Page 169 - Boiler_Operators_Handbook,_Second_Edition

154 Boiler Operator’s Handbook

vaporize any accumulation of liquid refrigerant. The op- lubricating oil that lubricates and cools the seal has been
eration of the accumulator means oil level can fluctuate interrupted.
and it’s wise to observe the oil level for a while before
reacting to a slightly higher or lower level by adding or Reciprocating Compressors
removing oil. Reciprocating compressors are the most common
Compressors are classified as open, hermetic, or type of compressor. One in your car, a window unit,
semi-hermetic. Virtually all small compressors are her- your refrigerator or freezer typically contains two pis-
metic with the motor enclosed within the sealed com- tons and cylinders. Figure 5-6 is typical of reciprocat-
pressor casing. Since the motor is enclosed within the ing compressors used for home air conditioning units.
compressor casing the motor is cooled by the refrigerant I have operated and maintained compressors with as
flowing over it. A continuous flow of cool refrigerant many as 16 cylinders, units similar to the one in Figure
while the compressor is operating is essential to pre- 5-7a & b which has 8 cylinders. Note the head spring in
vent the motor overheating. Small compressors like the the section which reveals that the head of each cylinder
one in your refrigerator, window unit, and residential in these compressors is free to move within the cylinder,
air-conditioners will not have means of monitoring con- compressing that head spring whenever liquid might be
ditions to detect a loss of refrigerant flow. However, an- drawn into the compressor cylinder. A louder “thump”
other sense attributable only to a person, can provide an (actually it’s more of a bang or rattle) is a sign that’s hap-
indication of a problem: your sense of smell. If the motor pening to one of them. Reciprocating compressors func-
is not cooled adequately the higher temperature will re- tion by the movement of the piston and cylinder to first,
sult in vaporizing whatever managed to accumulate on increase the volume inside the cylinder which allows the
the outside of the compressor casing producing a hydro- gas in the cylinder to expand until the pressure in that
carbon emission that you recognize. Regular rounds by cylinder is lower than the pressure at the compressor in-
an experienced operator can usually result in detection let. Then gas from the evaporator flows into the cylinder
of a problem and action to rectify it before the equip- as the moving piston makes room for it. Gas enters the
ment fails even if there are no gauges or
thermometers to read.
Medium sized and large compres-
sors can be of any type but, because
most of them are constructed to permit
maintenance they are called semi-her-
metic. Flanged and threaded connec-
tions permit opening the compressor
enclosure for maintenance.
Large compressors are either
semi-hermetic or have the motor mount-
ed outside of the compressor casing in
which case they are referred to as open
compressors. Because your automobile
air conditioner is driven by a belt and
pulley from the engine it’s an open com-
pressor. An open compressor requires a
shaft seal which can become a repeating
maintenance problem. There are restric-
tions on the amount of refrigerant that
can leak from a system and shaft seals
are normally the only source of leaks.
If you have an open compressor and
repeated seal failures it’s an indication
that they are not installed properly, the
compressor and motor are not in align-
ment, or the flow of refrigerant and/or
Figure 5-6. Small Reciprocating Compressor