Views: 20 Author: Site Editor Publish Time: 2025-06-02 Origin: Site
When it comes to solenoid valves, you may first think of it as a "switch" used to control the flow of liquid or gas. But have you noticed that some solenoid valves are marked "normally closed" and some are written "normally open"? Although there is only a difference of two words, their functions and usage scenarios are completely different! Today, let's talk about the difference between normally closed and normally open solenoid valves in a simple and easy-to-understand way.
In fact, "normally closed" and "normally open" refer to the default switch state of the solenoid valve when it is not powered on:
Normally closed solenoid valve
"Normal closed", as the name suggests, is the default closed state at ordinary times. Only when the power is on, the valve will open to allow the fluid to pass.
For example, if a normally closed solenoid valve is used in the gas pipeline at home, then when the power is off or a fault occurs, the gas flow will be automatically cut off, which can avoid danger.
Normally open solenoid valve
"Normal open" is just the opposite. It is usually open by default, and the valve will only be closed when the power is on.
Normally open solenoid valves are more suitable for scenarios where fluid flow needs to be maintained for a long time, such as some cooling systems or process flows that need to maintain a specific cycle.
The principles of normally closed and normally open solenoid valves are actually very simple. They both rely on electromagnetic coils to control the movement of the valve core to achieve switching. The difference lies in the coordination of springs and currents:
Normally closed type
When not powered, the force of the spring presses the valve core against the valve seat, and the fluid passage is blocked.
When the electromagnetic coil is powered, the magnetic field generated overcomes the pressure of the spring, the valve core moves up, and the fluid passage opens.
Normally open type
When not powered, the force of the spring pulls the valve core open, and the fluid can pass normally.
After power is turned on, the valve core moves downward under the action of the magnetic field, and the fluid passage is closed.
Therefore, whether it is normally closed or normally open, the core action of the solenoid valve is achieved by the "cooperation" of electromagnetic force and spring.
Which type of solenoid valve to choose depends mainly on the actual application requirements:
Application scenarios of normally closed type
Energy-saving requirements: Because it is closed most of the time, it is only powered on for a short time when needed, so it is more energy-saving.
Application scenarios of normally open type
Scenarios where fluid flow needs to be maintained for a long time: For example, cooling water circulation system, long-term power-off will waste energy, and normally open type is more suitable.
Scenarios to prevent power outages: For example, some process flows that require continuous access can still maintain fluid flow when power is off.
Avoid long-term power-on
Whether it is a normally closed or normally open solenoid valve, long-term power-on will cause the coil to heat up and may damage the solenoid valve. Therefore, in actual applications, some control devices can be used to reduce the continuous power-on time.
Voltage matching is very important
There are many voltage requirements for solenoid valves, such as AC220V, DC24V, etc. When selecting, be sure to confirm whether it is consistent with the system voltage to avoid burning the equipment.
Pay attention to the characteristics of the medium. If there are impurities or strong viscosity in the fluid, the valve core may not move flexibly. It is recommended to install a filter before the solenoid valve to extend its service life.
