Mechanical pressure switches: What principle do they work on?

Mechanical pressure switches in compact design ensure safe pressure monitoring in, for instance, pumps, compressors and mobile working machines. Regardless of the application, they function in accordance with the principle of the preloaded spring, with a diaphragm or a piston as the measuring element.
Mechanical pressure switches like the PSM01 (see illustration) are constructed in accordance with the schematic diagram (left): electrical connection (1), adjustment screw (2), preloaded spring (3), switch contact (4), measuring element (5) and process connection (6). The model PSM01 and model PSM02 (with adjustable hysteresis) are compact switches. They will have a height of 50 mm (version with blade terminal) and spanner widths of 24 and 27.
With this particular functional principle, two forces act:
The process pressure
It creates the measuring part of the pressure switch react. The instruments are therefore designed in two ways. In the case of low process pressures, mechanical pressure switches therefore feature 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 must overcome. This is accompanied by a rise in the switch point?s value. The spring geometry is designed using the required switching range. Relative to the functional principle of the mechanical pressure switch, the switch point is defined by the degree of spring preload. It really is set when the pressure increases, and the reset point is set accordingly once the pressure decreases.
What must be considered when choosing the setting range?
When selecting the setting range, 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, this 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. That is important, for example, for idle-running protection in pumps. There, Definitive 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. Innocent of these two models can switch up to a maximum of 16 bar. The comparatively small range is explained by the particularly sensitive measuring element, that provides high repeatability. A more substantial switching 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 would like 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
How 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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