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Millwright Third Year 2018 > Hydraulic Pumps And Actuators > Flashcards

Hydraulic Pumps And Actuators Flashcards

1
Q

Do Pumps Create Pressure or flow?

A

Flow.

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2
Q

Why are positive displacement pumps used for hydraulics?

A

Because flow is not affected by backpressure.

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3
Q

Does the volume of the pumping chambers expand or contract at the inlet?

A

Expands.

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4
Q

List three (3) methods of changing the output of a pump?

A
  • Built-in flow control and relief
  • Drive speed change
  • Variable displacement
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5
Q

If a pump is mounted above the surface of the liquid, what provides the pressure to push the fluid up into the pump?

A

Atmospheric Pressure.

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6
Q

What are three (3) ways to push fluid into a pump besides using atmospheric pressure?

A
  • Gravity
  • Pressurized Reservoir
  • Charge Pump
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7
Q

How is the stroke increased on an axial piston pump?

A

By increasing the swash plate angle.

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8
Q

Which swash plate control limits the maximum pressure in the system?

A

Pressure Limiting Compensator.

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9
Q

Which swash plate control regulates the flow to suit any given load?

A

Load Sensing Compensator.

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10
Q

What is the main reason for using the pressure compensator and the load sensing compensator?

A

To Save Energy

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11
Q

What would happen if you set the load sensing compensator at zero psi?

A

There would be no pressure to operate the bias piston and it would bring the pump back to full stroke.

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12
Q

What must you do to a new or rebuilt pump before you install it?

A

Fill the case with fluid?

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13
Q

How can you increase the stroke on a bent axis piston?

A

Increase the cylinder block angle to the shaft axis.

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14
Q

Which component of a rotary piston pump port the fluid in and out of the cylinders?

A

The Pintle.

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15
Q

How can you increase the flow from a rotary piston pump?

A

Move the reaction ring farther off centre.

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16
Q

Which part of a radial piston pump drives the piston?

A

An eccentric drive cam.

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17
Q

Does the space between the vane increase or decrease at the inlet?

A

Increases.

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18
Q

How is the output flow increased on an unbalanced vane pump?

A

By moving the cam ring off centre.

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19
Q

What two (2) Methods are normally used to hold the vane out against the cam ring on a vane pump?

A
  • Centrifugal Force

* Fluid Pressure Under The Vanes

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20
Q

Which type of pump is more compact? Balanced vane or the unbalance vane?

A

Balanced Vane

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21
Q

What is the rotation of a factory rebuilt balanced vane pump?

A

Right Hand.

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22
Q

From which end of the pump is the direction of rotation defined?

A

Drive End.

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23
Q

How do you change the direction of rotation in a balanced vane pump?

A

Flip over the cam ring, rotor and flex plate assembly.

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24
Q

Name three (3) indications of contamination damage in a vane pump?

A
  • Marks around the inside of the cam ring.
  • Frosted appearance on the vanes.
  • Circular marks on the flex plates.
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25
Q

Name two (2) indications of cavitation or aeration damage in a vane pump?

A
  • Ripple marks inside the cam ring.

* Erosion at the ports.

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26
Q

On a gear pump, do the teeth go into or come out of mesh at the inlet?

A

Out Of Mesh.

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27
Q

What determines the volumetric efficiency of a gear pump?

A

The close fit between the gears, and between the gears and the casing and wear plates.

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28
Q

Why do gear pumps require heavy needle bearings?

A

Because they are hydraulically unbalanced, so the bearing must support high radial loads.

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29
Q

If the crescent seal in an internal gear pump becomes worn, what happens to the flow inside the pump?

A

Some of the discharge flow recirculate back to the inlet.

30
Q

How can you change the output of a gear pump?

A

By changing the speed of the driver.

31
Q

Name two (2) symptoms of wear from contamination in gear pumps?

A
  • Wear plates scored.

* Sharp edges on tips of the gears.

32
Q

What can you do to repair a gear pump if only the wear plates are scored and the tips of the teeth have sharp edges?

A

Change the wear plates and stone off the sharp edges.

33
Q

What is the maximum efficiency that you can expect from a new gear pump?

A

85%

34
Q

What is the basic operating principle of any positive displacement pump

A

Pumping chambers increase in volume at the inlet and then decrease as they push the fluid out the discharge ports.

35
Q

What, if any, change should you expect in the output of a positive displacement pump as the backpressure increases?

A

Small Decrease.

36
Q

why is it better to locate a pump below the level of the fluid than above the surface?

A

More pressure is available to ensure adequate inlet flow?

37
Q

What condition occurs when the inlet flow is less than the discharge?

A

Cavitation.

38
Q

List three (3) methods of ensuring adequate inlet flow?

A
  • Gravity
  • Pressurized Reservoir
  • Charge Pump
39
Q

Why is it worthwhile to examine a pump that you are about to replace?

A

To determine the root cause of failure.

40
Q

How is the flow rate from an in-line axial piston pump increased?

A

By increasing the swash plate angle.

41
Q

What is the purpose of the bias piston in a in-line axial piston pump?

A

To move the swash plate angle.

42
Q

Which is the best pump to use if you have to locate it above the surface of the fluid; an in-line axial piston pump or a bent axis pump?

A

Bent Axis Pump.

43
Q

How is the fluid ported in and out of a radial piston pump?

A

Through check valves in the pistons.

44
Q

Does the space between the vanes and the cam ring increase or decrease at the discharge port in a vane pump?

A

It Decreases.

45
Q

How many inlet ports and how many discharge ports would you see in a balanced vane pump flex plate?

A

Two Inlet and Two Outlet.

46
Q

Which direction of rotation are factory rebuilt or new balanced vane pump assembled for?

A

Right Hand.

47
Q

List two (2) root causes of heat discoloration on a cam ring that you should check?

A
  • Aeration.

* Poor Quality Fluid.

48
Q

Why is a very tight fit necessary between the teeth and the casing on a gear pump?

A

To prevent bypassing back to the inlet.

49
Q

On an internal gear pump, should the inside gear have the same number of teeth as the outside gear or should it have fewer teeth?

A

Fewer Teeth.

50
Q

Should you expect a new gear pump to be more efficient or less efficient than a piston pump?

A

Less Efficient.

51
Q

What is a double acting cylinder?

A

A cylinder that exerts force in both directions.

52
Q

Which seals are contained in the rod bushing?

A

Rod wiper seals and pressure seals.

53
Q

What is caused by failed rod seals?

A

Dirt and air get into the system.

54
Q

Which type of piston rings would you use if no creep could be tolerated?

A

Synthetic.

55
Q

State two (2) reasons for using cast iron piston rings?

A
  • Higher Temperatures

* Higher Pressures

56
Q

Under what operating condition would you use cylinder cushions?

A

When the load can force the piston to hit the end of the cylinder.

57
Q

When would you required a cushion bypass?

A

If the cylinder is loaded as it begins its stroke.

58
Q

When would you need a stop tube?

A

When the rod has a long extension with some side load.

59
Q

Why is an ORB fitting preferable to a tapered thread fitting?

A

It causes less stress and distortion.

60
Q

Should you normally install a cylinder with the ports at the top or at the bottom?

A

At the top.

61
Q

Why is it important to align a cylinder with the load to which it is attach?

A

To avoid undue wear on the cylinder walls and on the seals.

62
Q

What is the most costly result of leaks in a cylinder?

A

Dirt and air get sucked into the system and damage components throughout the system.

63
Q

How can you detect an internal leak in a cylinder?

A

By hot spots.

64
Q

What is the operating principle of any hydraulic motor?

A

Fluid pushes on vanes, gear teeth or pistons to turn the drive the shaft.

65
Q

Which three (3) types of motors are used for low speed and high torque?

A
  • Radial Piston.
  • Cam-Type Radial Piston.
  • Roller Vane Gerotor.
66
Q

Which type of motor can only turn part of a rotation?

A

A limited rotation motor.

67
Q

Which type of limited rotation motor can be used for clamping?

A

Cylinder with bell crank.

68
Q

Which three (3) specifications determine the torque in a motor?

A
  • Inlet Pressure
  • Surface Area Of The Motor Elements
  • The Radius Of Rotation
69
Q

What does a decease in mechanical efficiency indicate?

A

An increase in internal friction.

70
Q

What does a decrease in volumetric efficiency indicate?

A

Internal Leakage.

71
Q

On which two (2) factors does motor speed depend on?

A
  • Displacement

* Flow Rate

72
Q

Open loop hydra

A

3/4

Millwright Third Year 2018 (15 decks)

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