Liquid shut-off valve

An automatic shut-off valve suitable for watering of batteries is disclosed. The valve is formed by a chamber having an inlet and an outlet. A seat surrounds the outlet. A spring biased piston within the cylinder is movable into and out of sealing engagement with the seat to open and close the valve. A flow deflecting surface is positioned between the inlet and the piston. Water flow is directed around the piston to eliminate drag that would force the piston into engagement with the seat. A second deflector surface directs flow against the piston to bias it open. An actuator cup, fed by a nozzle extending from the outlet, draws the piston into engagement with the seat when the cup is sealed by engagement with the electrolyte surface. The valve may also employ a float actuator connected to the piston.