Mechanical pressure switches in compact design ensure safe pressure monitoring in, for instance, 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 as the measuring element.
Staggering 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 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. Regarding low process pressures, mechanical pressure switches therefore include 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
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 must overcome. This is associated with a rise in the switch point?s value. The spring geometry is designed in line with the required switching range. In accordance with the functional principle of the mechanical pressure switch, the switch point is defined by the amount of spring preload. It really is set once the pressure increases, and the reset point is defined 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 example, this is 60 bar (diaphragm) and 350 bar (piston).
The setting range is smaller compared to the overload safety. Therefore pressure spikes could be absorbed. That is important, for instance, for idle-running protection in pumps. There, the system pressure can be many times greater than the switching value. Therefore, the PSM01 and PSM02 pressure switches in the piston version have a switching selection 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 expense of repeatability.
Note
More info on the PSM01 and PSM02 pressure switches are available on the WIKA website. You want to buy pressure switches? Inside our WIKA online-shop you will find some of our standard designs. In case you have further questions, your contact will gladly help you.
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