How a solenoid coil works

Posted by John Hamilton

images 1How a solenoid coil works

A solenoid is a coil of wire which wraps around a piston type of device. When a solenoid is energized, a magnetic field is created when current is applied and the piston (plunger) of the mechanism lifts off the port in the valve assembly- which results in the valve opening.

When the power is shut off to the solenoid the electromagnetic field dissipates and the plunger assembly seats back down over the port and the valve shuts down.

why solenoid coils fail

Like all electrical coils, solenoids will heat up when power is applied to them, and the water which is traveling through the valve assembly will actually keep them cool.

If power is applied to a solenoid repeatedly over time without a cooling source, then there is a higher chance that the coil of the solenoid could burn out over time.

When doing routine maintenance on irrigation valves, you may have run across a electrical solenoid where you see small bubbles on top of the solenoid, or you may have seen black marks on the solenoid wires. These black marks will show up on wires colored white, green, blue, or whatever other color the wires may be. It may be difficult to see on black wire. These bubbles are a prime indicator that the solenoid is generating excessive heat, and these marks are actually heat / burn marks. This is a pre-cursor of a solenoid which may fail in the near future, and one which should be changed out.

Another reason solenoids will fail is if they are cycled on and off repeatedly over time. The initial charge when electricity is applied generates the most amount of heat; therefore, if a solenoid is always be asked to turn on and off quickly, then the solenoid does not have a chance to cool down.

Why this occurs

We see this occurring on valves which have been turned off hydraulically; yet, not electrically back at the controller or central computer. As noted in the first paragraph, irrigation solenoids are cooled by the water flowing through the valve assembly when they are on. If water is turned off and the solenoid continues to operate over time because the program was not modified, then the solenoid heats up to the point of causing damage. The heat which builds up is not excessive enough to cause a fire; yet, over time the solenoid will essentially overheat and fail.

For more information on Electrical Troubleshooting contact Golf Irrigation Consultants: 415-342-1030