433A Pneumatic Systems 4 — Questions and Answers
Question 1: How does a pneumatic cylinder cushion work?
- It adds foam padding to the cylinder
- It traps exhaust air near the end of stroke and meters it through an adjustable orifice to decelerate the piston gradually (Correct answer)
- It reduces the air supply pressure at end of stroke
- It uses a spring to slow the piston
Correct answer: It traps exhaust air near the end of stroke and meters it through an adjustable orifice to decelerate the piston gradually
End-of-stroke cushioning uses a cushion spear or piston nose that enters a cushion seal near the end cap, trapping the remaining exhaust air. This trapped air is forced through an adjustable needle valve, creating a controlled deceleration of the piston before it reaches the end cap.
Question 2: What is the purpose of a pneumatic timer valve?
- To display the current time
- To create a time delay in a pneumatic circuit by slowly charging or exhausting a small reservoir through a needle valve (Correct answer)
- To measure how long the system has been running
- To synchronize multiple compressors
Correct answer: To create a time delay in a pneumatic circuit by slowly charging or exhausting a small reservoir through a needle valve
A pneumatic timer valve creates a timed delay by using a needle valve to slowly fill or empty a small air reservoir. When the reservoir reaches sufficient pressure, it shifts a valve or sends a pilot signal, introducing a time delay in the circuit sequence.
Question 3: What is a vacuum generator (venturi) and how does it work in pneumatic systems?
- It generates electrical power from vacuum
- It uses compressed air flowing through a venturi nozzle to create suction (vacuum) for gripping and holding applications (Correct answer)
- It removes air from a sealed container
- It increases compressed air pressure
Correct answer: It uses compressed air flowing through a venturi nozzle to create suction (vacuum) for gripping and holding applications
A pneumatic vacuum generator uses the Venturi effect — compressed air flowing through a constriction creates a low-pressure zone that generates vacuum. This vacuum is used for suction cups, material handling, and pick-and-place applications.
Question 4: What is the effect of oversizing pneumatic lines and fittings?
- Increased pressure drop
- Lower pressure drop but potentially higher installation cost with no additional benefit beyond the optimal size (Correct answer)
- Faster cylinder speeds
- Increased moisture in the system
Correct answer: Lower pressure drop but potentially higher installation cost with no additional benefit beyond the optimal size
Oversized lines reduce pressure drop, which is beneficial up to a point, but beyond the optimal size, the additional cost of larger fittings and tubing provides no meaningful improvement in performance. The extra volume can also slow response time.
Question 5: Why should thread sealant tape (PTFE tape) be applied carefully to pneumatic fittings?
- To make the fittings look professional
- Because loose tape fragments can break off and enter the system, blocking orifices and damaging valve seats (Correct answer)
- To increase the pressure rating of the fitting
- PTFE tape should never be used on pneumatic fittings
Correct answer: Because loose tape fragments can break off and enter the system, blocking orifices and damaging valve seats
PTFE tape must be applied neatly, starting 1-2 threads back from the end, wrapped in the correct direction, and trimmed cleanly. Loose strands can shear off during assembly and enter the air system, blocking small orifices in valves and instruments.
Question 6: What is the function of a soft-start (slow-start) valve on a pneumatic system?
- To reduce compressor startup noise
- To gradually increase air pressure to the system during startup, preventing sudden uncontrolled actuator movement (Correct answer)
- To soften the impact of cylinder end strokes
- To warm up the compressed air
Correct answer: To gradually increase air pressure to the system during startup, preventing sudden uncontrolled actuator movement
A soft-start valve slowly ramps up the air pressure to the downstream system during startup, preventing cylinders and actuators from making sudden, uncontrolled movements when the system is first pressurized — an important safety feature.
433A Pneumatic Systems 4
How does a pneumatic cylinder cushion work?