Normally Open vs. Normally Closed Solenoid Valves

Solenoid valve has strong controllability, long service life with strong materials and reliable design. It is widely used in the automatic control systems including textile, printing and dyeing, food processing, medical equipment, petrochemical, metallurgy and so on.

According to the working state, the solenoid valve products can be divided into normally open solenoid valves and normally closed solenoid valves. There is also a kind of solenoid valve, namely, self-retaining solenoid valves, also called normally open normally closed solenoid valves.

Working principle of normally open and normally closed solenoid valves

1. Normally open solenoid valve

When the coil is de-energized, the solenoid valve is opened; when the coil is energized, the solenoid valve is closed.

2. Normally closed solenoid valve

When the coil is de-energized, the solenoid valve is closed; when the coil is energized, the solenoid valve is opened.

Selection of normally open and normally closed solenoid valves

The normally closed type or the normally open type can be chosen according to the duration of the continuous working time.

1. The normally closed solenoid valve is selected when the solenoid valve needs to be closed for a long time, and the closing time is longer than the opening time, and the continuous opening time is not very long.

2. A long time of opening and closing are both needed, thus self-retaining solenoid valves should be chosen.

3. When the solenoid valve needs to be opened for a long time, and the opening time is longer than the closing time, and the continuous opening time is not very long, you can choose the normally open type.

4. For gas alarm system, it is necessary to choose the normally open gas emergency cut-off solenoid valve with manual opening.

5. However, in some conditions that is applied to safety protection, such as furnace and kiln fire monitoring, the normally open solenoid valve cannot be selected.