Abstract: A pump for a pressure washer. The pump includes a cam housing, a piston assembly disposed within the cam housing, a rotary shaft assembly disposed within the cam housing, a journal plate attached to the cam housing, a head assembly attached to journal plate and valve assembly operatively connected to the head assembly. The rotary shaft assembly includes a cam shaft, a vertically-extending oil tube partially disposed within a central portion of the cam shaft, a cam threaded onto the cam shaft and a thrust washer positioned adjacent the threaded cam. The piston assembly includes a plurality of pistons, preferably three, in mating contact with the thrust washer. Each piston includes a piston spring cap at one end, a spring disposed over the piston and engaging the piston spring cap, and a seal retainer having a low pressure seal at one end and a high pressure seal at the other end.