CPM Hydraulic and Pneumatic Systems 2 — Questions and Answers
Question 1: A hydraulic cylinder has a 4-inch bore and the system pressure is 1,000 psi. What is the approximate extension force?
- 4,000 lbf
- 12,566 lbf (Correct answer)
- 3,142 lbf
- 16,000 lbf
Correct answer: 12,566 lbf
Force = pressure × area = 1,000 psi × (π × 2² = 12.57 in²) ≈ 12,566 lbf.
Question 2: Why does a double-acting cylinder retract with less force than it extends at the same pressure?
- The rod side has higher friction from the wiper seal
- Return flow passes through the filter
- The rod reduces the effective piston area on the rod side (Correct answer)
- The pump delivers less flow during retraction
Correct answer: The rod reduces the effective piston area on the rod side
The rod occupies part of the piston face, so the annular area on the rod side is smaller and gives less force.
Question 3: In a meter-out flow control circuit, where is the flow control valve placed?
- In the line leaving the actuator, restricting exhaust flow (Correct answer)
- In the pump suction line
- In the line feeding the actuator inlet
- In the case drain line
Correct answer: In the line leaving the actuator, restricting exhaust flow
Meter-out restricts fluid leaving the actuator, which gives good control of overrunning loads.
Question 4: A gear pump makes a loud rattling, gravel-like noise and the reservoir oil looks normal. What is the most likely cause?
- Relief valve set too high
- Cavitation from a restricted or clogged suction line (Correct answer)
- Worn directional valve spool
- Low accumulator precharge
Correct answer: Cavitation from a restricted or clogged suction line
A restricted inlet starves the pump, forming vapor bubbles that collapse and cause a gravel-like noise.
Question 5: What is the main purpose of a pilot-operated check valve in a cylinder circuit?
- To raise system pressure above relief setting
- To filter pilot oil
- To divide flow evenly between two cylinders
- To hold a load in position until pilot pressure opens it for reverse flow (Correct answer)
Correct answer: To hold a load in position until pilot pressure opens it for reverse flow
A pilot-operated check blocks reverse flow to lock the load until pilot pressure unseats it.
Question 6: In a compressed air system, where should a branch line be taken off the main header?
- From the top of the header (Correct answer)
- From the bottom of the header
- From the side at the lowest point
- Directly at the receiver drain
Correct answer: From the top of the header
Taking branch lines off the top keeps condensate in the header from running into the drops.
Question 7: What is the function of the lubricator in a pneumatic FRL unit?
- Remove water from the air
- Reduce supply pressure
- Add a fine oil mist to the air for downstream components (Correct answer)
- Silence exhaust noise
Correct answer: Add a fine oil mist to the air for downstream components
The lubricator puts atomized oil into the air stream to lubricate valves and cylinders downstream.
