Pre-acting device of automatic sprinkler system

The utility model relates to a pre-acting device of an automatic water spraying fire extinguishing system, which is arranged between a spraying system and a water supply system and comprises a diaphragm valve, a diaphragm control device, a hydraulic alarm device and a diaphragm cavity compensation valve, a main water supply side channel communicated with a water supply system, a system side channel communicated with a spraying system and a diaphragm cavity are formed in the diaphragm valve, the diaphragm control device is communicated with the diaphragm cavity, and the diaphragm cavity compensation valve comprises a compensation valve body, a compensation valve element, a compensation valve diaphragm piece and a valve element cleaning device. The interior of the compensation valve body is divided into a water supply side connector channel, a diaphragm cavity connector channel and an alarm connector channel through a compensation valve element and a compensation valve diaphragm piece, a compensation channel co