(fig. 6-50). The pump is used to reduce the pressure in a
refrigeration system to below atmospheric pressure.
Various manufacturers manufacture hermetic
refrigeration systems used by the Navy; therefore, the
connectors and size of tubing vary. The Table of
Allowance provides for a refrigeration service kit that
contains several adapters, wrenches, and other
materials to help connect different makes of systems to
the refrigerant manifold gauge set and the vacuum
pump lines. A table affixed to the lid of the storage
container identifies the adapter you should use for a
particular refrigeration unit.
Figure 6-50.Portable vacuum pump.
Refrigerants are shipped in compressed gas
cylinders as a liquid under pressure. Liquids are
usually removed from the shipping containers and
transferred to a service cylinder (fig. 6-51).
Before attempting transfer of refrigerants from a
container to a cylinder, precool the receiving cylinder
until its pressure is lower than that of the storage
container or cylinder. Precool by placing the cylinder
in ice water or a refrigerated tank. You must also
weigh the service cylinder, including cap, and compare
it with the tare weight stamped or tagged on the
cylinder. The amount of refrigerant that may be placed
in a cylinder is 85 percent of the tare weight (the weight
of a full cylinder and its cap minus the weight of the
empty cylinder and its cap).
To transfer refrigerants, connect a flexible
charging line on a 1/4-inch copper tube several feet
long with a circular loop about 8 to 10 inches in
diameter. Be sure to install a 1/4-inch refrigerant
shutoff valve (fig. 6-51) in the charging line to the
service cylinder. This valve should be inserted so no
more than 3 inches of tubing is between the last fitting
and the valve itself. This arrangement prevents the loss
of refrigerant when the service drum is finally
disconnected. The entire line must be cleared of air by
leaving the flare nut on the service cylinder loose and
cracking the storage cylinder valve. This arrangement
allows refrigerant to flow through the tubing, clearing
it. After clearing, tighten the flare nut and then open
the valve on the service cylinder, the valve on the
Figure 6-51.Method of transferring refrigerants to service cylinders.