Piston hydraulic water Level control valve, is a kind of automatic control tank, water tower level of hydraulic control valve. When the water surface falls above the preset value, the float valve opens, the piston upper chamber pressure is lowered, the piston up and down formed pressure difference, the valve flap open for water supply operation under this differential pressure; when the water level rises to a predetermined height, the float valve closes, and the pressure on the upper chamber of the piston increases, causing the disc to shut down. So reciprocating automatic control of the level in the set height, to achieve automatic water supply function. This product is suitable for the automatic water supply system of various water tanks (pools) and towers in industrial and mining enterprises and civil buildings. And can be used as pressure boiler circulating water supply control valve.