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HET3 > 301Fa: Hydraulic Valves II > Flashcards

301Fa: Hydraulic Valves II Flashcards

1
Q

Two classifications that apply to pressure control valves are:

A
  • Normally open
  • Normally closed

301Fa Pg. 3

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2
Q

A normally closed pressure control will block the flow of oil through the valve when system pressure overcomes valve spring force. (T/F)

A

False

301Fa Pg. 5

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3
Q

For a pressure control valve, the difference between cracking and full flow pressure is known as:

A

Pressure override

301Fa Pg. 6

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4
Q

The main advantage of using a pilot operated pressure control valve is that it:

A

Provides minimum pressure override

301Fa Pg. 8

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5
Q

A relief valve that limits the maximum pressure in one branch of a hydraulic system is called a:

A

Circuit relief valve.

301Fa Pg. 11

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6
Q

What are three safety precautions that must be observed when installing a pressure gauge into a hydraulic system?

A
  • Depressurize the system before installing the gauge.
  • Select a pressure gauge approximately twice maximum system pressure.
  • Be sure all lines and fittings will withstand at least twice maximum system pressure.

301Fa Pg. 14

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7
Q

A hand pump is sometimes used to test system relief valve pressure setting. (T/F)

A

False

Can be used to test circuit releif valve settings

301Fa Pg. 15

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8
Q

What is the function of a hydraulic unloader valve?

A

Allows full pump flow to return to the reservoir while maintaining a minimum pressure at the pump outlet.

301Fa Pg. 24

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9
Q

Which of the following components is not used in a closed centre hydraulic system that is supplied with a fixed displacement pump?

a) Releif valve
b) Unloader valve
c) Accumulator
d) closed centre directional control valve

A

a) Relief valve

An unloader valve would be used

301Fa Pg. 25

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10
Q

The unloader valve in a demand type hydraulic system that is supplied by tandem fixed displacement pumps is open when:

a) Load on the system is high
b) Load on the system is low
c) Load on the engine is low
d) More flow is required

A

a) The load on the system is high.

301Fa Pg. 27

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11
Q

A pressure reducing valve will block oil flow through the valve when pressure upstream of the valve overcomes the valve spring. (T/F)

A

False

Pilot pressure is senced downtream

301Fa Pg. 28

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12
Q

What are two functions of a hydraulic sequence valve?

A
  • Cause funtions to occur in a certain order
  • Maintain a minimum pressure in a primary function while a secondary function is in operation

301Fa Pg. 30

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13
Q

All hydraulic backpressure valves are located in the:

A

Actuator return line

301Fa Pg. 31

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14
Q

Care must be taken not to excessively restrict the flow from the rod end of a double-acting cylinder because:

A

Pressure intensification which could result in damage to system components

301Fa Pg. 44

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15
Q

One of the primary purposes of a hydraulic lock valve is to prevent the load from drifting due to leakage. (T/F)

A

True

301Fa Pg. 36

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16
Q

What is the most appropriate flow control valve circuit for an application where the actuator load changes direction and strength?

A

Meter out flow control circuit

301Fa Pg. 44

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17
Q

The flow control valve that splits a single flow among two or more circuits is called a:

A

Proportional flow control valve

301Fa Pg. 47

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18
Q

What is the function of the priority flow control valve used in heavy equipment steering systems?

A

Provides a relatively constant flow rate to the steering system regardless of fluctuations in steering pressure or engine speed

301Fa Pg. 45

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19
Q

What are three types of hydraulic backpressure valves?

A
  • Counterbalance
  • Brake valve
  • Lock valves

301Fa Pg. 31

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20
Q

What is a hydraulic counterbalance valve used for?

A

The lowering of a vertical load so it does not fall freely

Works well when the load on the cylinder is constant and doesn’t vary.

301Fa Pg. 32

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21
Q

Why do counterbalance valves not work well with varying loads?

A
  • Power is wasted opening the valve when loads are lighter than the maximum
  • Static oil pressure in the actuator may hold the valve open if max load is exceeded

301Fa Pg. 33

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22
Q

How are hydraulic unloader valves different from releif valves?

A
  • Unloader allows full pump flow to tank
  • Always used in conjunction with a check valve
  • Pilot pressure to open the unloader valve is sensed from the high pressure side of the check valve

301Fa Pg. 24

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23
Q

Oil is flowing through an orifice. Where in the circuit is the oil pressure the lowest?

A

Lowest pressure in the orifice

301Fa Pg. 38

24
Q

The amount of oil flow that passes through an orifice is determined by: (3)

A
  • Orifice size and shape
  • Pressure drop across the orifice
  • Viscosity of the oil

301Fa Pg. 39

25
Q

Most hydraulic valves can be classified as one of what three categories?

A
  • Pressure control valves
  • Flow control valves
  • Directional control valves

301Fa Pg. 2

26
Q

A pressure reducing valve is:
a) Normally open
b) Normally closed

A

Normally Open

301Fa Pg. 4

27
Q

What does Spring Constant refer to?

A

The stiffness of a spring. Measured in lbs/inch of compression.

301Fa Pg. 6

28
Q

What is the term that describes when hydraulic pressure has risen just enough to lift a valve off its seat and begins to pass oil to the outlet port?

A

Cracking pressure

301Fa Pg. 6

29
Q

What is the term that describes when hydraulic pressure has risen enough to fully open a valve off its seat and allow full flow through to the outlet port?

A

Full flow pressure

301Fa Pg. 6

30
Q

What is the term that describes the difference between cracking pressure and full flow pressure?

A

Pressure override

301Fa Pg. 6

31
Q

What is the greatest dissadvantage of direct acting pressure control valves when they are passing high flow rates?

A

High amount of pressure override

301Fa Pg. 7

32
Q

What is the basic design of a pilot operated pressure control valve?

A

Two direct operating releif valves that operate together.
Pilot Valve/Poppet: High pressure, low flow
Main Poppet: Low pressure, high flow

Oil flow across the pilot poppet causes a pressure drop across the main poppet. The higher pressure on the inlet side of the main poppet (20-50 psi) is enough to overcome the spring force, shuttle it open, and allow oil to flow through to the outlet port.

301Fa Pg. 8

33
Q

Are pressure relief valves normally open or normally closed?

A

Normally Closed

301Fa Pg. 10

34
Q

Common applications of pressure relief valves include system and circuit relief valves. Which one is usually set higher and why?

A

Circuit relief valves set higher so they do not crack/open during normal operation in the working pressure range of the system.

Designed as protection from shock loads.

301Fa Pg. 11

35
Q

What steps would be taken to adjust a system pressure releif valve?

A
  • Instal a pressure guage
  • Warm up the oil. 150F - 180F
  • Stall an actuator while reading the pressure
  • Adjust releif valve set screw or add/remove shims

301Fa Pg. 14

36
Q

What is the function of a hydraulic pressure reducing valve?

A

Allows one circuit to receive a maximum operating pressure that is less than the maximum operating pressure of the rest of the circuit.

301Fa Pg. 28

37
Q

Hydraulic sequence valves are normally open or closed?

A
  • Normally closed
  • Pilot pressure sensed upstream

301Fa Pg. 30

38
Q

What are hydraulic brake valves used for? (2)

A
  • Prevent a load from overspeeding the motor
  • Provide a controlled deceleration of a load

301Fa Pg. 35

39
Q

What are three main functions of a hydraulic lock valve?

A
  • Hold a suspended load if a line ruptures
  • Prevent a cylinder from drifting
  • Prevent a load from overspeeding the actuator

301Fa Pg. 36

40
Q

A pressure compensated flow control valve maintains constant flow through the valve by:

A

Maintaining a constant pressure drop across its orifice.

301Fa Pg. 41

41
Q

Pressure compensated flow control valves can be classified as either a bypass type or restrictor type. Which one would typically be used in a circuit with a fixed displacement pump?

A

Bypass type

- Excess flows to the reservoir
- Less efficient than restrictor type

301Fa Pg. 41

42
Q

What is used in conjunction with a non-pressure compensated flow control valve to make it a bypass type pressure compensated valve?

A

A compensator

  • Normally closed
  • Downstream pressure assists the spring to close the valve

- Installed in parallel

301Fa Pg. 41

43
Q

How is a compensator used in conjuction with a non-pressure compensated flow control valve to provide an efficient method of regulating flow?

A
  • Connected in series
  • Normally open
  • Downstream pressure assists the spring
  • Upstream pressure acts to close the valve

301Fa Pg. 42

44
Q

Two common applications for restrictor type flow control valves are:

A

Meter In
Meter Out

301Fa Pg. 43

45
Q

What type of flow control valve is shown?

A

Meter In, restrictor type, pressure compensated flow control valve

301Fa Pg. 43

46
Q

What type of flow control valve is shown?

A

Meter Out, restrictor type, pressure compensated flow control valve

301Fa Pg. 43

47
Q

What are two types of hydraulic flow dividers?

A
  • Priority flow divider
  • Proportional flow divider

301Fa Pg. 44

48
Q

What is the basic function of a proportional flow divider?

A

Splits flow between two or more circuits
ie. 50/50 split, or 60/40 split

301Fa Pg. 47

49
Q

What valve is shown by A?

A

Unloader Valve

- Normally closed
- Pilot sensed on high side of check valve

301Fa Pg. 25

50
Q

What valves are shown by A, B, and C?

A

A - Filter Bypass Valve
B - System Releif Valve
C - Circuit Relief Valve

301Fa Pg. 11

51
Q

What valves are shown by A & B?

A

A - System Relief
B - Unloader Valve

301Fa Pg. 27

52
Q

What valve is shown by A?

A

Pressure Reducing Valve

- Normally open
- Pilot pressure to close is sensed dowstream

301Fa Pg. 28

53
Q

What valve is shown by A?

A

Sequence Valve

  • Cause actions to occure in a certain order
  • Maintain a predetermined minimum pressure in the primary function while the second function is in operation

301Fa Pg. 30

54
Q

What valve is shown by A?

A

Counterbalance Valve

- Controls the lowering of a vertical load so it does not fall freely

301Fa Pg. 32

55
Q

What is valve is used in the following diagram?

A

Brake Valve

301Fa Pg. 35

56
Q

What valve is shown by A?

A

Lock Valve

  • Hold a suspended load if a line ruptures
  • Prevent drifting
  • Prevent load from overspeeding the actuator

301Fa Pg. 36

HET3 (36 decks)

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