Cartridge assembly with orifice providing pressure differential

A cartridge assembly for use in a pump, said cartridge assembly comprising:

• a housing to be secured to the pump, said housing including surface means for defining a fluid inlet through which fluid from a working chamber of the pump enters said cartridge assembly and surface means for defining a fluid outlet through which fluid flows from said cartridge assembly to a system to be supplied with fluid by the pump;
• orifice means disposed in said housing and connected in fluid communication with said fluid inlet and said fluid outlet for establishing a pressure differential in fluid flow from said fluid inlet to said fluid outlet;
• a fluid bypass port formed in said housing to conduct excess fluid flow from said cartridge assembly;
• flow control valve means disposed in and movable relative to said housing for controlling fluid flow through said bypass port, said flow control valve means being movable relative to said housing in response to changes in the fluid pressure differential established by said orifice means to vary the rate of fluid flow through said bypass port;
• and
• pressure relief valve means disposed in said housing for effecting a reduction in the fluid pressure at said fluid outlet, said pressure relief valve means being operable from a closed condition blocking fluid flow to an open condition under the influence of fluid pressure in excess of a predetermined fluid pressure at said fluid outlet, said flow control valve means including passage means for conducting fluid flow from said pressure relief valve means to said bypass port when said pressure relief valve means is in the open condition.