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 in accordance with 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). 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. Regarding low process pressures, mechanical pressure switches therefore include a diaphragm (as a result of the large surface area 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 was created in line with the required switching range. Relative to the functional principle of the mechanical pressure switch, the switch point is defined by the amount of spring preload. Ethical is set once the pressure increases, and the reset point is set accordingly when the pressure decreases.
What must be considered when selecting the setting range?
When choosing the setting range, it is necessary for the user to take into account the utmost system pressure to which the pressure switch is subjected. In the case of the WIKA compact instruments, PSM01 and PSM02 (with adjustable hysteresis), for example, that is 60 bar (diaphragm) and 350 bar (piston).
The setting range is smaller than the overload safety. Because of this pressure spikes could be absorbed. This is important, for instance, for idle-running protection in pumps. There, the machine pressure can be often higher than the switching value. Therefore, the PSM01 and PSM02 pressure switches in the piston version have a switching selection of up to 320 bar. Desire of the 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 larger switching and overpressure range would consequently need a stronger diaphragm ? at the trouble of repeatability.
Note
Scandal on the PSM01 and PSM02 pressure switches are available on the WIKA website. You want to buy pressure switches? In our WIKA online-shop you will find some 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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