Pneumatic systems are simple enough to draw as a chain, which makes them excellent systems for disciplined fault isolation.
SURVIVAL RULE: Trace command, air, valve, motion, and feedback.
Pressure is not the same as flow
A gauge can show normal static pressure while the machine starves during movement. Restrictions, small tubing, clogged filters, failing regulators, leaks, and undersized supply can cause pressure to collapse only when demand rises. Watch pressure during the fault, not just before it.
A cylinder may extend slowly when several other actuators move at once. The local gauge reads normal at idle, then drops sharply during the cycle. That points toward supply/flow rather than cylinder position sensing.
Field habit: Compare pressure at the supply, regulator, and actuator during motion when safe and appropriate.
Common trap: Do not increase plant pressure to compensate for a local flow restriction.
A solenoid command is only one link
For a pneumatic cylinder to move, the controller must command the valve, the solenoid must actuate, the valve spool must shift, air must reach the correct port, exhaust must leave, and the cylinder/mechanism must be free. Each stage can fail independently.
If the valve LED turns on and you hear a click but the cylinder does not move, verify pressure and valve state. If air reaches the cylinder but it stalls, inspect load, mechanical binding, flow controls, and cylinder condition.
Field habit: Trace command → valve → pressure → flow → motion → feedback.
Common trap: Do not replace the cylinder because the end sensor failed to change; the cylinder may never have received air.
Quick check
What should be true at this point in the sequence?
What evidence can prove or eliminate this section of the system?
What changed recently or only under the failing condition?
Leaks matter most when they change function
Small air leaks are common, but not all cause immediate breakdowns. Prioritize leaks that reduce pressure, create unstable actuator motion, prevent vacuum, increase compressor demand, contaminate areas, or indicate damaged tubing. Listen and use approved leak-detection methods during planned checks.
A cracked push-in tube near a moving axis may seal in one position and leak in another, producing an intermittent fault that looks electrical.
Field habit: Mark leak location, machine state, and whether it affects cycle performance.
Common trap: Do not ignore a leak simply because the machine still runs; it can become tomorrow’s downtime and energy waste.
Flow controls and cushions change timing
Cylinder speed is often adjusted by flow controls, and end-of-stroke behavior may use cushioning. If someone turns an adjustment to ‘fix’ a timing issue, the sequence can become unstable. A cylinder that is too slow may time out; one that is too fast may bounce past a sensor or damage mechanics.
When investigating a changed cycle, compare adjustment positions with documented or known-good settings and look for the original reason timing changed.
Field habit: Record changes and return unauthorized adjustments to controlled settings.
Common trap: Do not solve every pneumatic timing problem by opening flow controls fully.
Quick check
What should be true at this point in the sequence?
What evidence can prove or eliminate this section of the system?
What changed recently or only under the failing condition?
Field Exercise
Trace one cylinder from air supply to valve, flow controls, cylinder, and end sensors.