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HET3 > 301Fb: Hydraulic Valves II > Flashcards

301Fb: Hydraulic Valves II Flashcards

1
Q

The most commonly used type of directional control valve used in heavy equipment hydraulic systems is the:

a) Poppet
b) Rotary
c) Sliding Spool
d) Check Valve

A

Sliding spool

301Fb Pg. 4

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2
Q

In the float position, the directional control valve connects the work ports to the:

A

Reservoir

301Fb Pg. 9

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3
Q

A directional control valve with a hold position will:

a) Have its work ports open in the neutral position
b) Have its work ports closed in the neutral position
c) Be an open centre valve
d) Be a closed centre valve

A

b) Have its work ports closed in the neutral position

301Fb Pg. 7

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4
Q

Closed centre directional control valves that are supplied by fixed displacement pumps use a relief valve to limit maximum system pressure. (T/F)

A

False.

Would need an unloader valve for a fixed displacement pump, or a variable displacement pump.

301Fb

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5
Q

A pressure regulating pilot control provides accurate directional control valve movement because it regulates:

a) Pilot oil flow to the directional control valve
b) Pump oil flow to the directional control valve
c) Pilot pressure to the directional control valve
d) Pump pressure to the directional control valve

A

c) Pilot pressure to the directional control valve

301Fb Pg. 14

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6
Q

The main disadvantage of electrical directional control valve actuation is that it does not allow feathering of the directional control valve. (T/F)

A

True

301Fb Pg. 18

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7
Q

The component that prevents a suspended load from dropping momentarily when the directional control valve is moved from the hold to the raise position is called:

A

Load check valve.

Prevents a reverse oil flow from the work port to the pump when the spool valve is stroked.

301Fb Pg. 22

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8
Q

What is the function of a hydraulic anti-cavitation check valve?

A

Prevents a void from forming in the actuator when the load drives the actuator faster than the pump can supply it with oil.

301Fb Pg. 23

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9
Q

What are two advantages that directional control valve stacks have over unibody valves?

A
  • Additional functions can be easily added
  • Individual valves can be replaced when it is damaged without needing to replace the whole valve assembly

301Fb Pg. 27

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10
Q

The passage that carries pump oil flow through an open centre directional control valve when it is in neutral is called the:

A

Series Passageway

301Fb Pg. 28

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11
Q

When two functions of an open centre, series-parallel directional control valve are actuated at the same time, how will the actuators react?

A

The actuator with the lightest load will have priority

301Fb Pg. 29

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12
Q

What are three methods of connecting an auxiliary directional control valve into an open centre hydraulic system?

A

Diverter Valve: Selects one valve at a time
Power Beyond Sleeve: Extends series passageway
Flow Divider: Splits flow between multiple control valves

301Fb Pg. 29

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13
Q

When a diverter valve is used to connect an auxiliary directional control valve into an open centre hydraulic system, the main and auxiliary valve can be operated
simultaneously. (T/F)

A

False

301Fb Pg. 30

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14
Q

Auxiliary closed centre directional control valves can be connected into an existing closed centre hydraulic system by connecting the auxiliary valve in:

a) Series
b) Parallel
c) Series- Parallel
d) Tandem

A

Parallel

301Fb Pg. 31

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15
Q

What is the difference between electrical and electronic hydraulic directional control valve actuation?

A

Electrical: On/Off spool movement
Electronic: Infinitely variable spool movement through PWM signals

301Fb Pg. 18

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16
Q

If a spool valve is badly scored and has excessive internal leakage, what is the best repair?

a) Polish out the scores on the spool valve and housing
b) Replace the entire valve
c) Replace just the spool
d) Replace just the valve housing

A

Replace the entire valve.
Valve spools and housings are most commonly mated items and should not be interchanged.

301Fb Pg. 3

17
Q

What is depicted on the spool in the diagram?

A

Metering notches cut on the edge of the lands to allow feathing of the control valve.

301Fb Pg. 5

18
Q

Hydraulic spool valves are often machined with grooves around the circumference of the lands. What two purposes do these serve?

A
  • Trap oil for lubrication and sealing
  • Center the spool as oil acts equally around the circumference of the spool

301Fb Pg. 5

19
Q

For a hydraulic valve, the number of “ways” refers to:

A

The number of connections there are to the valve

20
Q

Why would a brake valve be installed on the outlet side of a hydraulic motor?

A
  • Control deceleration and hold the motor when control valve is moved to centre
  • Prevent shock loads
  • Prevent load drift

301Fb Pg. 11

21
Q

What is a benefit of using electric-over-pilot control valve actuation in a hydraulic system?

A
  • Easy and economincal remote control
  • Generate greater force than an electric only actuation

301Fb Pg. 17

22
Q

What is used in conjunction with electromagnetic detents in a hydraulic directional control valve which controls when the spool is released, allowing it to return to centre?

A

Proximity Switch

Energizes the relay that controls the electromagnet

301Fb Pg. 20

23
Q

What type of configuration does the following system utilize?

a) Series
b) Parallel
c) Tandem Centre
d) Series-Parallel

A

Tandem Centre

The return oil from one actuator is directed back into the series passageway rather than back to the tank.

301Fb Pg. 28

24
Q

What type of directional control valve is used in the folowing diagram?

A

Float Centre
3 position, 4 way
Spring centred
Lever actuated

(With brake valves for the motor)

301Fb Pg. 11

25
Q

What type of control valves are used in the following diagram?

A

Pilot:
- 3 position, 4 way
- Float centre
- Lever actuated, spring centred

Main:
- 3 position, 4 way
- Closed centre
- Hydraulic pilot actuated, spring centred

301Fb Pg. 14

26
Q

What is shown by A?

A

Anti-cavitation check valve

301Fb Pg. 23

27
Q

What is shown by A and B?

A

A - Pressure Compensator
B - Double Check Valves

- Very accurate flow control
- Constant pressure drop across spool

301Fb Pg. 25

HET3 (34 decks)

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