Hydraulic Actuator Fundamentals

Question 1

Pressurized oil is allowed to flow past the piston to the rod side of a ram type cylinder.
True
False

Answer 1

True

Question 2

Double acting cylinders are often referred to as differential cylinders because:

Answer 2

there is a difference in the speed and forces generated by extension versus retraction.

Question 3

Leaking piston seals in a differential cylinder result in:
A. Increased cylinder cycle times.
B. Cylinder drifting in the extension direction.
C. Pressure intensification when in the hold position.
D. All of the above.

Answer 3

D. All of the above.

Question 4

A cylinder with piston area of 186cm^2 is supporting a load of 32,000KG.
A. What hydraulic pressure is required to support the load?
B. What pressure is required to support the load if the piston packing are leaking and the cylinder rod area is 62cm^2?

Answer 4

A. 16.86MPA

B. 50.6MPA

Question 5

What causes the difference in pressures that you calculated in the question above?

Answer 5

Leaking piston seals allow pressure to act on the area of the piston on the rod side, nullifying an equal area on the base side of the piston. The load is being supported by an area equal to the area of the rod. This condition is known as pressure intensification.

Question 6

The purpose of a piston relief valve is to:

Answer 6

Allow pump oil flow to bypass the piston when the piston reaches the end of its stroke, reducing heat generation.

Question 7

The quick drop valve used on dozer cylinders provides regeneration when the operator selects:
A. The full raise position.
B. The full lower position.
C. A feathered lower position.
D. Down pressure on the dozer blade.

Answer 7

B. The full lower position.

Question 8

One factor that does not influence motor torque generation is:
A. Inlet flow rate.
B. Inlet pressure.
C. Motor displacement.
D. All of the above.

Answer 8

A. Inlet flow rate.

Question 9

Why are the external gear motors such poor torque generators?

Answer 9

Due to counteracting forces torque is generated by inlet pressure acting on the surface area of just one tooth.

Question 10

Gerotor motors require a spool valve to:
A. Regulate internal pressure.
B. Direct the flow of oil to and from the valleys in the gerotor element.
C. Control the direction of motor rotation.
D. Regulate motor speed.

Answer 10

B. Direct the flow of oil to and from the valleys in the gerotor element.

Question 11

Why must some vane motors be equipped with spring loaded vanes?

Answer 11

Spring loaded vanes are used to ensure good vane to cam ring contact at startup.

Question 12

Pressure compensated, variable displacement motors vary their displacement in response to change in motor load. As the load on the motor output shaft increases, the motor displacement:
Increases
Decreases

Answer 12

Increases

Question 13

Telescoping cylinders offer the following advantage:

Answer 13

Additional stroke length is gained from a relatively compact retracted package.

Question 14

The difference between a differential and non differential cylinder is that:

Answer 14

non differential cylinders have equal piston area and equal volume on both sides of the cylinder.

Question 15

The function of a cylinder rod wiper is to:
A. Prevent oil from leaking pas the cylinder rod.
B. Prevent oil from leaking past the piston.
C. Prevent contamination from entering the cylinder.
D. Prevent air from leaking into the cylinder.

Answer 15

C. Prevent contamination from entering the cylinder.

Question 16

In reference to hydraulic cylinder operation, the term regeneration refers to:

Answer 16

Supplementing pump oil flow to the base end of a double acting cylinder with oil flow from the rod end which increases cylinder extension speed.

Question 17

The speed of a motor driveshaft depends upon:

Answer 17

A. Inlet flow rate.

B. Motor displacement.

Question 18

Most motors are equipped with a drain line that carries:
A. Return oil from the motor to the reservoir.
B. Inlet oil flow to the motor.
C. Leakage oil from the motor to the reservoir.
D. Pilot pressure to the motor.

Answer 18

C. Leakage oil from the motor to the reservoir.

Question 19

Gerotor motors are considered to be high speed low torque motors.
True
False

Answer 19

False

Question 20

Balanced vane motors are good torque generators because:
A. They offer less resistance to flow than other types of vane motors.
B. They are more efficient than other types of vane motors.
C. They can operate at higher pressures than other types of vane motors.
D. They are equipped with a heavier driveshaft and bearings than other types of vane motors.

Answer 20

C. They can operate at higher pressures than other types of vane motors.

Question 21

The main difference between variable and fixed displacement motors is that their speed and torque characteristics will change as their displacement changes.
True
False

Answer 21

True

Question 22

Why are variable displacement motors prevented from reaching the zero displacement positon?

Answer 22

The motor will hydrostatically lock and freewheel in the zero displacement position.