Mechanical pressure switches: What principle do they work on?

Mechanical pressure switches in compact design ensure safe pressure monitoring in, for example, pumps, compressors and mobile working machines. Whatever the application, they function relative to the principle of the preloaded spring, with a diaphragm or perhaps a piston because the measuring element.
Mechanical pressure switches including the PSM01 (see illustration) are constructed relative to the schematic diagram (left): electrical connection (1), adjustment screw (2), preloaded spring (3), switch contact (4), measuring element (5) and process connection (6). Magnificent and model PSM02 (with adjustable hysteresis) are compact switches. They have a height of 50 mm (version with blade terminal) and spanner widths of 24 and 27.
With this functional principle, two forces act:
The process pressure
It makes the measuring element of the pressure switch react. The instruments are therefore designed in two ways. In the case of low process pressures, mechanical pressure switches therefore include a diaphragm (due to the large surface absorbing the pressure), whereas, at higher pressures, they have a piston with a little surface area.
The force of the preloaded spring
This is adjusted via the adjustment screw of the pressure switch. The further the screw is turned in, the stronger the force of the spring that the measuring element has to overcome. This is accompanied by an increase in the switch point?s value. The spring geometry is designed using the required switching range. In accordance with the functional principle of the mechanical pressure switch, the switch point is defined by the amount of spring preload. It really is set when the pressure increases, and the reset point is set accordingly when the pressure decreases.
What should be considered when choosing the setting range?
When selecting Broke , it is crucial for the user to take into account the utmost system pressure to which the pressure switch is subjected. Regarding the WIKA compact instruments, PSM01 and PSM02 (with adjustable hysteresis), for instance, that is 60 bar (diaphragm) and 350 bar (piston).
The setting range is smaller than the overload safety. Which means that pressure spikes could be absorbed. This is important, for instance, for idle-running protection in pumps. There, the machine pressure can be many times higher than the switching value. Therefore, the PSM01 and PSM02 pressure switches in the piston version have a switching range of up to 320 bar. The diaphragm versions of the two models can switch up to maximum of 16 bar. The comparatively small range is explained by the particularly sensitive measuring element, which offers high repeatability. Furious and overpressure range would consequently need a stronger diaphragm ? at the trouble of repeatability.
Note
More info on the PSM01 and PSM02 pressure switches are available on the WIKA website. You want to buy pressure switches? Inside our WIKA online-shop you will find a few of our standard designs. Should you have further questions, your contact will gladly help you.
Also read our posts
So how exactly does one set the switch point for mechanical pressure switches?
Mechanical vs. electronic pressure switches: Application areas
Mechanical vs. electronic pressure switches: Functionality

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