Pressure data in all FEMA documents refers to relative pressure. That is to say, it concerns pressure differentials relative to atmospheric pressure. Overpressures have a positive sign, vacuums a negative sign. Permissible working pressure (maximum permissible pressure) The maximum working pressure is defined as the upper limit at which the operation, switching reliability and water tightness are in no way impaired (for values see Product summary). Bursting pressure (test pressure) Type-tested products undergo a pressure test certified by TÜV affirming that the bursting pressure reaches at least the values mentioned in the Product summary. During the pressure tests the measuring bellows are permanently deformed, but the pressurized parts do not leak or burst. The bursting pressure is usually a multiple of the permissible working pressure. Setting range Pressure range in which the cutoff pressure can be set with the setting spindle. Pressure units

Pressure data for a pressure switchbased on the example of DWR625: Setting range: 0.5-6 bar Perm. working pressure: 20 bar Bursting pressure: >100 bar

Switching differential The switching differential (hysteresis) is the difference in pressure between the switching point (SP) and the reset point (RSP) of a pressure switch. Switching differential tolerances occur due to tolerances in the microswitches, springs and pressure bellows. Therefore the data in the product summaries always refers to average values. In the case of limiter functions the switching differential has no significance, as one is only interested in the switching point at which cutoff occurs, not the reset point. For a controller function, i. e. in the case of pressure switches used to switch a burner, pump etc. on and off, a pressure switch with an adjustable switching differential should be chosen. The switching frequency of the burner or pump can be varied by changing the switching differentia