FAQs about solenoid valves

Frequently Asked Questions about Solenoid Valves

Frequently Asked Questions about Solenoid Valves


1. What is the working principle of an On/Off solenoid valve?

On/Off Solenoid valves are electromagnetic valves that control flow rates of liquids or gases. On/Off solenoid valves are either fully open or closed; there is no midway point these are not proportional control solenoid valves. When the coil is activated a magnet force opens the valve against a spring. When the coil is de-energised the spring closes the valve.


2. Why is a solenoid valve used?

Solenoids are used to automate liquid or gas flow circuits by opening or closing valves by the application of a magnetic current generated when the solenoid coil is energised (receives an electric current). Corresponding to the existing mains voltages, they are designed as DC or AC coils. We customise our valves to fit your applications, ensuring an optimal solution – whatever your needs. Whether you need a single valve, valve blocks or customised solutions, our entire product line is designed to ensure controlled handling of liquids and gases.


3. What is the difference between direct acting and pilot operated solenoid valves?

With direct acting solenoid valves the power generated in the coil/spring is sufficient to open the valve on its own. Direct acting valves can work from zero pressure. Whereas with servo-assisted solenoid valves a main valve is controlled by a solenoid-operated pilot valve with smaller flow cross-sections and lower electrical control power. Servo-assisted solenoid valves require assistance from the media flowing through the valve in order to fully open and close, direct acting valves do not. There is sufficient force generated by the coil to open the valve at zero pressure.


4. What different solenoid valve types are available?

There are two main types of solenoid valve, which are direct acting or servo-assisted. Solenoid valves can be further subdivided by their circuit function, in other words how many ports they have and in what position they operate. For example, a 2 port 2 position valve (2/2 way) can either be normally open (energise to close) or normally closed (energise to open). View our solenoid selection chart for more information.


5. What is a pneumatic solenoid valve?

A pneumatic solenoid valve is a valve that has been designed for use on gas circuits (usually compressed air) and are often used to actuate larger process valves or pneumatic cylinders. They are often servo-assisted valves which require a minimum pressure differential to work. Pneumatic valves can operate on their own, or be grouped together on a manifold with common exhaust and pressure supply ports.


6. How to control a solenoid valve?

In an on/off 2/2 way normally closed solenoid valve once the coil is energised the plunger/armature moves against a spring  by the creation of a magnetic force. If the magnetic force is removed, by cutting the electric current to the coil or de-energising it, the force created by the compressed spring takes over and moves the plunger/armature back into its original position.


7. How to select a solenoid valve?

Solenoid valves are selected based on the following criteria:

Media – what is flowing through the valve?

Pressure – what pressure is the media at (Min/max)?

What temperature is the media at (Min/Max)?

What is the ambient temperature?

What circuit function is required – what do you want the valve to do?

What flow rate is required through the valve?

What body and seal combination is required (based on the chemical resistance of these materials to the media passing through the valve)?

What supply voltage is required? Power consumption?


8. My solenoid valve won’t open/close

This sort of failure can usually be attributed to one of the following causes:

If it is a servo-assisted valve, the system pressure differential is too low to open or close the valve. Please check the system pressure to ensure there is a minimum pressure differential of between 0.5 to 1 bar across the valve.

If the system pressure is okay, but the servo-assisted valve will still not open, please check that the bleed hole in the diaphragm has not become blocked by debris in the fluid.

It is good practice to ensure debris is kept out of the valves by fitting a dirt filter before the valve inlet. This needs to be <500µm in size to trap particulate.

If the valve is installed on new pipework, this should be checked prior to installation to make sure it is clean and debris free.

Check you are applying the correct voltage to the valve.

Check that the device is not damaged.

If it is a direct acting valve, check that there is no particulate in the valve core which is stopping the plunger from moving.

Check that the system pressure is within specification for the valve.


9. What is the average solenoid valve life expectancy?

As each application is different and unique, it is impossible to give an average lifespan for our general purpose solenoid valves. How long the valve will operate for depends entirely on how it is used and under what conditions. We do however provide service kits which can be used to extend the operational life of the valve.

For our micro fluidic valves, we can give an indication of the operational life by testing the valves under laboratory conditions with Water at 20°C and 1 bar pressure.


10. Where to buy solenoid valves?

The best place to buy solenoid valves is: Solenoid Select - part of Valves Online

Phone: 01822 855600