MIL-STD-1411B
5.3.2.6.1.2 Valve inlet and outlet connections. Valves with less than one thread previously mated in cylinder installation shall be rejected and replaced (see 5.3.2.1). Valve outlets must have smooth seats that are free of nicks or dents on the sealing surfaces. Threads will be free running in the mated connections. Outlets shall be in accordance with the CGA V-1 and the contract or work order.
5.3.2.6.1.3 Valve outlet caps and plugs. Outlet caps or plugs shall be provided for toxic gas service in accordance with A-A-59860 and the applicable associated specification sheet. When specified in the contract or work order for nontoxic service, caps or plugs shall be provided in accordance with A-A-59860.
5.3.2.6.2 PRDs. The PRD for each valve shall be in accordance with A-A-59860 and for the service specified in the PID. Mismatched, leaking, or extruded PRDs shall be replaced as complete units (cap, disk, and washer). A faulty PRD, which is integral to the valve body, is cause for replacement of the valve. The combination rupture disk, burst pressure 2,700-3,000 psig, backed with fusible metal (CG-4 or CG-5) as applicable, is an authorized PRD for
cylinders with marked service pressures 1,800 through 2,400 psig. This PRD meets all requirements of the DOT and the recommendations of the CGA for compressed high-pressure gas applications when used in accordance with A-A-59860. The combination PRD shall not be used for cryogenic liquid sample cylinders or with any cylinder that has been tested and stamped with a "+" sign after the last hydrostatic test or UE date. The "+" sign indicates that the cylinder may be filled to a pressure 10 percent above the marked service pressure, and therefore the use
of a rupture disk PRD is mandatory regardless of whether the cylinder is pressurized to a higher level or only to the marked service pressure. An CG-1 rupture disk for the specific service pressure marked on the cylinder, when applicable, is the preferred PRD.
5.3.2.6.3 Valve installation. All valves shall be installed in cylinders using thread tape. The use of anti-sieze thread compounds is authorized for cylinders in hydrogen or helium service where molecular size may diminish the capability of thread tape to effect a proper seal. All oxygen valves and high-pressure valve services shall be installed with one to three turns of polytetrafluoroethylene tape conforming to A-A-58092. Prior to applying tape or thread compound, the valve's inlet threads shall be cleaned of possible cylinder contaminants. One thread should remain exposed at the lead end of the inlet threads when applying tape or thread compound to ensure against cylinder contamination. Fluorocarbon lubricants that are stable in oxygen atmospheres may be used to increase the effectiveness of the polytetrafluoroethylene
tape. Hydrocarbon lubricants are prohibited in compressed gas service. All valves should be installed and torqued until a maximum of five and not less than one full thread shows above the cylinder. New valves should have as near five threads showing as is possible to effect a tight seal. When a valve is reinstated in its mated cylinder, a reliable seal can be achieved by torquing the valve one-half to one full thread into the cylinder beyond its previous installation. Used valves should seal displaying one to two threads less than with any previous installation. If a
gas-tight seal cannot be achieved through a reasonable application of the above guidelines, the cylinder shall be rejected and marked condemned for enlarged neck threads. Except for chlorine service, oversized valve inlet threads are not approved in the government system.
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