Abstract: A dispensing pump of the pressure build-up variety includes a cylinder defining a variable volume pump chamber, and a main piston reciprocable therein, the piston having a valve seat thereon communicating with a discharge passage leading to a discharge nozzle. A valve member having a smaller diameter piston thereon is moved during pressure build-up away from the seat for opening the discharge passage. The smaller diameter piston has a flexible peripheral wall which is deformed inwardly at the commencement of the piston downstroke for closing a flow passage in the smaller diameter piston and thereby interrupting communication between the inlet and the pump chamber, such flow passage being open upon outward movement of such peripheral wall at the end of the piston upstroke. At the top of the cylinder along which the smaller diameter piston moves is a relieved section effecting the opening of the flow passage in an inoperative condition of the pump.