Insight October/November 2026 www.pwemag.co.uk Plant & Works Engineering | 11 The Compressed Air and Gas Institute explains in its pressure-drop guidance that losses accumulate through piping, filters, dryers, fittings and other restrictions. The British Compressed Air Society also recommends examining compressed-air distribution as a complete system. A large difference between upstream and actuator pressure during motion can indicate undersized tubing, excessive length, restrictive fittings, a blocked filter or inadequate branch capacity. Raising plant pressure may conceal the symptom while increasing energy use and stress elsewhere, so it should not replace diagnosis. Compare extension and retraction A double-acting cylinder does not behave identically in both directions. The effective piston area changes because of the rod, and each stroke uses a different valve passage, tube and exhaust route. Compare extension and retraction times under the same controlled conditions. Then check the supply and exhaust sides associated with the slower direction. Meter-out flow controls are commonly used to stabilise speed, but a misadjusted or contaminated control can restrict movement. An exhaust silencer can also load with oil, dust or water and create backpressure. A practical pneumatic circuit troubleshooting checklist identifies tubing size, speed controllers, load variation and supply conditions among the points to verify when cylinder speed is unstable. Any adjustment should be documented so the original setting is not lost. Follow the entire flow path Trace air in sequence from the local shut-off and regulator to the filter, valve, fittings, tubing, flow controls and cylinder ports. Look for kinked tube, damaged push-in fittings, long runs, small internal diameters and sharp changes in direction. Confirm that the directional valve is receiving a reliable pilot signal and shifting fully. A valve can energise electrically without providing full pneumatic flow if its spool is contaminated or mechanically restricted. Inspect the exhaust path with the same care as the supply path. A plugged silencer or restricted exhaust fitting can slow the opposite cylinder stroke and may be missed when attention stays on inlet pressure. Before removing components, isolate and depressurise the system according to the machine manufacturer’s instructions and the site’s safety procedure. Live diagnostic tests should be planned and performed by qualified personnel under controlled conditions. Check air quality and idle-time behaviour Compressed air can carry particles, water and oil. ISO 8573-1 defines purity classes for these contaminants, but the appropriate class depends on the application and equipment requirements. A filter bowl that appears acceptable at a glance does not prove that the air reaching a valve is dry or clean under all operating conditions. Guidance on compressed-air contamination describes how dirt, water and oil can affect pneumatic components. Check drains, filter condition, dryer performance and evidence of contamination at silencers or valve exhausts. If erratic motion appears after shutdowns, record ambient conditions and drain findings rather than immediately attributing the behaviour to worn cylinder seals. Separate pneumatic faults from mechanical resistance A sound pneumatic circuit cannot compensate for a binding mechanism. Inspect cylinder mounts, rod alignment, guides, linkages, stops and the driven load. Side loading can damage seals and bearings while also creating inconsistent motion. Cushion settings that are too restrictive can resemble a flow problem near the end of a stroke. Debris, thermal expansion or a changed workpiece can also increase resistance. Where the machine design and risk assessment allow it, compare actuator behaviour with the load safely removed or decoupled. If speed and repeatability return, the fault may be outside the cylinder. If the problem remains, continue checking pressure, flow and the actuator itself. Never disconnect a load unless stored energy, gravity and unexpected movement have been controlled. Change one condition at a time Good troubleshooting depends on preserving context. Record the asset, operating load, upstream and local pressure, extension and retraction time, valve state, flow-control settings, air-quality observations, nearby demand and the outcome of each change. Digital asset inspection software can help keep observations, photographs and corrective actions connected to the same equipment history. Likewise, well-designed manufacturing software can preserve process conditions and verification results instead of reducing the event to a closed work order. Change only one variable at a time whenever practical. Cleaning a silencer, adjusting a flow control and replacing a valve simultaneously may restore motion, but it prevents the team from learning which action mattered. After a correction, verify several cycles under normal load and during realistic plant demand. A single successful stroke is not proof that the root cause has been removed. Replace the cylinder only when the evidence points there Cylinder wear remains a legitimate failure mode. Internal leakage, damaged seals, scored surfaces, bent rods and worn bearings can all reduce force or create erratic movement. The point is not to exclude the cylinder, but to reach that conclusion after the circuit and mechanical load have been checked. A symptom-led process prevents unnecessary replacement and produces a more useful maintenance record. Measure pressure at the point of use, compare both directions, inspect supply and exhaust restrictions, assess air quality, check alignment and verify the repair under real operating conditions. When the full path is examined, technicians are more likely to correct the cause of inconsistent actuation instead of replacing the component at the end of it. *Palak Sheth is a Digital Marketing Specialist at Konverge Digital Solutions, She develops technical and educational content about inspection management, asset reliability, preventive maintenance, industrial troubleshooting and the practical use of operational data. A pneumatic circuit inspection should extend beyond the cylinder to the valve manifold, airpreparation components, tubing, flow controls and exhaust silencers. Restrictions or contamination in these components can produce unstable actuator speed. Image credit: AI-generated.
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