Abstract: A high pressure valve assembly has a bore with a seat intermediate its ends and an inlet on one side an outlet on the other side of the valve. A double headed piston within the bore has a closure head between the seat and the outlet and a control head on the other side of the inlet to the seat. The control head has a slightly greater projected surface area facing towards the seat than the closure head. There is a cage between the seat and the outlet, which defines an annular chamber about the bore between the seat and the outlet, the chamber opening into the outlet. The cage has a number of rings of apertures spaced from the seat which are successively opened as the closure head moves away from the seat. The closure head extends beyond the apertures and has a "U"-seal at its downstream end. The control head also has a "U"-seal. The seals face towards the seat. The bore is closed by end caps. The valve assembly is manually operable or by means of a control fluid.