packing in the ordinary valve by providing a metal bellows (Sylphon), which prevents liquid from escap- ing through the valve stem opening. Sylphon packless globe valves are used in the pump room on the drainage piping from the centrifu- gal pumps, on other small-diameter pipelines carrying gasoline or nitrogen, and on steaming-out connec- tions. The Sylphon packless globe valve controls the flow of liquid the same way as an ordinary globe stop valve. When the control handle is turned, a poppet at the end of the valve stem is lifted from a valve seat and permits flow through the valve. It has an expand- able, metal bellows (or Sylphon) assembled between the valve poppet and the bonnet cap nut. This permits the valve stem to be raised or lowered while maintain- ing a complete seal around the stem at all times. In the ordinary globe valve, a fiber packing is used to pre- vent the escape of liquid. This packing deteriorates or shrinks and allows dangerous leakage of liquid or vapor. The Sylphon bellows may be replaced if it corrodes or breaks. PROTECTIVE SYSTEM Nitrogen (N2) or carbon dioxide (COZ)  is used in cofferdams as a protection against fire and explosion, in double-walled piping to indicate the condition of the double-walled piping, and in the distribution pip- ing for drainback, purge, and charge. On LHAs, nitrogen was capable of being pro- duced aboard the ship, but most of the production plants are no longer operable. Instead, it must be earned in 3000 lb bottles. Other class ships also must carry NZ and/or COZ in compressed-gas bottles and the inerting process is slightly different. Consult CFOSS for the correct procedures on your ship. Nitrogen enters the pumproom reducer at 50 psi from the nitrogen supply room. To purge and inert the MOGAS piping, the reducer is bypassed and the pip- ing is charged directly from the nitrogen supply line. The gages must be monitored to make sure the pres- sure does not exceed 10 psi. The MOGAS piping is required to be inerted with a 50% N2 inert gas concen- tration at 10 psi. The reducer is used to reduce the NZ pressure from 50 psi to 3 psi for inerting the double-walled piping, the cofferdam, and the gasoline tank (after deballasting). The double-walled piping, cofferdam, and gasoline tank (when deballasted) are required to be made inert with a 50% inert gas concentration at 3 psi. The pressure relief valve for the piping/double- walled piping is set at 14 psi. The pressure relief valve for the cofferdam is set at 7 psi. NOTE Ships using carbon dioxide in place of ni- trogen purge to 35% inertness minimum. INERT-GAS-PRESSURE REGULATING VALVE The inert gas regulating valve consists of a dome and body separated by a rubberized dia- phragm. The diaphragm actuates The poppet valve in the valve body by forcing down the valve stem. A compression spring below the poppet valve tends to return the valve to its seat against the force of the diaphragm. The dome is filled with inert gas under pressure when the valve is adjusted. This gas pres- sure acts on the upper surface of the diaphragm. A pressure chamber on the underside of the diaphragm fills with nitrogen through an opening to the dis- charge, or low pressure, side of the valve. Thus, when the valve has been adjusted and is in opera- tion, the pressure on the upper side of the dia- phragm acts to force the valve open. This force is balanced by the low-pressure gas on the underside of the diaphragm and the spring under the poppet valve. When low-pressure gas is taken from the system, the pressure on the discharge side starts to fall, and the regulating valve opens to permit pas- sage of gas from the high-pressure side of the valve. The distance the valve opens depends on how fast the low-pressure gas is being used. When use of low-pressure gas is stopped, the pressure on the underside of the diaphragm starts to increase, and the valve closes to stop the flow of high-pressure gas. When the regulating valve is being adjusted, ni- trogen gas from the high-pressure side of the valve is admitted to the dome chamber through an orifice controlled by two needle valves (fig. 6-14). A ball relief valve to the orifice will release gas if the high- -pressure needle valve in the body is opened too far. 6-16