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 relative to the principle of the preloaded spring, with a diaphragm or perhaps a piston because 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 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 feature a diaphragm (because of 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 accompanied by an increase in the switch point?s value. The spring geometry was created 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 is set when the pressure increases, and the reset point is set accordingly once the pressure decreases.
What must be considered when selecting the setting range?
When selecting the setting range, it is important for the user to consider the maximum 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, this is 60 bar (diaphragm) and 350 bar (piston).
The setting range is smaller compared to the overload safety. This means that 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 selection 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 more substantial switching and overpressure range would consequently need a stronger diaphragm ? at the expense of repeatability.
Note
Never 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 some of our standard designs. Should you have further questions, your contact will gladly assist you to.
Also read our posts
So how exactly does one set the switch point for mechanical pressure switches?
Mechanical vs. electronic pressure switches: Application areas
Mechanical vs. electronic pressure switches: Functionality

Leave a Comment