is operating against the syste mpressure set on the pressure relief valve.


7/31/2019 44721370-Hydraulics.pdf

126/149

mid-position (3) The valve is in its left-hand s witching position; there is flowfrom P to A and fromB to T.

[79.1] 4/3 -way valve with closed

7/31/2019 44721370-Hydraulics.pdf

127/149

mid-position (4) The circuit sho ws the 4/3 -way

valve in functional representation as a final control ele ment of a dou ble acting cylinder. The valve is in its mid-position; the pu mp is operating against the syste mpressure set on the PR V.

If, with an operational installation, it is desired to s witch to pu mp recirculation, this can be achieved by using an additional 2/2 -way valve as a changeover valve (see part circuit-diagra m in topic 67).

[79.2] C ircuit diagra m: 4/3 -way

7/31/2019 44721370-Hydraulics.pdf

128/149

valve with closed mid-position The illustration sho ws the sa me circuit as the previous illustration, but with the 4/3 -way valve as a circuit sy mb ol.

[80.1] 4/3 -way valve: overlap

7/31/2019 44721370-Hydraulics.pdf

129/149

positions (1) The illustration sho ws the left-

hand overlap position of a 4/3 -way valve with positive overlap in the mid-position (closed mid-position). This overlap position is a mixture of positive and negative overlap; P is connected to A, B and T are closed.

With 4/3 -way valves, the types

of overlap positions is generally specified in the data sheet.

[80.2] 4/3 -way valve: overlap

7/31/2019 44721370-Hydraulics.pdf

130/149

positions (2) The illustration sho ws the right-hand overlap position of a 4/3 -way valve with positive

overlap in the mid-position (closed mid-position). This overlap position, too, is a mixture of positive and negative overlap; P is connected to B, A and T are closed.

[81] D irectional control valve

7/31/2019 44721370-Hydraulics.pdf

131/149

[81] D irectional control valve

Actual photograph of a directional control valve with lever actuation (Fa. Denison).

[82] 4/3 way module

7/31/2019 44721370-Hydraulics.pdf

132/149

[82] 4/3 -way module

This 4/3 -way module with hand-lever actuation is used in vertical interconnection syste ms (m odular hydraulics).

[83 1] N on-return valve (1)

7/31/2019 44721370-Hydraulics.pdf

133/149

[83.1] N on-return valve (1)Non-return valves block flow in one direction and allo w free flow in the other. In the direction of flow sho wn, the sealing ele ment is pressed against a seat by a spring and the hydraulic fluid.

These valves are also availa ble in designs without springs. S ince there must be

no leaks in the closed position, these valves are generally of poppet design.

[83 2] N on-return valve (2)

7/31/2019 44721370-Hydraulics.pdf

134/149

[83.2] N on-return valve (2)

In the direction of flowsho wn, the valve is opened by the hydraulic fluid, which lifts the sealing ele ment from the seat.

[84] C ircuit diagra m: P ump

7/31/2019 44721370-Hydraulics.pdf

135/149

protectionIn this circuit, the non-return valve is used to protect the pu mp. This prevents a load pressure

from driving the pu mp in reverse when the electric motor is s witched off. P ressure peaks do not affect the pu mp but are discharged via the pressure relief valve.

[97] S ingle acting cylinder

7/31/2019 44721370-Hydraulics.pdf

136/149

[97] S ingle acting cylinder In the case of a single acting cylinder, only the piston side is pressurized with hydraulic fluid. The cylinder can thus carry out work only in one direction. The fluid which flows into the piston cha mb er causes a pressure to build up the surface of the piston. The piston travels into its for ward end position. The return stroke is effected by a spring, the dead weight of the piston rod or an external load.

[98] P lunger cylinder

7/31/2019 44721370-Hydraulics.pdf

137/149

[98] P lunger cylinder

In the case of plunger cylinders, the piston and rod for m a single co mponent. Due to the

design of the cylinder, the return stroke can only be effected by external forces. The cylinders can therefore generally be installed only vertically.

[99] D ou ble acting cylinder

7/31/2019 44721370-Hydraulics.pdf

138/149

[99] D ou ble acting cylinder In the case of dou ble acting cylinders, both piston surfaces can be pressurized. A working move ment can thus be perfor med in both directions.

With dou ble acting cylinders with a single-sided piston rod, different forces and speeds are obtained on the advance and return strokes due to the difference in area bet ween the piston surface and annular piston surface.


7/31/2019 44721370-Hydraulics.pdf

139/149

with end position cushioningCylinder with end position cushioning are used to brake high stroke speeds s moothly and prevent hard impacts at the end

of the stroke. S hortly before the end position is reached, the cross-section for the outflo w of fluid is reduced by the built-in cushioning pistons

and then finally closed. The hydraulic fluid is then forced to escape through a flow control valve.

[101 a ] End position cushioning

7/31/2019 44721370-Hydraulics.pdf

140/149

( Animation) The illustration sho ws first the

advance of the piston rod froma mid-position to the for ward end position, with cushioning at the end of the advance move ment. The non-return valve is open during the return stroke.

Animation 101 .3a also sho ws the opening of the pressure limiter after a certain pressure has been built up on the outlet side by the cushioning piston.

[101 .1] E nd position cushioning

7/31/2019 44721370-Hydraulics.pdf

141/149

(1) The piston is a short distance

before its end position; the hydraulic fluid on the piston-rod side must escape via the adjusta ble flow control valve a bove the piston rod

This type of end position cushioning is used for stroke speed bet ween 6 m/m in and 20 m/m in. At higher speed, additional cushioning or braking devices must be used.

[101 .1a ] End position

7/31/2019 44721370-Hydraulics.pdf

142/149

cushioning ( Animation)

[101 .2] E nd position cushioning

7/31/2019 44721370-Hydraulics.pdf

143/149

(2) The piston rod is on its return stroke; in this flow direction, the non-return valve belo w the piston rod is opened, thus by-passing the flowcontrol valve. The piston rod retracts at maximum speed.

[101 .2a ] End position

7/31/2019 44721370-Hydraulics.pdf

144/149

cushioning ( Animation)


7/31/2019 44721370-Hydraulics.pdf

145/149


Actual photograph of a dou ble acting cylinder.

[103 a ] Auto matic bleed valve ( )

7/31/2019 44721370-Hydraulics.pdf

146/149

( Animation)When the cylinder is retracted, the piston of the bleed valve is closed. It is lifted as the piston rod advances. Air can then escape via the bleed hole until the hydraulic fluid reaches the piston and pushes it up wards. In the for ward end position, the piston is pushed fully up wards by the hydraulic fluid and thus provides an external seal.

Bleed valves should be fitted at the highest point in a piping syste m, since this is where any trapped air will collect.

[103 .1a ] Auto matic bleed valve (A i i )

7/31/2019 44721370-Hydraulics.pdf

147/149

( Animation)

[103 .2a ] Auto matic bleed valve(A i i )

7/31/2019 44721370-Hydraulics.pdf

148/149

( Animation)

[103 .3a ] Auto matic bleed valve (A i i )

7/31/2019 44721370-Hydraulics.pdf

149/149

( Animation)

44721370-Hydraulics.pdf

Documents