Troubleshooting Pneumatic Systems: Leaking Manifold Valves

Pneumatic Maintenance Situation

A machine operator running an automated assembly machine notices air leaking from the exhaust port of a 5-station valve manifold and notifies the maintenance team.

A maintenance technician does confirm that compressed air is constantly leaking from the one of the exhaust ports of the valve manifold.

He shuts off the main air going to the machine and replaces one solenoid valve at a time trying to find the defective solenoid valve.

After turning the main air on/off each time he replaces a valve, the valve manifold is still leaking air from the exhaust port after replacing all 5 solenoid valves.

So why is the valve manifold still leaking from the exhaust port???

Pneumatic Air Leak Detection

99.9% of the time, if air is leaking from an individual air valve or air valve manifold, it is because you have a bad seal on an air cylinder or rotary actuator.

So, in the example above, with a worn or damaged piston seal (#1) the compressed air that is holding the air cylinder in the retracted position is leaking pass the piston seal into the rear part of the air cylinder (#2) though the air valve and out the exhaust port EA (#3).

The best way to figure out if the valve is bad or you do have a bad piston seal is to use a pair of needle nose pliers and pinch off the tubing that is going to each of your air cylinders. This is especially true if you have a large valve manifold with several pneumatic actuators on the machine. Start at one end the manifold and go to each station and start pinching off the tubing. Once the air leak stops, then you found the leaking air cylinder.

Written by: Ralph Quarto, Engineer, Numatic Engineering

If you have questions regarding this article or questions about your pneumatic application, please e-mail me at [email protected]

Congratulations to August’s Quiz Contest Winner: Mike McClean

August’s quiz was a contest asking readers why the valve manifold was still leaking from the exhaust port? Mike McClean answered, “Likely one of the attached cylinders has blow-by on the piston seal.” Mike won a $25 Amazon gift card. Congratulations!

September’s quiz contest asks readers how to prevent hard stops when a cylinder travels to a home position. Please join our conversations and provide your answers. Next month’s article will share the best-practice for pneumatic system design and the quiz contest’s winner. Good luck!