A Complete Guide to Solenoid Valve Types and Usage
Also known as electromagnetic solenoid valves, solenoid valves are powered by electric current. Solenoid valves come with a built-in electric coil that has a ferromagnetic core (plunger). In its neutral position, the core or plunger keeps the valve closed or open. Normally closed solenoid valves open when the plunger is lifted by a magnetic field that is created when an electric current passes through the coil. Meanwhile, normally open solenoid valves close when the plunger is dropped due to the same process. Solenoid valves are used to open, close and distribute a variety of media including liquids, oils and gases.
Sirai and M&M solenoid valves
Sirai and M&M are two of the most well-known solenoid valve brands. Sirai solenoid valves have been on the market since the 1940s. They are commonly used to control the flow of air, water, gas, steam and other non-aggressive media. Sirai solenoid valves are either 2/2 or 3/2 and come as normally open or normally closed. Manufactured in Italy, M&M solenoid valves are both versatile and durable. They come in either ⅛-inch or 2-inch versions and feature a range of seal material options.
Water solenoid valves
Water solenoid valves are used to manage the flow of water at various temperatures, including clean and sewage water. Usually made from stainless steel, cast steel, brass or cast iron, water solenoid valves feature rubber seals so as not to pollute the flow. Water solenoid valves are commonly used in various applications and industries including dyeing, printing and the chemical and petroleum industries.
Brass solenoid valves
Brass solenoid valves are usually classified as normally closed, which means that they are only ever activated when fluid needs to be released. These valves open to release fluid when the coil is energised with an electrical current. Brass solenoid valves can be used to control the flow of water, oils and fuel.
Pilot operated solenoid valves
Also referred to as indirect acting solenoid valves, pilot operated solenoid valves utilise the difference in the energy of the pressurised gas or fluid over the inlet and outlet ports to open or close. To function, pilot operated solenoid valves need a minimum pressure differential of approximately 0.5 bar. Piloted solenoid valves are commonly used to manage flows in high-pressure piping systems.
Gas solenoid valves
Gas solenoid valves use an electrical current to manage the flow of gas in machines, boilers and industrial heaters. In particular, they can be used with gases such as air, helium, nitrogen, carbon dioxide, hydrogen and oxygen. The sealing material of many gas solenoid valves can handle temperatures of up to 500 degrees Celsius while the body of many such valves can withstand up to 100 Mpa of pressure.
Depending on their specific design, gas solenoid valves can be used in either low-pressure systems (domestic application) or high-pressure systems (industrial application). In domestic applications, gas solenoid valves are commonly used to supply gas to boilers and dryers. In industrial applications, they are often used to power pneumatic machinery.
Solenoid valves are used to control flow in various domestic and industrial applications, including:
- Washing machines, dryers and dishwashers.
- Air-conditioning systems.
- Irrigation systems and lawn sprinklers.
- Automatic locking systems.
- Refrigeration systems.
- Car washes and cleaning equipment.
Solenoid valves feature three main components. The first one is the body, which comes with two or three ports and valve seats. The second is an electrical coil, which is made from copper windings and closes and opens the valve when energised. Finally, the coil housing is the enclosure within which the coil moves. It is typically made from non-ferrous metal and sealed at one end.
Not all solenoid valves are the same. With this in mind, here are a few factors to take into account before purchasing a solenoid valve.
- What material is it made from? Solenoid valve housing material should depend on the temperature and specific properties of the media. Brass solenoid valves are normally used with neutral media. Meanwhile, stainless steel solenoid valves are temperature-, chemical- and pressure-resistant. Most seals are made from either Teflon or Viton.
- Do you need a solenoid valve with two or three ports?
- Do you need a solenoid valve that is normally open or normally closed? If the valve will be open most of the time, select a normally open solenoid valve. If it will be mostly closed, on the other hand, opt for a normally closed solenoid valve.
- What pressure do you need the solenoid valve to be able to withstand? Some solenoid valves can withstand up to 250 bar of pressure.
- Do you need a solenoid valve that is operated directly, indirectly or semi-directly?
- What response time do you need your solenoid valve to have? Response time refers to the time it takes for the valve to go from a fully open to a fully closed position and vice versa. Some solenoid valves come with an adjustable response time.
- Do you need a solenoid valve with a manual override? Manual overrides provide an additional level of safety in cases of power failures.
As their name suggests, two-way solenoid valves come with two ports and more specifically an inlet port and an outlet port. Also sometimes referred to as shut-off solenoids, two-way solenoid valves come in two types: normally open and normally closed. Meanwhile, three-way solenoid valves come with three ports, which can be used to divert flow (one inlet and two outlets) or mix flow (two inlets and one outlet). Three-way solenoid valves are usually used in more complex pipeline systems.
Used in applications that require flow, normally open solenoid valves are open when de-energised. The valve closes when an electric current is applied to the coil, creating an electromagnetic field that lowers the plunger against the seal. On the opposite end of the scale, normally closed solenoid valves are closed when de-energised. The valve opens when an electric current is applied to the coil, creating an electromagnetic field that lifts the plunger up. There are also bi-stable solenoid valves that switch after a momentary current supply. Bi-stable solenoid valves are also sometimes referred to as latching solenoid valves.
The main difference between these two types of solenoid valves is that direct-acting solenoid valves do not need a minimum operating pressure to function. They also do not require a pressure difference. The most common direct-acting solenoid valves are normally closed valves, which means that they do not let fluid through unless their built-in coil is electrically charged and creates a magnetic field that pulls the plunger upward. In the case of direct-acting solenoid valves that are normally open, the opposite happens. When the built-in coil is electrically charged and a magnetic field is created, the plunger is lowered to shut off the flow.
In pilot operated solenoid valves, or indirect-acting solenoid valves, the differential pressure of the flow causes the valve to either open or close. In order to operate, pilot operated solenoid valves need the differential pressure to be at least half a bar. Pilot operated solenoid valves are well-suited to high flow rates, temperatures and pressure ranges. They also consume less power than direct-acting solenoid valves.
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