Solenoid Valves

A solenoid valve is a device that controls the flow of a liquid or gas. Applying an electrical charge to a solenoid coil changes the state of a valve from open to closed, or vice versa, or shifts the flow path between various inlet, outlet and exhaust ports. This removes the need for an engineer to operate the valve manually. Solenoid valves function through electromagnetic operation and can be linked up to programming software and operated remotely, offering reliable operation and control of a process without relying on human interface. Click on the other boxes on this page for a quick crash-course on the basics of solenoid valves, their different designs, the solenoid valve functions available and their operations. If you require any further information, please contact the MGA Controls Ltd Sales Team on +44 (0)1704 898980 or sales@mgacontrols.co.uk

Direct acting solenoid valves work through a magnetic coil opening the valve in a direct action. As soon as the coil is electrically energised, a magnetic field is created which pulls the plunger up towards the centre of the coil. This opens the orifice so the medium can flow through. The media flows through a pipe and a small spring holds the plunger down to close the valve. Pilot operated valves work by a plunger opening up the pilot while pressure causes the valve to open and close. Pilot operated solenoid valves function with less electrical energy but need to maintain full power in order to remain open. Pilot operated valves function at a slower rate than direct acting solenoids. Solenoid valves are available in a wide range of configurations depending on the function they are required to perform, and the solenoid valve application that they are to be installed into. They are classified by abbreviating the number of valve ports and positions the valve has. For example, a 2/2 solenoid valve type has 2 ports, and 2 positions, where a 5/3 solenoid valve type has 5 ports and 3 positions.

A diaphragm type solenoid valve operates by a soft sealing diaphragm opening or closing against a valve seat. The media flows through the inlet port, over the seat and out of the downstream outlet port. In a Normally Closed Solenoid Valve type, the diaphragm remains closed until power is applied, at which point the diaphragm lifts and allows flow through the valve. Poppet type solenoid valves operate in a similar way to diaphragm type solenoid valves, but as opposed to a rubber diaphragm, they employ a disc or tapered plug to come into contact with a valve seat. They are most commonly supplied as direct-acting solenoid valves, and can be used in a wide range of solenoid valve applications. A Spool type solenoid valve is made up of a body with a cylindrical spool sitting inside a sleeve. The spool itself is full of many small holes which connect the valve ports and allow a pre-determined flow path through the valve. Once energised, the spool moves within the chamber, creating a different flow path through the valve.

Normally Closed – In its resting state, a normally closed solenoid valve type is shut, and does not allow flow. Once energised, the valve opens and allows the media to flow over the valve seat and out of the downstream outlet port. Normally Open – The opposite to a normally closed solenoid valve, normally open valves allow full flow through the valve with no power applied. To close the valve, you apply power to the solenoid coil which will stop the flow of media through the valve. Proportional – Sometimes applications require more flow control than simple on/off valves will allow. This is where proportional valves step in. They operate by taking an electrical input current, normally 4-20mA or 0-10v, and proportionally adjusting the valve position to regulate the flow. Sol/Spring (Monostable) or Sol/Sol (Bi-Stable) – Most commonly associated with Spool valves, these terms refer to the operation of the valve. A Sol/Spring valve uses the solenoid to actuate the valve to its second position, and allows the spring to return the valve to its resting state, where a Sol/Sol valve requires solenoid actuation in both directions.

Flow Rate – There is often a compromise to be reached between desired flow rate and available pipe size. When designing a system from scratch, ensure your solenoid valve has an orifice that is large enough to handle the flow rate required. Media Compatibility – Brass and plastic solenoid valve types are usually well suited for water applications. However, chemical cleaning products may be more aggressive and require stainless steel. Ensure your solenoid valve material (body and seal) is compatible with the media to guarantee longevity and optimum performance. Temperature – Different body materials and seals can handle different temperatures. It is always worth double checking your lowest and highest possible media and ambient temperatures to ensure the solenoid valve type that you choose is the best match for your application. If your solenoid valve application requires the temperature of the water to be higher, ensure the material you choose can sustain the heat. Operating Pressure – Solenoid Valves are available in a very wide range of operating pressures, from as low as 0.1 Bar up to 250 Bar and beyond. Ensure the solenoid valve type you choose is a correct match for your application.

Reliable Performance – Most gases contain impurities before processing which can cause problems when the valve is required to provide a tight shut-off. It is worth considering the fitment of a filter to ensure the gas is free of contaminants to maintain the optimum performance. Pressure Range – Operating pressures are extremely important. Some solenoid valve types require pressure assist and if the supply to the valve falls below the minimum pressure differential, the valve closes and shuts off heat. In some cases this causes a failure to operate. Consider the highest and lowest possible operating pressures before selecting your solenoid valve type. Low Power Consumption – Power is often in short supply and if this is the case you will want a solenoid valve to draw as little power as possible to operate. By choosing the correct power rating for your application, power consumption is minimised, contributing to energy and cost savings, and also a longer life cycle. Environment – When gas is present, it is quite common for the environment to be a hazardous area. Check the ATEX requirement of the site to ensure the valve is suitably protected. Failure to do this could cause a catastrophic explosion.