The selection of different solenoid valves is huge. Just as difficult is occasionally the choice of which solenoid valve is the right one for a specific application. This must be selected based on several parameters, such as:
- Connection size
- Desired flow rate
- Desired switching pressure
- Media compatibility of the materials used
- Available power supply
- Price
- Personal preferences
1. How big is my connection?
Although it is possible to connect almost any small or large solenoid valve to an existing fitting, hose or pipe using adapters, this is not practical. If a pipe has a certain diameter, it is because a certain flow rate is to be achieved through the pipe. Here the solenoid valve should in no case become a "bottleneck" and not reduce the effective flow.
2. What is the desired flow rate?
Question 1 leads us directly to the 2nd question. Inside a solenoid valve, the medium is deflected a few times and passes through the valve seat, which can be regarded as a bottleneck in the valve. This deflection and the valve seat represent flow resistances for the medium. The flow coefficient must be used to estimate whether the valve allows the desired flow to be achieved. A prerequisite for this is, of course, that the inlet and outlet pipes from question 1 are also large enough.
3. How high is the desired switching pressure?
According to points 1 and 2, we are now trying to select a valve with as large a flow rate as possible, i.e. a valve with as large a nominal size as possible. However, this design is contradicted by the minimum switching pressure that the valve must be able to switch. This switching pressure usually decreases with increasing nominal diameters or better flow rates and it is therefore necessary to select a valve in such a way that both the desired switching pressure and the desired flow rate are achieved.
4. Media compatibility
The materials used in the solenoid valve must be matched to the medium used. There are a significant number of non-aggressive media which are compatible with most sealing materials such as EPDM or NBR and also do not attack metals such as brass or stainless steel. However, caution is required with certain media such as deionized water or even under certain circumstances such as steam at 150°C. Here, sealing materials must be used that have sufficient chemical and physical resistance to the medium. Consequences of an incorrectly selected gasket material may be that the gasket decomposes or swells. The same caution should be exercised with valve body materials used, such as the commonly used brass or stainless steel. While stainless steel is said to have largely good resistance to many chemicals, brass is used primarily in connection with non-aggressive media.
5. Voltage supply
Finally, the selected solenoid valve must match the voltage supply available for the application. In most cases, this is the European mains voltage of 230V 50Hz or a protective extra-low voltage of 24Vdc. The solenoid coils used, whose name usually has nothing to do with a permanent magnet but rather expresses that a magnetic field is generated by the current in the coil, must be matched to the voltage used.
6. Price
As a rule, one will choose the smallest possible and thus usually the cheapest valve that meets the requirements for connection size, flow rate and switching pressure.
7. Personal preferences
Often, personal preferences also contribute to the decision of the selected solenoid valve. Decisive factors can be, for example, the appearance of a stainless steel valve, the use of a rectifier junction box to avoid valve hum at 230Vac or the use of a higher quality sealing material to have reserves.
