預作用系統在伺應狀態時系統側管網充以一定壓力的氣體，其主要功能是監測管網的密封性是否完好。控制系統一般由電磁閥、控制柜和火災報警系統組成。消防控制室接到探測器發出的火災信號后，通過控制柜打開電磁閥，從而打開預作用系統，壓力水充滿管網，同時發出報警信號，待火災進一步發展使噴頭爆破時，才噴水滅火，如果探測器發生誤報，預作用系統開啟，系統側管網充水，但沒有噴頭爆破，所以不會噴水，從而避免了水漬損失。在控制管路上設有緊急手動開關，用于聯動失效時，手啟動預作用系統。監測氣壓為 0.03-0.05MPa。當系統氣壓低于 0.02MPa時，由壓力開關發出故障報警信號，提醒維修管網。

本預作用裝置的配置，是在雨淋閥組件上安裝同一通徑的止回閥，在止回閥應預注一定量的底水，用于封閉管網，保持氣壓。

Pre-action system filling with certain pressure gas in the system side pipe network in ready condition mainly function is to supervise whether pipe network is air tightness or not. The controlling system is generally made up by magnetic valve, control cabinet and fire alarm system. When the fire control room receives fire signal sent by the detector, the magnetic valve will be open through the control cabinet, hence starts the pre-action system, fills the pipe network with pressure water and sends alerting signal, and then sprays water until the fire explode the sprayer. In case of wrongly alarm of the detector, the pre-action system open and fill the pipe network with pressure water, as long as there is no explosion of sprayer, the water will be saved and thus avoid loss of water logging. Emergency hand switch is equipped on the tube of control valve to start manual pre-action system in case failure of linkage. The monitoring pressure is 0.03-0.05MPa. When the system pressure is lower than 0.02Mpa, the pressure switch will send failure alarm signal to warn that the pipe network need to maintenance. The pre-action valve installation is to install a same diameter check valve on the assembly component of deluge alarm valve, and a certain amount of water shall be pre-grout to close the pipe network and keep pressure.