Abstract: There is shown and described a valve which maintains a constant flow of fluid through a fluid passage even though input pressure varies in the fluid passage. The valve includes a body which has a progressively decreasing cross-sectional area therein between the respective inlet and outlet portions. A moveable damper in the valve automatically moves to alter the area between the damper and the valve body thereby to control the free area of fluid flow through the body. Thus, constant flow through the valve body is maintained despite pressure variations at the inlet portion. The valve configuration permits easy adjustment of fluid flow therethrough.