Abstract: A slow acting pneumatically operated valve which uses gas pressure and/or pneumatic pressure acting on a diaphragm to counteract the force of a coiled spring, thereby activating a double tapered fluorocarbon plastic poppet against a fluorocarbon plastic valve seat. Actuation of the poppet must be extremely slow and uniform such that fluid in the affected supply line does not experience shocks which can be transmitted to other supply line components. Actuation speed is restricted by use of a damping piston attached to the opposite end of the poppet stem, which restricts the flow of hydraulic fluid to opposite sides of the piston chamber during an actuation cycle. The double taper poppet incorporates an extremely low angle of incidence to the valve seat. Valve opening increases very slowly during the initial opening travel and decreases slowly during final closing travel, thereby further reducing the potential for fluid system shocks.