Abstract: The invention comprises an improved pressure transfer module having, in one embodiment, two double-diaphragm pumps each having its diaphragms connected to one another by a respective drive shaft for reciprocating motion. Spool valve assemblies are mounted directly on the connecting shafts of each pump and arranged to maintain the operation of the two diaphragms of the pumps 90.degree. out of phase in that each such assembly constitutes pressurized water control valves for the other pump. The two pumps are mounted with the drive shafts at 90.degree. to one another, and arranged to pump in sequence so that a complete pumping cycle comprises four pumping strokes, one every 90.degree.. To insure reversal of motion of the shafts in proper phase, the invention includes either two, meshed square cams and cam surfaces formed on respective shafts connecting the pumping surfaces, or a floating crankshaft with each end pivoted in one of the connecting shafts.

Abstract: A water heater (10) has a pressure-transfer module (20) interposed between an external pressurized-water circuit and the water inside the water-heater vessel (12) so that the water is at atmospheric pressure and can thus have a free upper surface. A shut-off valve in the inlet (14) to the pressure-transfer module (20) is controlled in accordance with the water level as detected by a float (74). If the water level falls below a predetermined minimum or exceeds a predetermined maximum, the shut-off valve closes so as to prevent further flow into the water heater (10) from the upstream side of the exterior circuit.