Abstract: A pipe connecting the equipment to be protected with a vessel is locally divided in two paths, a pump and a one-way valve being mounted in one path and an electro-magnetic valve in the other path. Pump and electric valve are controlled by a contact manometer so to fill or to empty the vessel depending on the pressure in the equipment.The liquid body in the vessel moves a diaphragm between a position above the pipe connection but below a discharge opening and a position above this opening, in which latter position liquid is discharged through a siphon provided on the opening.The diaphragm divides the vessel in two spaces and is the bottom of a bag secured to the vessel.A float in a container connected to the vessel opens a feeding valve when the liquid level in this vessel is beneath a determined value.