Hydraulic Pumps And Actuators Exam Review

Question 1

List the three (3) main styles of pumps (based on pumping elements)?

Answer 1

• Piston Pump
• Vane Pump
• Gear Pump

Question 2

What is required at the pump inlet in order for oil to flow into the inlet port?

Answer 2

Pressure Differential.

Question 3

Explain why hydraulic pumps are required to be positive displacement pumps?

Answer 3

To maintain pressure by positive sealing, inlet to discharge. (eliminating backpressure)

Question 4

Explain the difference between a pressure compensation and load sensing in a pump. And Which one is more efficient?

Answer 4

Pressure Compensation Pump: Is to reduce flow, but maintain self operating pressure.

Load Compensating Pump: It adjust pump stroke to maintain only required flow and required pressure drop. plus (200 to 400 psi)

Load Compensating is more efficient.

Question 5

Explain the difference in Operation between an in-line axial piston pump and a bent-axis piston pump?

Answer 5

An in-line piston pump has a swash plates which can be adjusted to an operating degree. The bent-axis has a bent shaft and can be adjusted by a block.

Question 6

Explain the difference in operation between a radial piston pump and a rotary piston pump?

Answer 6

The difference is that the rotary piston pump the pistons are rotating

Question 7

What is the purpose of the intra-vane in a pump? And in what type of vane pump would you find one in?

Question 8

Explain the difference between a balanced cam pump and an unbalanced vane pump?

Answer 8

• Balance Cam Pump: is more compact and has an eccentric cam.
• Unbalanced Vane Pump: Is a variable pump.

Question 9

Explain the differences between an internal gear pump and an external gear pump?

Answer 9

• External Gear Pumps: They have two (2) meshing gears together.
• Internal Gear Pumps: Internal has a crescent seal.

Question 10

Gerotor gear pumps do not have seals. What is required for Gerotor pumps to be a positive displacement pump and where are they found?

Answer 10

• Sliding Creates sealing

* They are found on charged pumps

Question 11

Explain the operation of a cylinder cushion?

Answer 11

It’s purpose is to provide cushion when it hits the end of stroke.

Question 12

Explain the factors that affect torque and speed in hydraulic motors?

Answer 12

======

Question 13

Why should dynamic seals have some leakage?

Answer 13

For Lubrication

Question 14

How can you determine the proper torque value when you are assembling a hydraulic component?

Answer 14

Consult the service manual.

Question 15

What type of sealant should be used on tapered pipe threads in hydraulic systems?

Answer 15

Liquid PTFE (Teflon)

Question 16

When static O-ring gaskets are used, what percentage must they project from the mating surface?

Answer 16

10%

Question 17

What method is used to ensure that you have achieved your target cleanliness code for a hydraulic system?

Answer 17

Use a particle counter

Question 18

Which filter must be rated at the relief valve pressure of the system?

Answer 18

Pressure line filter.

Question 19

What is the recommended micron size filter for a reservoir breather?

Answer 19

3 Microns

Question 20

What is the efficiency of a filter with a Beta Ratio of 10?

Answer 20

90%

Question 21

what is the main purpose of an accumulator?

Answer 21

To store pressurized hydraulic fluids.

Question 22

What extra safety precaution must be taken when working on a system with an accumulator?

Answer 22

Completely depressurize and block out accumulator.

Question 23

Which type of gas could be used in a gas accumulator?

Answer 23

Nitrogen.

Question 24

What is the main disadvantage of a spring type accumulator?

Answer 24

Cannot maintain a constant pressure as they discharge.

Question 25

What component in a reservoir reduces turbulence, aids in cooling, and promotes settling of contaminants?

Answer 25

The Baffle

Question 26

The oxidation rate of petroleum based hydraulic oil doubles every 10°C above?

Answer 26

60°C

Question 27

What condition can occur should the inlet strainer on a pump be clogged?

Answer 27

Cavitation

Question 28

What size is an open circuit reservoir when compared to the capacity of the pump?

Answer 28

2 - 3 times larger

Question 29

What condition can occur should the pump shaft seal fail?

Answer 29

Aeration

Question 30

In addition to transmitting power, what are the other functions must hydraulic fluid must do?

Answer 30

* Lubricate * Cool * Seal * Clean

Question 31

Viscosity Index (VI) of oil is defined as?

Answer 31

Stability of an oil viscosity over a temperature range.

Question 32

Built in contamination in a hydraulic system can happen when?

Answer 32

When the components are assembled and repaired.

Question 33

What is the main cause of oxidation in a hydraulic fluid?

Answer 33

*Heat

Question 34

Which filter location is the most efficient in a hydraulic system?

Answer 34

Permanent off-line

Question 35

A rotating mechanical seal that allows controlled leakage for flushing and cooling purposes would be classified as?

Answer 35

Positive/Dynamic

Question 36

What is the proper accumulator Pre-charge if used for shock absorption purposes?

Answer 36

75% of normal working pressure

Question 37

Cavitation can be the result of?

Answer 37

Running a pump at too high a speed.

Question 38

An example of dynamic pump would be

Answer 38

Impeller

Question 39

A cylinder which is extended by force and retracted by spring or gravity is known as

Answer 39

Single Acting

Question 40

The flow produced by a pressure compensated pump during cylinder extension is at

Answer 40

Load Pressure

Question 41

The flow produced by a pressure compensated pump at the end of stroke is at

Answer 41

No flow produced

Question 42

The purpose of a cylinder cushion is to?

Answer 42

Reduce mechanical shock

Question 43

The pump in a hydraulic system produces?

Answer 43

Fluid Flow

Question 44

An unbalanced vane pump can be identified by its?

Answer 44

Off-Centre cam ring

Question 45

Variable displacement vane pumps control fluid flow by?

Answer 45

Shifting the cam ring

Question 46

The vanes of a pump maintain contact with the cam ring by?

Answer 46

Centrifugal Force / Fluid Pressure

Question 47

A balanced vane pump would have?

Answer 47

Sets of inlet and outlet ports opposing each other

Question 48

The displacement of a bent-axis piston pump can be varied by?

Answer 48

Pivoting the cylinder block to change angle to shaft

Question 49

The torque of hydraulic motor is dependent upon?

Answer 49

Inlet pressure, surface area and radius of rotation

Question 50

If a cylinder had internal leakage it would affect?

Answer 50

Speed

Question 51

Hydraulic motors are driven by?

Answer 51

Fluid flow and pressure

Question 52

Which component prevents contamination from entering a cylinder?

Answer 52

Rod Wiper

Question 53

Which type of cylinder accelerates during extension?

Answer 53

Telescopic

Question 54

Balanced vane motors maintain vane contact by?

Answer 54

Fluid Pressure / Springs

Question 55

In an in-line axial piston motor, speed can be increased by

Answer 55

Decreasing swash plate angle

Question 56

The purpose of a stop tube is?

Answer 56

Reduce side load when extended

Question 57

In a rotary piston pump the fluid is ported in and out of cylinders through the?

Answer 57

Pintle

Question 58

The output flow of gear pumps can be adjusted by

Answer 58

Changing RPM of prime mover

Question 59

A radial piston motor can be classed as?

Answer 59

Low Speed / High Torque

Question 60

O-ring boss port connections have which type of threads?

Answer 60

Straight