An external stationary bellows crankshaft seal is
shown in figure 6-16. This seal is the same as the
internal seal, except it is positioned on the outside of
An external rotating bellows crankcase seal is
shown in figure 6-17. This seal turns with the
crankshaft. This seal also consists of a corrugated thin
brass tube (seal bellows) with a seal ring fastened to
one end and a seal flange fastened to the other. A seal
spring is enclosed within the bellows. The complete
bellows assembly slips on the end of the crankshaft and
is held in place by a nut. The seal ring that is the inner
portion of the bellows is positioned against a
nonrotating seal fastened directly to the crankcase.
During operation, the complete bellows assembly
rotates with the shaft, causing the seal ring to rotate
against the stationary seal. The pressure of the seal
spring holds the seal ring against the seal. The
expansion of the bellows caused by the pressure from
the crankcase also exerts pressure on the seal ring.
Because of this design, double pressure is exerted
against the seal ring to provide a gastight seal.
hermetically sealed compressor, the electric motor and
compressor are both in the same airtight (hermetic)
housing and share the same shaft. Figure 6-18 shows a
hermetically sealed unit. Note that after assembly, the
two halves of the case are welded together to form an
airtight cover. Figure 6-19 shows an accessible type of
hermetically sealed unit. The compressor, in this case,
is a double-piston reciprocating type. Other
compressors may be of the centrifugal or rotary types.
Figure 6-16.An external stationary bellows crankshaft seal.
Figure 6-17.An external rotating bellows crankcase seal.
Cooling and lubrication are provided by the circulating
oil and the movement of the refrigerant vapor
throughout the case.
The advantages of the hermetically sealed unit
(elimination of pulleys, belts and other coupling
methods, elimination of a source of refrigerant leaks)
are offset somewhat by the inaccessibility for repair
and generally lower capacity.
The condenser removes and dissipates heat from
the compressed vapor to the surrounding air or water to
Figure 6-18.Hermetic compressor.