Abstract: An improved constant volume flow device wherein the device includes a body defining a flow passage with an inlet portion and an outlet portion. The body is adapted to conduct a flow of fluid through the passage wherein such flow has a varying pressure at the inlet portion. A restricting member in the flow passage for axial movement therealong to regulate the fluid flow through the passage is also provided. The improvement includes the provision of means for varying the value of the constant volume of fluid flow of the device. Further, a progressively decreasing portion may be formed between the inlet and outlet portions and this shape, as affected by the varying value means, may be given by formulas.