Collaborative Troubleshooting

It's a fairly common story around electro-hydraulic systems. A cylinder or motor is not moving when it should. The millwright and the electrician both arrive at the directional valve stand.

Electrical vs. Mechanical

Is the problem an electrical fault, or is it a mechanical issue? In the case of a basic, solenoid operated, on-off type of directional spool valve, the diagnostic logic is not too complex.

Basic Mechanical Binding

Operate the valve solenoid. There may be more than one solenoid, so test them one at a time. If cylinder/motor load pressure registers on a gauge installed in the 'A' or 'B' work port lines, and yet the motor does not move at all, then most likely there is mechanical binding occurring at the motion points on the machine. This is a basic mechanical fault. It is not even a hydraulic fault.

If the 'A' or 'B' work port lines that connect to the cylinder or motor are of the flexible hose type, then test gauges may not even be necessary. If the hoses flex as the valve is operated, this is a sign that the valve spool has moved when the solenoid is active.

Stuck Spool - Contamination

If the hoses didn't flex or register a pressure when the solenoid was operated, then valve testing is next. If the valve has a mechanical override button, it can probably be operated with a push from a small screwdriver blade or hex key. If the cylinder or motor is now moving, then the valve is working mechanically.

If the spool was stuck due to contamination, then the override action may have loosened the jammed components. Try the electrical operation of the valve once again. If the valve is now working and the cylinder or motor is moving, then the problem is solved, except for the contamination in the system.

Electrical Fault

If the mechanical override of the valve didn't result in restored function for the electrical signalling as well, then more diagnostic work is needed. Remove the connector from the valve and test the cable side of the connection with a voltmeter while operating the switch to the valve.

If the voltage is present at the end of the cable, the next step is a solenoid test. The solenoid winding may be open (burned out). Use an ohmmeter to test the solenoid winding. If the ohmmeter registers a very high resistance or an out-of-limits (OL) reading, then a new solenoid is needed.

This diagnostic process is usually sufficient to solve a problem for a simple valve-to-actuator application.

About the author: Carl Dyke resides in Central Alberta, Canada and collaborates daily with the team of very passionate individuals who create & deliver the products and services of CD Industrial Group Inc.

Carl grew up looking after the machinery and equipment used in timber and lumber processing. After some early career years spent in public education, a unique enterprise was born. Carl and team spend their days demystifying complex machinery, creating interactive art and software that aids learning, and conducting instructor-led maintenance training and consulting, globally, for a wide range of heavy industries.