The structure and the realization of solenoid valves allow a variety of different possibilities. For example, they can be divided into the following categories:
- Type of operation: direct operated, pilot operated, forced operated, coaxial valve
- Function: NC, NO, latching
- Material: brass, stainless steel, plastic
- Seal: NBR, FPM, EPDM, FFKM, PUR, PTFE
- Ways: 2/2-way, 3/2-way
- Connections: connections in the body, connection on the guide tube
- Flow redirection: ordinary solenoid valve, in-line valve
- Seal: by membrane, seal carrier, piston
- Media separated valves
This variety of different designs of solenoid valves results from the different applications in which they are used. The list below shows which properties of a solenoid valve are good or bad for the respective application. Not every property listed above will be discussed.
High pressure valves are usually direct acting valves or pilot operated valves with pistons. In the latter case, PTFE is often used as a sealing material, which also has excellent media resistance. Small valves up to G1/4 are often made of brass or stainless steel. Larger valves from G1/2 are always made of stainless steel.
Valves for large flow rates require large nominal widths, which in most cases can no longer be switched by directly controlled valves. Pilot operated valves are therefore used for pressures from approx. 0.5 bar, or force pilot operated valves with powerful solenoid coils for pressures from approx. 0 bar.
A special type here are the so-called coaxial valves, which can switch large nominal widths and high pressures at the same time by means of a pressure relief and do not require a minimum pressure.
There are a number of highly resistant sealing materials for handling aggressive media that have sufficient resistance to the medium used. When it comes to the material for the valve body, stainless steel usually has a higher resistance than brass. However, the individual types of stainless steel also differ significantly in terms of durability. The so-called V4A steels such as 1.4404 are more durable than V2A steels such as 1.4305. When dealing with particularly aggressive media, it may also be necessary to use media-separated valves with valve bodies made of plastic or PTFE, whereby the medium cannot flow into the area of the plunger.
Dead space free valves
In some applications it can make sense that no medium remains inside the valve. Such valves are referred to as free of dead space and are practically designed in form of an inline valve, for example.
Large flow at low pressures
In applications that require high flow rates at low pressures, such as emptying tanks, the valve must be fully open. Directly controlled valves are better suited here than forced-controlled valves.
Hum-free solenoid valves
AC valves can produce a 100Hz hum that can be annoying in certain applications. This mainly affects NO valves or 3/2-way valves. To avoid this, a DC coil can be used instead of the AC coil or a DC coil can be supplied from the AC network with a rectifier plug instead of the AC coil.
Energy-saving solenoid valves
- There are several ways to limit the energy consumption of solenoid valves.
- In case of pilot-operated valves, a weak solenoid coil is often sufficient to be able to switch large pressure differences.
- DC valves can be equipped with a power reduction plug, which significantly reduces the power consumed by the solenoid valve.
- Large, low-power coils can generate the same electromagnetic force as smaller coils with greater electrical power.
- Latching valves use a permanent magnet and spring to hold the valve in the last state it was in even though there is no voltage present. This leads to significant power savings, especially in case of long duty cycles.
While 2/2-way valves can only release or stop the flow, 3/2-way valves allow a greater range of functions:
- A 3/2-way NC function or NO function leads a medium to the pressure outlet and can relieve the pressure on the connected consumer in the other switching position.
- A mix function can be used to combine the media from two ports into one output.
- A distribution function reverses this principle and distributes the medium from one input to two outputs.