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Hydralics > hydraulic valves > Flashcards

hydraulic valves Flashcards

1
Q

characteristics of pressure reducing valves

A

pilot pressure to close the valve is sensed downstream . inlet port is connected to system pressure . outlet port is connected to the circuit to be operated at a reduced pressure . drain line is required to allow internal leakage to return to the reservoir

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2
Q

all relief valves have the following characteristics no matter where they are located in the system

A

a relief valve is always normally closed . pilot pressure to open the valve is connected in parallel directly upstream of the valve . inlet is connected in parallel with the system or circuit it protects . outlet port is connected to the reservoir

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3
Q

circuit relief valves

A

limit pressure in one branch of a system

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4
Q

three types of back pressure valves are

A

counterbalance valves . brake valves . lock valves

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5
Q

the amount of oil flow that passes through an orifice is determined by

A

size and shape . pressure drop across the orifice . the viscosity of the oil

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6
Q

two other advantages of pilot operated control valves

A

much less prone to chatter . can operate through a much wider pressure range than a direct acting valve

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7
Q

three common designs of normally closed direct acting pressure control valves

A

ball type . poppet type . guided poppet type

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8
Q

flow control valves control

A

the speed of hydraulic pumps and motors

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9
Q

guided poppet type normally closed direct acting pressure control valve

A

closely fitted into the body making it more stable than the other two designs

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10
Q

ball type normally closed direct acting pressure control valves

A

the simplest . cannot handle a large flow of oil without chattering severely

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11
Q

what is valve modulation

A

the constant movement from open to closed balancing spring force against hydraulic pressure determined by the changing oil flow

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12
Q

characteristics of a sequence valve

A

normally closed . pilot pressure to open valve is sensed up stream . inlet port is connected in parallel with function to be operated first . outlet port is connected to function to be operated second . drain line is required to allow internal leakage to return to tank . heck valve is required for rapid return of reversible actuators

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13
Q

the component common to all flow control valves is

A

the orifice

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14
Q

counterbalance valves

A

a safety device used to control the lowering of a vertical load .

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15
Q

the greatest disadvantage of pressure control valves

A

is that a high amount of pressure override is unavoidable when they are passing high rates of oil flow

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16
Q

what is pressure intensification

A

when a restriction on the rod end of a cylinder allows pressure in the system to be greater than normal operating ranges

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17
Q

why can brake valves have a pressure setting less than a counterbalance valve

A

because it is operated by actuator inlet pressure rather than outlet pressure

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18
Q

unloader valves differ from check valves

A

are always used in conjunction with check valves . pilot pressure to open the unloader is sensed from the high pressure side of the check valve

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19
Q

priority flow dividers

A

divert all of the pump oil flow to a primary circuit until flow requirements of that circuit are met . excess flow not required by the primary are delivered to other circuits

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20
Q

what is a (meter out circuit )

A

flow control valve is installed on the return side of a actuator restricting the return oil flow and regulates speed no matter the load acting on it

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21
Q

lock valves are normally not serviceable or adjustable

A

true . a malfunctioning lock valve will result in loss of actuator control or erratic actuator movement . you must replace the valve is any of these conditions exist

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22
Q

counter balance valves do not work well with varying loads because

A

power is wasted opening the valve when loads a are lighter than maximum . static oil pressure in the actuator may open the valve is maximum load is exceeded resulting in a loss of control

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23
Q

back pressure valves

A

are pressure control valves that control actuator movement by restricting return oil from the actuator

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24
Q

pressure control valve applications

A

pressure reliefs . unloader reliefs . pressure reducing valves . sequence valves . backpressure valves

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25
Q

two basic gas filled accumulators are

A

bladder and piston

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26
Q

what is a high low type pump configuration

A

a demand type hydraulic system that provides oil flow in relation to demand on the system . flow rate is high when pressure is low . when load on the system is high flow decreases and pressure rises

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27
Q

the difference between cracking and full flow pressure is known as

A

pressure override

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28
Q

unloader valves are normally pilot operated valves because they must

A

pass full pump flow without excessive override

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29
Q

in a direct acting pressure control valve the force created by hydraulic pressure is directly opposed by

A

spring force

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30
Q

gas filled bladder type accumulators

A

uses a rubber bladder to separate the nitrogen from the oil . oil entering the accumulator acts on the surface area of the bladder compressing the nitrogen and causing pressure to rise . a spring loaded poppet valve in the oil inlet port of the accumulator stops the bladder from being pushed out if gas pressure is higher than oil pressure

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31
Q

what is one of the most significant factors in determining pressure override

A

spring constant of the valve . the greater the spring constant the greater the pressure override

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32
Q

pressure reducing valves

A

are a pressure control that allow one circuit to have a max operating pressure lower than the rest of the system

33
Q

the override pressure of a pilot operated vs a direct acting control valve is much less because

A

the strong spring on the pilot operated only needs to pass a small amount of flow . the majority of the flow passes by the main poppet which is held by a light spring

34
Q

sequence valves

A

cause actions in hydraulic system to happen in a certain order . maintain a predetermined minimum pressure in the primary hydraulic function while secondary is operated

35
Q

similarities to unloader valve and relief valves

A

are always normally closed . inlet port is always connected in parallel with the system or circuit . the outlet is connected to tank

36
Q

three types of accumulators

A

weighted . spring loaded . gas charged

37
Q

weighted accumulators

A

have a piston in a barrel with weights on top . pressure works on the bottom of the piston to overcome the weights and fill the chamber as pressure the weights overcome the oil and force it back out of the chamber

38
Q

excessive pressure override in a system relief would cause

A

the valve to crack within the systems operating pressure causing some of the pump flow to be diverted from the actuators slowing their speed and generating unwanted heat

39
Q

the vast majority of system relief valves are pilot operated because they must be able to

A

pass the full flow rate of the pump with as little pressure override as possible

40
Q

functions and applications of accumulators

A

energy storage . shock absorption . gradual pressure buildup . constant pressure maintenance

41
Q

if the poppet of a relief valve what sticky or seized

A

you would get higher system pressure than normal

42
Q

what is the spring constant

A

indicates the stiffness of a spring

43
Q

hydraulic valves assert their control over the system by

A

controlling pressure . regulating the amount of oil that flows through branches of the system . determining the path that oil flows

44
Q

unloader valves

A

allow full pump flow to return to tank while maintain minimum pressure at the pump outlet . taking the load off the pump and engine driving it

45
Q

what is cracking pressure

A

when pressure has risen just enough to lift the valve off its seat and oil can flow to the outlet port

46
Q

pressure control valves preform the following tasks

A

limit or otherwise regulate pressure . create pressure condition required for control . cause actuators to operate in particular order

47
Q

a pilot valve is designed to deal with

A

high pressure and low flow rates

48
Q

pressure compensated flow control valves

A

maintains a constant flow through its orifice by maintaining a constant pressure drop across it

49
Q

non pressure compensated flow control valves

A

the flow through them varies as the pressure downstream of the flow control changes . they do not accurately control flow because flow varies with the load on the cylinder

50
Q

circuit relief valves protect

A

components from shock loads that produce pressure spikes . and pressure caused by expanding hydraulic oil due to heat

51
Q

gas filled piston type accumulator

A

uses a piston honed to the inside of the accumulator and uses seals to separate it form the oil . as the chamber fills with oil the nitrogen on the other side of the piston is compressed causing pressure to rise

52
Q

back pressure valve characteristics

A

normally closed . pilot pressure to open the valve varies depending on the valve type . back pressure valves are connected in series with the actuator return line . check valve is required to allow reversible actuators to return

53
Q

a pilot operated pressure control valve offers

A

much more accurate pressure control with significantly reduced pressure override

54
Q

lock valve

A

hold a suspended load in the event of a hydraulic line rupture . prevent the load from drifting due to leakage in the directional control valve . prevent the load from over speeding the actuator

55
Q

direct acting pressure control valves are designed to deal with

A

high flow rates and low pressures

56
Q

two basic pressure control valve configurations are

A

direct acting and pilot operated

57
Q

internal leakage in a relief valve could be caused by

A

broken o-ring contamination keeping poppet open damaged poppet seat

58
Q

spring loaded accumulator

A

consists of a large spring in a chamber . as oil pressure rises it overcomes spring pressure and fills the chamber . force acting on the oil from the spring is not constant the more the spring compresses the more force is exerted on the oil

59
Q

two applications for unloader valves are

A

used in a closed center system with a fixed displacement pump . and a type of hydraulic system using tandem fixed displacement pumps

60
Q

gas charged accumulators

A

uses nitrogen gas to exert force on the oil because it will not react with hydrocarbons in the oil

61
Q

two most common applications of relief valves

A

system reliefs and circuit reliefs

62
Q

pressure controls are most often used in applications where

A

they encounter low flow rates and infrequent duty cycles

63
Q

the amount of pressure intensification depends on

A

the amount of restriction in the return line . the ratio of and rod end and base end piston areas . force increase created by the load on the rod end

64
Q

two classifications of pressure control valves are

A

normally closed and normally open

65
Q

system reliefs

A

protect the complete hydraulic system from being damaged by excessive pressure

66
Q

if the poppet of a relief valve was stuck open or the valve spring was broken you would get

A

lower system specification pressure than normal

67
Q

pressure control with excessive override will

A

waste power and generate unwanted heat

68
Q

what is a ( meter in circuit )

A

controls the amount of oil flowing into the base end of a cylinder controlling extension

69
Q

flow dividers

A

split a single flow of oil between two or more actuators

70
Q

hydraulic valves are rated for

A

maximum pressure capability as well as the pressure drop they create when a given flow rate passes through them

71
Q

poppet type normally closed direct acting pressure control valve

A

cone shaped design tends to center it in the oil stream

72
Q

two types of flow dividers

A

priority flow dividers . proportional flow dividers

73
Q

brake valves

A

are used in return line in hydraulic motors to prevent the load from over speeding the motor and provide a controlled deceleration of the load

74
Q

why must you never use oxygen or compressed air to charge a gas filled accumulator

A

because oxygen and air can mix with the hydrocarbons of the oil and cause an explosion

75
Q

proportional flow dividers

A

or more circuits splits a single flow among two circuits .the flow divider is pressure compensated to ensure oil flow is constant regardless of the load on either circuit

76
Q

three categories of hydraulic valves

A

pressure control valves . flow control valves . directional control valves

77
Q

the speed of an actuator is determined by

A

internal capacity . input flow rate

78
Q

a pilot operated pressure control is often called

A

a compound pressure control because it consists of two direct operating pressure controls acting together as one unit

79
Q

circuit relief valves pressure setting is set

A

normally higher than the system relief so they wont crack under normal working pressure

Hydralics (12 decks)

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