Abstract: A double acting pneumatically operated pumping assembly for pumping viscous fluids, especially food stuffs, is provided. The piston has an enlarged central portion integral with reduced diameter end portions. Inspection means, for example vent ports, are provided between seals of each end portion so that any leakage of either pneumatic fluid or of viscous fluid is detectable. The pump is preferably of modular form, each module having flanged ends and hand-tightenable band clamps holding the flanges together for easy assembly and disassembly. A feature of the invention is an operating valve having pilot chambers at each end for control of the spool position. Movement of pilot pistons within the pilot chambers affects the pressure balance between ends of the spool. Changes in pressure may be derived from the piston chamber of the pump from ports located to change the pressure balance of the valve when the pump piston has completed its stroke.