Abstract: A pump comprises an open-ended hollow body defining a pump chamber and an inlet orifice which communicates with a reservoir. The pump body has four side walls. A piston is mounted for reciprocal movement through a portion of the body and it extends through the upper end of the body. A ferrule is disposed above the body and defines an aperture through which the piston extends. A seal is disposed is disposed between the ferrule and the body, and the seal surround a portion of the piston. A spring is mounted in the body, and the spring actively biases the piston toward the top of the body. The body has a deformable zone which has at least a portion of one side wall which is a noncircular cross-section and is radially elastically deformable. The piston has a portion which blocks the inlet orifice when the piston is depressed a first predetermined distance.