air, if the cylinders cool considerably below the
temperature at which they were discharged.
Sometimes, cylinders used for aviator's breathing
oxygen, dry nitrogen, argon, or dry air are found to
have open valves and/or a positive internal pressure of
less than 25 psi. These cylinders should be tagged with
the explanation that they must be dried before they are
refilled.
GAS CYLINDER VALVES
Navy standard gas cylinder valves are of two basic
designs: packed valves and diaphragm-type packless
valves.
Packed valves require a packing material around
the valve stem to prevent leakage. The valve stem is
packed to prevent gas from leaking out around the
Figure 5-68.--Oxygen cylinder gas valves: (A) external view of
stem when the valve is open. MIL-V-2 covers the
one type of valve, with related safety and outlet connection
authorized packing material for gas cylinder valves.
caps; (B) cutaway view of the same valve, showing
diaphragms to prevent gas leakage when the valve is
Packless valves are sealed against leakage around
opened; (C) cutaway view of another type of valve, with
the valve stem by flexible metallic diaphragms
asbestos packing to prevent gas leakage when the valve is
securely clamped to the valve bonnets. The basic
opened.
packless design may be classified into two types:
nonbackseating and backseating. The nonbackseating
gas flows through a threaded male cylinder connection
type is designed so that the metallic sealing
into the valve body and past the valve outlet
diaphragms may not be replaced under pressure. In the
connection into the pressure regulator. (Pressure
backseating type the metallic diaphragms may be
regulators reduce the pressure of compressed gases
replaced without undue hazard or loss of contained
from the cylinder pressure to the desired working
gases if the outlet cap is in place and secure.
Diaphragms in packless valves should be replaced
only by activities carrying spare diaphragms
specifically designed for the valves in need of
reconditioning.
These diaphragms are made from materials
selected for service at varying high pressures. In
addition, they are often designed only for use with
valves built by a given manufacturer and for a specific
gas.
The Navy gas valve program (and concerned
civilian agencies) provides noninterchangeable valve
outlets and connections for different gases to prevent
the use of the wrong gas at any time.
Construction and Identification of Valves
Valves designed to control the flow of compressed
gases are forged of brass, bronze, or steel, and are
made in various shapes and sizes. Figures 5-68 and
5-69 show typical gas cylinder valves. The valves are
opened and closed with either hand-operated or
Figure 5-69.--Cutaway view of an acetylene cylinder valve
wrench-operated spindles. When the valves are open,
showing asbestos packing.
5-47