A pilot valve for controlling operation of a fluid-actuated pressure reducing valve, the pilot valve including: a housing, a first valve member and a second valve member whose relative positions control flow through the pilot valve;Instrumentation Ball Valves the first valve member being provided on a movable actuating member which is mounted in the housing for movement relative to the housing in response to the outlet pressure of the pressure reducing valve, movement of the actuating member changing the relative positions of the first and second valve members; and an adjuster for varying the relative positions of the first and second valve members for a given position of the actuating member,Reducing Valves so as to cause the output pressure of the pressure reducing valve to alter; wherein one of the first and second valve members includes an aperture; the other of the first and second valve members includes a blocking portion which is arranged for relative sliding movement across the aperture to vary the flow cross section through the aperture and thus the flow through the pilot valve; SAFETY VALVES and the adjuster is arranged to adjust the relative positions of the blocking portion and the aperture by sliding movement so as to adjust the flow cross section through the aperture for a given position of the actuating member. Alternatively and preferably the first valve member may be in the form of a longitudinally extending tubular member which is in fluid communication with a control chamber of the pressure reducing valve and which has an aperture controlled by the blocking portion, the outlet from the aperture being in communication with the outlet pressure of fluid from the pressure reducing valve.

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