These pneumatic troubleshooting charts cover many common problems

The following troubleshooting charts cover common problems with pneumatic equipment including actuators, filters, regulators, lubricators, air valves, directional control valves and air cylinders. These lists are intended as a starting point for troubleshooting since it is impossible to include all possibilities. If one of the following situations exists, work through the source and remedy lists as possible causes. Re-check operation after checking each source before trying another source.

Actuator Moving Abnormally Slow

Source/Symptom: Excessive air choke

Source/Symptom: Pressure too low

Filter / Regulator / Lubrication Unit

Source/Symptom: Air leak at regulator

A continuous air leak from the small vent hole in the regulator bonnet indicates a leaky main bonnet or diagram. Repair parts should be ordered at once and the regulator should be scheduled for repair. Overhaul kits with diaphragm and seals are available for most standard regulators.

IMPORTANT:
Replace a diaphragm or the seals as soon as possible after the leak is discovered. A complete failure of the diaphragm might apply full house pressure to the pneumatic system. This may cause some solenoid valves to shift by themselves, creating a safety hazard to personnel and equipment.

Source/Symptom: Pressure problems

If diaphragm is cracked or broken, a high velocity air leak at the vent hole will occur. Replace diaphragm.

Source/Symptom: Filter problems

Clean or replace the filter element regularly. When over-contaminated, the filter element will create a pressure drop which may affect system operation.

Drain condensate from the filter bowl before it rises above the baffle. Otherwise, air turbulence may pick up the water and carry it downstream into the pneumatic system. If condensate requires frequent draining, install an automatic drain.

Use filter elements with the appropriate rating to protect cylinder barrels and other smooth surfaces from harmful contaminants.

Directional Control Valve Not Changing Position

Source/Symptom: Coil not picking up

Source/Symptom: Valve spool stuck

Source/Symptom: Proportional valve not responding

Air Valves

Source/Symptom: Low voltage problems

Applying low voltage to an AC solenoid valve will cause the solenoid coil to draw high inrush current continuously and burn out, because there won't be enough magnetic force to seat the armature of the valve. Causes of low voltage include high resistance connections; and low voltage on the control transformer that powers the circuit.

Source/Symptom: Voltage transients

Solenoid burnout may be caused by high transient voltages that break down coil insulation, causing short circuits to ground. This problem is most common where solenoids are connected to voltage sources that supply motors and other inductive loads. Switching such loads on and off can cause very high voltage peaks that will be seen by all components in the circuit. The remedy is to isolate solenoid circuits. Use 120-volt control circuits and observe good grounding practices. Electrical filter networks may also be used.

Source/Symptom: AC hum

If the solenoid noise level is very high and occurs each time the solenoid is energized, operate the manual override to check to see that the armature is seating. If the noise decreases, it indicates incomplete solenoid motion. Clean all moving parts and check for correct voltage supply.

Extremely loud AC hum can be caused by a broken part within the solenoid. Replace the solenoid.

Source/Symptom: Valve spool stuck

The armature may be held unseated because a valve spool won't shift. The solenoid will draw high inrush current for too long a time and burn out.

A metal-to-metal spool-type valve may be varnished in place, or dirt may prevent the spool (and the solenoid armature) from shifting. Repair or replace.

Source/Symptom: Temperature problems

Solenoid failure can be expected when a valve is operated above its rated temperature. Insulation may fail, causing shorts to ground or shorts between turns of the coil. If ambient temperatures are too high, consider moving the valve or using a pilot-actuated valve with a remote pilot valve.

Air Cylinders

Source/Symptom: Drift

Piston seal leaks can cause a cylinder to drift from its normal position. To check the seal, pressurize one side of the piston and observe leakage from the opposite side. Virtually no air should leak past pistons equipped with soft seals. Replace seals as needed.

Other circuit leaks also can cause a cylinder to drift. Check for leaks through the directional control valve (internally and externally) and in connecting lines. Fix leaks as needed.

Source/Symptom: No movement

Source/Symptom: Erratic movement

Source/Symptom: Cylinder body seal leak

Source/Symptom: Rod gland seal leak

Source/Symptom: Contamination in circuit

For more information on fluids safety and troubleshooting, there are several Valmet articles available, or contact your Valmet representative.