Pressure limiter
The pressure limiter is a safety-relevant piece of equipment to protect system parts from impermissible pressures . According to EN 50156-1, the limiter is a signal transmitter that interrupts the power supply when a fixed limit value is reached ... and remains in this state until it is manually reset.
The component is used to initiate electrical switching functions when the permissible pressure of system parts has been exceeded or fallen below (maximum pressure / minimum pressure limiter). In contrast to the pressure monitor, the switching contacts of the pressure limiter are locked so that the system does not start up again automatically when a permissible pressure is reached again. The pressure limiter must be unlocked by manual intervention either on the device itself or by an electrical circuit . The pressure limiter is particularly required when it is to be expected that the occurrence of an inadmissible system condition is the result of a system malfunction and that the operator's intervention is required.
The pressure limiter is required in the technical regulations for certain pressure equipment systems, e.g. B. on steam boiler systems , refrigeration systems or chemical reactors in which exothermic reactions can occur. Typical switching functions of pressure limiters are: closing valves , switching off pumps or compressors . As far as the limit value of the pressure limiter z. B. can be adjusted by a spindle, the setting must be secured against unauthorized change, z. B. by sealing or sealing wax .
If pressure limiters are installed in systems that are subject to the Pressure Equipment Directive , they are considered equipment parts with a safety function and must be certified according to this EC Directive.
Pressure limiters are electromechanical components. The pressure to be monitored acts on a membrane which presses against an adjustable spring force. When the set limit value is exceeded, the switch contacts are opened via a ratchet mechanism. When the pressure is within the permissible range again, the latch can be unlocked using the reset button. However, the hysteresis of the limiter must be taken into account, ie the pressure at which the limiter can be reset is lower than the switching pressure.