Zero Governor Regulator : A gas pressure regulator equipped with a counter spring beneath the valve; it requires an external impulse signal such as top loading with pressure or generating vacuum in the downstream piping
NFPA 37 Standard for the Installation and Use of Stationary Combustion Engines and Gas Turbines, 2002 ed. http://pozhproekt.ru/nsis/nfpa/NFPA37-2002.pdf, (Std: Install and Use of Stnry Combustion Engines and Gas Turbines - Amer) {201 NFC}