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. Regardless of the application, they function in accordance with the principle of the preloaded spring, with a diaphragm or perhaps a piston as the measuring element.
Mechanical pressure switches like 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). The model PSM01 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 particular 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 feature a diaphragm (due to the large surface area absorbing the pressure), whereas, at higher pressures, they will 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 associated with an increase in the switch point?s value. The spring geometry was created based on 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. Humility is set once the pressure increases, and the reset point is set accordingly once the pressure decreases.
What should be considered when choosing the setting range?
When choosing the setting range, it is crucial for the user to consider the maximum system pressure to that your pressure switch is subjected. Regarding the WIKA compact instruments, PSM01 and PSM02 (with adjustable hysteresis), for example, this is 60 bar (diaphragm) and 350 bar (piston).
The setting range is smaller than the overload safety. Because of this pressure spikes can be absorbed. This is important, for instance, for idle-running protection in pumps. There, the system pressure can be often 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, that provides high repeatability. A more substantial switching and overpressure range would consequently require 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 discover a few of our standard designs. In case you have further questions, your contact will gladly assist you to.
Also read our posts
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Mechanical vs. electronic pressure switches: Functionality

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