the temperature of the heat sink 2 as detected by the heat sensitive unit 9a other structural and functional details of the liquid cooling mechanism shown in fig1 are the same as those of the liquid cooling mechanism shown in fig1 the liquid cooling mechanism shown in fig1 operates in the same manner as the liquid cooling mechanism shown in fig1 since the heat sink 2 itself has a relatively large thermal capacity its temperature does rot drop immediately when the cooling liquid starts to flow through the cooling pipe 21 therefore the heat sensitive unit 9a mounted on the heat sink 2 is prevented from being too sensitive and hence the valve unit 9b is prevented from being opened and closed frequently fig1 schematically shows a liquid cooling mechanism for cooling two inverter devices in a water supply system having two pumps the water supply system shown in fig1 is a small size water supply facility for supplying water to a general multiple dwelling house or the like as shown in fig1 the water supply system has a pair of pumps 8 1 8 2 a pair of check valves 81 1 81 2 connected to the respective outlet ports of the pumps 8 1 8 2 a common outlet pipe 87 connected to the secondary sides of.