 Poppet valves are employed extensively in the launching of torpedoes from submarines.Many systems use compressed air to expel the torpedo from the tube, and the poppet valve recovers a large quantity of this air (along with a significant amount of seawater) in order to reduce the tell-tale cloud of bubbles that might otherwise betray the boat's submerged position.Poppet valves are used in most reciprocating engines to open and close the intake and exhaust ports in the cylinder head.