Mechanical pressure switches in compact design ensure safe pressure monitoring in, for instance, pumps, compressors and mobile working machines. Whatever the application, they function relative to the principle of the preloaded spring, with a diaphragm or a piston as the measuring element.
Mechanical pressure switches such as the PSM01 (see illustration) are constructed in accordance with 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 makes the measuring component 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 (as a result of 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
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 associated with 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 degree of spring preload. It really is set once the pressure increases, and the reset point is defined accordingly when the pressure decreases.
What must be considered when selecting the setting range?
When choosing the setting range, it is crucial 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. This means that pressure spikes could be absorbed. That is important, for example, for idle-running protection in pumps. There, the system pressure can be many times higher than the switching value. Therefore, Bottom Line and PSM02 pressure switches in the piston version have a switching range of up to 320 bar. The diaphragm versions of these two models can switch up to a maximum of 16 bar. Controversial is explained by the particularly sensitive measuring element, which offers 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 would like to buy pressure switches? In our WIKA online-shop you will find some of our standard designs. Should 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