ITMC Pneumatic Systems 4 — Questions and Answers
Question 1: In a meter-out flow control configuration, the restrictor is placed:
- On the inlet (supply) side of the actuator port
- On the exhaust side of the actuator port (Correct answer)
- Between the compressor and the receiver
- Upstream of the directional control valve
Correct answer: On the exhaust side of the actuator port
Meter-out restricts exhaust flow leaving the cylinder port, providing smoother speed control especially under varying loads.
Question 2: A pneumatic system operates at 90 PSI. A cylinder with a 3-inch bore extends against a 500 lb load. What force does the cylinder generate? (π ≈ 3.14)
- Approximately 424 lbs
- Approximately 636 lbs (Correct answer)
- Approximately 848 lbs
- Approximately 254 lbs
Correct answer: Approximately 636 lbs
Force = Pressure × Area = 90 PSI × (π/4 × 3²) = 90 × 7.07 ≈ 636 lbs, which exceeds the load so the cylinder will extend.
Question 3: What is the purpose of a pilot-operated check valve in a pneumatic holding circuit?
- To prevent pressure from exceeding set limits
- To lock an actuator in position and release it only when pilot pressure is applied (Correct answer)
- To sequence two cylinders automatically
- To reduce air consumption during idle periods
Correct answer: To lock an actuator in position and release it only when pilot pressure is applied
A pilot-operated check valve blocks flow in both directions until a pilot signal unlocks it, allowing a cylinder to be held firmly in position.
Question 4: Compressor oil carryover into the air distribution system is MOST damaging to which component?
- Steel receiver tanks
- Metal air lines and fittings
- Rubber and polyurethane seals and tubing (Correct answer)
- Pressure gauges
Correct answer: Rubber and polyurethane seals and tubing
Petroleum-based compressor oil degrades rubber and polyurethane seals and tubing, causing swelling, softening, and eventual failure.
Question 5: Which diagnostic tool is MOST effective for locating pneumatic system leaks?
- Infrared thermometer
- Ultrasonic leak detector (Correct answer)
- Digital pressure gauge
- Clamp-on ammeter
Correct answer: Ultrasonic leak detector
Ultrasonic detectors sense the high-frequency sound generated by air escaping through leaks, allowing precise location even in noisy environments.
Question 6: A solenoid-operated valve fails to shift when energized. After confirming 24VDC is present at the coil, the next diagnostic step is:
- Replace the entire valve assembly
- Check current draw of the coil and inspect for a burned-out or open coil winding (Correct answer)
- Increase system pressure by 20 PSI
- Replace the directional control valve manifold
Correct answer: Check current draw of the coil and inspect for a burned-out or open coil winding
Voltage present but no valve movement suggests the coil may be open-circuit (burned out) — measuring current draw or coil resistance confirms this.
Question 7: What is the recommended orientation for installing an FRL (Filter-Regulator-Lubricator) assembly?
- Any orientation since they are omnidirectional
- Horizontal mounting with bowl facing down for proper drainage (Correct answer)
- Vertical with inlet at the top
- Angled 45° to reduce pressure drop
Correct answer: Horizontal mounting with bowl facing down for proper drainage
FRL units must be mounted vertically with bowls hanging down so condensate drains by gravity and can be drained from the drain petcock.
ITMC Pneumatic Systems 4
In a meter-out flow control configuration, the restrictor is placed: