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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 such as 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 functional principle, two forces act:
The process pressure
It makes 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 (because of the large surface absorbing the pressure), whereas, at higher pressures, they have a piston with a small surface area.
The force of the preloaded spring
That 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 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 once the pressure increases, and the reset point is set accordingly once the pressure decreases.
What should be considered when selecting the setting range?
When selecting 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 instance, this is 60 bar (diaphragm) and 350 bar (piston).
The setting range is smaller compared to the overload safety. Because of this pressure spikes could be absorbed. That is important, for example, for idle-running protection in pumps. There, the machine pressure can be often greater 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, which offers high repeatability. A larger switching and overpressure range would consequently need a stronger diaphragm ? at the expense of repeatability.
Note
Further information on the PSM01 and PSM02 pressure switches can be found on the WIKA website. You want to buy pressure switches? In our WIKA online-shop you will discover a few of our standard designs. Should you have further questions, your contact will gladly help you.
Also read Spectacular
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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