Abstract: A constant-flow valve assembly having a first passageway carrying fluid at a first pressure, a piston chamber, and a second passageway connected to the chamber and carrying fluid at the second pressure. A third passageway carries fluid at a third pressure. An adjustable valve is between the chamber and the third passageway, and an adjustable restrictor is positioned between the first and second passageways. An inlet portion of the restrictor assembly receives fluid at the first pressure and directs the fluid to a restrictor, and outlet portion directs the fluid to the second passageway at the second pressure. The restrictor is movable to adjust the position of entry and exit portions relative to the inlet and outlet portions to adjust a fluid flow rate to the second passageway to adjust the flow rate through the valve assembly.