Abstract: A safety shut-off valve opening a flow path between the primary and secondary sides in case of usual operation, while shutting off the aforesaid path in response to an emergency shut-off signal, and particularly such safety shut-off valve cannot be reset unitl it is confirmed that there is no more leakage of gas on the secondary side of the shut-off valve after the shut-off action was once effected, thereby to attaining a very high safeness.

Abstract: A fan control system for cooling apparatus such as cooling tower in which water and air are brought into contact together. According to this system, the running speed of the fan is continuously and proportionally changed responsive to the temperature of the cooling water or the external atmospheric conditions, to substantially control the cooling capacity of the cooling apparatus. The control system consists of a main fan motor, an electronic adjustment circuit and a power transmission means consisting of a variable pitch diameter belt speed changing means and a constant pitch belt reduction device, whereby the speed changing ratio of the belt speed chaning means is continuously and proportionally changed depending upon the control signals from the adjustment circuit. Further, the adjustment circuit may have a soft-start control circuit.