Abstract: A fluid pump assembly having a body provided with a fluid chamber and a passage having an orifice, the passage connecting the chamber to a conduit carrying a pressurized flow of fluid. Pump apparatus has an inlet connected to a fluid additive supply, and an outlet which communicates with the conduit for feeding the fluid additive to the conduit. Control apparatus includes a dump passage communicating with the chamber and has a cross section larger than the orifice. A dump valve controls the flow of fluid through the dump passage to regulate the fluid pressure in the fluid chamber, and motor apparatus operatively connects the pump apparatus and the dump valve. The motor apparatus is responsive to the fluid pressure in the fluid chamber for operating the dump valve and actuating the pump apparatus to pump fluid additive through the outlet.