A bonnet is mounted on an insert support and connected to a valve body to retain a diaphragm in fluid sealing relationship between the body and insert support. The insert support is rotatable relative to the housing of a fluid actuator while being retained in a fixed axial position relative to the housing. A plunger is extended through the insert support to abut against a button that abuts against one side of the diaphragm, the opposite side of which abuts against a valve seat subassembly that is resiliently urged to a valve open condition. The housing mounts a spindle which in turn has an eccentric lobe keyed thereto for moving the plunger toward the diaphragm so that the button flexes the diaphragm to move the seat subassembly to its valve closed position. Piston operated rack mechanism controls the rotation of the lobe for moving the plunger toward the diaphragm. Spring mechanism moves the piston in one direction while fluid under pressure applied to the actuator moves the piston in the opposite direction. The spindle and lobe may be selectively positioned in the housing so that the actuator is for a normally open valve or a normally closed valve. One of the embodiments is of a construction for fitting under a cap of a gas cylinder and replacing a manually operated control valve whereby the flow from cylinder can be controlled from a remote location.