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Millwright 3rd Year 2025 > Hydraulics > Flashcards

Hydraulics Flashcards

1
Q

Which cartridge valve is best for LOW flow (less than 35 gpm

A

Screw in Cartridge valves

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2
Q

What cartridge valve is best suited for high flow?

A

Slip in

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3
Q

What Valve should be mounted first on the subplate in a stack valve assembly

A

Pressure relief valve

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4
Q

What are ways?

A

Ways refer to number of connections

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5
Q

What are cartridge valves mounted to?

A

Manifold block

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6
Q

What are the advantages of stack valves

A

Mounted together, with no external plumbing, very compact, eliminate potential leak point in external plumbing

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7
Q

What are the advantages of Proportional Valves?

A

Controlled electronically
Greater accuracy and control
Simpler circuit design
Ideal for applications that can use electronic control without accuracy of servo valve
More rugged and dirt tolerant than servos valves

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8
Q

What is spool overlap?

A

Where the spool land is larger than the port is wide.

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9
Q

What are advantages of metering notches on a valve spool?

A

Accurate control of speed
Wider speed ranges than solid spool
Can minimize Valve overlap
Soft Shifting ; slower buildup of pressure, preventing shock

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10
Q

What is dead band?

A

No flow through the valve

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11
Q

How is dead band reduced?

A

Spoke to boost power in the solenoid to minimize lag

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12
Q

What is gain?

A

Ratio between input signal and the larger output current flow
Eg output/input

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13
Q

What is a ramp function?

A

Ramp function controls how fast the current and voltage to solenoid is increased and decreased ( acceleration, deceleration)

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14
Q

What is the dither signal?

A

A small high frequency alternating current applied to solenoid to move it rapidly back and forth to reduce any hysteresis (hang up)

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15
Q

What is an open loop system?

A

A system where the controller cannot sense how accurately the actuator is responding to the control setting

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16
Q

What is the most expensive feedback system?

A

Closed outer loop system

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17
Q

Where is a nozzle pressure control normally found?

A

As a pilot stage on PCV’s or for controlling compensator settings on a pressure compensated Variable Displacement Pump

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18
Q

Where is a plate pressure control Valve commonly used?

A

In injection moulding machines to provide smoother control

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19
Q

Why is a plate pressure control valve desirable?

A

They are highly responsive and accurate as they do not need springs to control pressure

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20
Q

What are the advantage of a nozzle pressure control

A

Small nozzle, small flow
Used as pilot stage for other valves
Very accurate
Can be controlled from plc

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21
Q

What are the advantages of a servo valve?

A

More accuate than other pressure control valves, built in feedback loop
More precise

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22
Q

What are the disadvantages of a servo valve?

A

Less rugged and dirt tolerant, must have a pressure line filter installed before servo
More expensive

23
Q

What are the 3 ways to change output on a hydraulic pump

A

Flow controls, changing the speed of the driver, and using a variable displacement pump

24
Q

What is the formula for volumetric efficiency?

A
25
Q

Where is the overall efficiency of a pump relatively low?

A

Lower pressures and max pressures

26
Q

What are the four types of piston pumps?

A

In line axial piston pump
Bent axis piston pump
Rotary piston pump
Radial piston pump

27
Q

What is the most common piston pump?

A

In line axial piston pump Rotary

28
Q

In line axial pumps can be….

A

Fixed displacement
Variable displacement
Pressure compensated or
Load sensing

29
Q

What are the 3 MAIN types of hydraulic pumps

A

Piston pumps
Vane pumps (which can be balanced of unbalanced)
Gear pumps (internal or external)

30
Q

What are the main parts of an in line axial pump

A

The cylinder block,
The swash plate
A shoe plate
A valve plate
The drive shaft
And a case

31
Q

In what plate does the wash plate create no flow?

A

Perpendicular or 0 degree angle

32
Q

What is the purpose of a pressure limiting compensator?

A

To save energy and pump wear when flow is not required

33
Q

What component is combined with a pressure limiting compensator

A

Load sensing compensator
To increase efficiency and save energy when moving loads

34
Q

What hydraulic pump would you use for year round operation?

A

A bent axis pump
(More reliable, built for continuous operation)

35
Q

Why is a bent axis piston pump more reliable than an axial piston pump?

A

No swash plate, or piston shoes
Pistons have ball joints at the ends eliminating potential wear

They can also withstand high vacuum inlet pressures

36
Q

How can you change displacement on a rotary piston pump?

A

You can change displacement by moving the reaction ring

37
Q

Where are rotary piston pumps used?

A

Small Hydrostatic transmissions and applications requiring large volumes (eg 200 cubic inches of displacement)

38
Q

What is a key difference between rotary and radial piston pumps?

A

Radial pumps use a stationary block whereas rotary pumps use a dynamic block and stationary pintle

39
Q

What application would you find a radial piston pump?

A

Low flow, high pressure equipment, such as plastic injection molding machines. These pumps are capable of operating at pressures up to 10,000 psi

40
Q

What is the main disadvantage of an unbalanced vane pump?

A

The casing and bearings must be fairly large to support the large radial thrust loads

41
Q

What is the difference between balanced and unbalanced vane pumps?

A

Balanced vane pumps are fixed displacement, with 2 inlets and 2 outlets offset from the other by 180 degrees, they also have an elliptical shape

42
Q

How do you differentiate from a vane pump and a vane motor

A

Motors have SPRINGS inside

43
Q

How can you increase efficiency in a vane pump?

A

Intra-vane design combined with equalizer holes increase efficiency and reduce wear

44
Q

What are the common causes of failure on vane pumps?

A

Contamination (look for tip wear, frosted appearance, circumferential marks falling on inside of cam ring, circular scoring of flex/support plates

And cavitation or aeration damage
(Ripple marks inside cam ring, erosion at fish tail grooves at inlet/outlets)

45
Q

In unbalanced vane pumps, what does the maximum volume stop do?

A

Restricts movement of the ring

46
Q

What are the main disadvantages of gear pumps?

A

Unbalanced design, and no support for variable displacement

47
Q

What are the 2 types of gear pumps

A

External gear and internal gear

48
Q

What are the 3 gear cuts used in gear pumps?

A

Spur gear, helical gear, and herringbone gears

49
Q

What are the advantages of spur gears in a gear pump

A

Cheap, dirt and contaminant tolerant but are also the noisiest

50
Q

What are the 2 types of internal gear pumps?

A

Crescent pumps and gerotor

51
Q

What is the difference between crescent pumps and gerotor pumps

A

Gerotors have a star shaped rotor with one less tooth than the gear, crescent pumps have a crescent seal that provides a positive seal between suction and discharge

52
Q

What are the characteristics of a gerotor pump

A

Quietest running, least dirt tolerant, can be used as a charge pump

53
Q

The efficiency of a gear pump is dependent on…

A

Close fit of teeth to casing and close fit of teeth to end plates, wear of these plates will allow recirculation

54
Q

Is a gear pump more volumetrically efficient than a piston pump?

A

No, gear pumps peak at 85% volumetric efficiency, whereas piston pumps are 90-95% efficient

Millwright 3rd Year 2025 (4 decks)

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