A metering apparatus for controlling the rate of closure of a pressure-actuated valve of a type normally used in irrigation systems. When a pressure-actuated valve is closing, fluid from a supply line must flow into a pressure-actuating chamber, gradually filling it to force the valve's plug member against...http://www.google.de/patents/US4206901?utm_source=gb-gplus-sharePatent US4206901 - Pressure-actuated valve with metering choke
