My solenoid valve isn’t closing when the coil is de-energized. What can cause this?

Usually we see the problem related to one of two situations. The first situation involves dirt. Solenoid valves have small internal ports leading to the actuation mechanism that can be clogged by foreign particles in the liquid. Remember, solenoid valves are not designed to handle liquids with solids. USABlueBook can supply other types of actuated valves that are suitable for “dirty” liquids and slurries.

The second situation involves improper differential pressure. Some solenoid valves’ actuators require a minimum differential pressure between the inlet and outlet ports. For example, if you are using a solenoid valve to fill an open tank from a pressurized water line, you obviously have plenty of differential pressure between the inlet and outlet side. However, if you were using a pump to supply water to a pressurized line (eg. a gas chlorine injector feed line), when the pump shuts off the back pressure at the discharge side of the valve may equal or actually exceed the supply pressure on the inlet side. In this example the valve will not close.

In this type of application select a solenoid valve designed for operation with “0” pressure differential. Even these will not work correctly if the line pressure on the discharge side of the valve exceeds that on the inlet side. For these applications you will need to install a check valve after the solenoid valve so that pressure on both sides of the valve will equalize.