8.
COMPRESSORS/TRANSFER PUMPS. Commercially available compressors
presently being used for compressing or transferring helium, oxygen, or
helium-oxygen mixtures are diaphragm-type compressors. The diaphragm
compressor is a combination of two systems, hydraulic on one side of the
diaphragm, and breathing gas on the other. The hydraulic system provides the
force to move the diaphragm, which in turn compresses the gas.
CAUTION:
A system should be provided to positively and
rapidly detect the rupture or failure of the
diaphragm, before the hydraulic fluid can contaminate
the pumped gas. It should be so
designed that an interlock circuit will shut down
the compressor when failure is detected.
A compressor should incorporate a by-pass check valve, for equalizing
pressure across the diaphragm before compressor startings, and a vent to
atmosphere immediately downstream of the discharge valve. Gas from
compressor/transfer pumps should pass through a back pressure regulator
designed to handle the maximum required compressor flow and set at desired
flask charging pressure.
System requirements needed to select a compressor/transfer pump include
suction pressure, discharge pressure, suction gas temperature, materials, and
capacity.
9.
GAS MONITORING. The quality of the compressed gas should be
continuously, or at least periodically checked to assure that low contaminant
requirements are maintained. The contaminants, which should be monitored in
the chamber are CO2, oxygen, and hydrocarbons. Levels and ranges of the
various chamber gasses and contaminant limits are discussed in Section 1,
Paragraph 2, Breathing Gas Composition Requirements.
Gas analysis equipment is available from various manufacturers for use in
testing gas samples for contaminants. Figure 6-24 shows how gas samples are
taken from the chamber, reduced to 15 psig, and fed through a capillary line
to the analysis equipment to rapidly detect any change in the gas.
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