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

Possible Problem	Recommended Action
Flow control valve incorrectly adjusted	Readjust the valve.
Plugged air silencer	Replace or clean silencer.
Air leak or squeezed tube	Repair air leak or tube.
Plugged filter	Replace air filter.
Damaged cylinder or seal	Replace cylinder or seal.

 

Source/Symptom: Pressure too low

Possible Problem	Recommended Action
Damaged or incorrectly adjusted pressure regulator valve	Replace regulator or readjust rating as shown in drawing.
Plugged filter	Replace filter.
System leaks	Fix leaks.
Directional or other valve open due to dirt or failed pilot circuit	Locate damaged part and clean or replace it.
Cylinder pipe, piston or seal damaged	Repair or renew damaged parts.

 

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

Possible Problem	Recommended Action
Electric failure	Fix electric failure and check mechanical spool movement.

 

Source/Symptom: Valve spool stuck

Possible Problem	Recommended Action
Impurities between spool and sleeve	Replace valve.
Valve pilot not working	Replace or clean piloting part.

 

Source/Symptom: Proportional valve not responding

Possible Problem	Recommended Action
Valve not receiving set value from program	Locate and fix electric failure.
Set value received but valve not responding	Replace the proportional valve.

 

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

Possible Problem	Recommended Action
Pressure too low	Check pressure at cylinder to make sure it meets circuit requirements.
Piston seal leak	Operate valve to cycle cylinder. Observe fluid flow at valve exhaust ports at end of cylinder stroke. Replace piston seals if flow is excessive.
Scored cylinder bore	Replace necessary parts. Eliminate contaminants from air supply.

 

Source/Symptom: Erratic movement

Possible Problem	Recommended Action
Load misalignment	Re-align cylinder and load.
Large difference between static and dynamic friction	Install flow control valves to provide back pressure to control stroke.

 

Source/Symptom: Cylinder body seal leak

Possible Problem	Recommended Action
Loose tie rod	Repair or replace.
Excessive pressure	Repair or replace.
Pinched or extruded seal	Repair or replace.
Seal deterioration - soft, gummy	Repair or replace.
Seal deterioration - hard, brittle. Usually due to temperature extremes.	Repair or replace.
Seal deterioration - wear	Repair or replace.

 

Source/Symptom: Rod gland seal leak

Possible Problem	Recommended Action
Torn or worn seal	Examine piston rod for dents, gouges or score marks. Repair or replace. Check gland bearing for wear. Repair or replace.
Pinched or extruded seal	Replace gland seal.
Seal deterioration - soft, gummy	Check compatibility of seals with lubricant. Replace with new seals.
Seal deterioration - hard, brittle. Usually due to temperature extremes.	Replace seals and shield cylinder from temperature extremes.
Seal deterioration - wear	Replace seals.

 

Source/Symptom: Contamination in circuit

Possible Problem	Recommended Action
Sealing compound inside fittings	Protect fittings during storage. Follow proper sealing procedures. Disconnect cylinder from circuit and attempt to clear debris from lines by aggressive air blast.
Improperly filtered feed pipes	Evaluate circuit design, consider adding pre-filters.
Burrs inside piping components	Components and/or piping not protected during repairs and/or storage. Disconnect cylinder from pipes and remove burrs. Clear remaining debris from lines with aggressive air blast.
Seals extruding from excessive pressure	Troubleshoot cause for excessive pressure and make changes to prevent. Reseat seals if possible, otherwise clean and reseal.
Generally excessive dirt in circuit	Wipers or boots not used on cylinders where needed. Evaluate circuit design, consider adding wipers or boots to cylinders.

 

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