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 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). ไดอะแฟรม 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 will have a piston with a small 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 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. It really is set when the pressure increases, and the reset point is defined accordingly when the pressure decreases.
What should be considered when choosing the setting range?
When selecting the setting range, it is necessary 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 compared to the overload safety. Which means that pressure spikes can be absorbed. That 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 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 require a stronger diaphragm ? at the trouble of repeatability.
Note
Further information on the PSM01 and PSM02 pressure switches are available on the WIKA website. You would like to buy pressure switches? In our WIKA online-shop you will discover some of our standard designs. In case you have further questions, your contact will gladly assist you to.
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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