Heatcraft Refrigeration Products PARALLEL COMPRESSOR SYSTEMS 25000102 - Manual (Page 26)

26 Part # 25000102
Installation and Operations Manual
Module Replacement
1. Disconnect power at the fuse box
2. Remove wiring box from the retainer
3. Remove the IRR 4000-93 Ring with an IRR P-101 or equivalent
retaining ring pliers
4. Remove the Retainer
5. Pull out the module by the leads
6. Install new Module
7. Verify the voltage rating
8. Reassemble the Retainer, Ring, and wiring
Oil Control
A proper oil control system is essential to insure compressor
lubrication. An oil control system can be very cost effective
alternative to replacing expensive compressors due to loss of
oil. Oil traveling through the system tends to build up in the
evaporator, condenser, and vessels of a refrigeration system.
This causes a lack of oil return to the compressor until finally, a
large amount returns as a “slug” of oil.
A slug of oil down the suction line can be just as damaging to
the compressor as a slug of liquid refrigerant. This delay in oil
return requires an additional amount of oil to be added to the
system, depending on the size of the system, the piping, the
temperatures, the miscibility of the refrigerant/oil mix, and the
refrigerant velocity.
By removing oil from the discharge gas of compressors, not
only is the oil level for each compressor more accurately
controlled, the efficiency of the system is increased. Oil does
not change phase from liquid to gas in a refrigeration system
and therefore makes a very poor refrigerant. Oil also takes up
volume through the system that otherwise could be filled with
refrigerant. Additionally, oil tends to film the condenser tubing
wall lowering heat transfer and as oil and refrigerant exits the
expansion valve, the oil will foam insulating the evaporator
walls and again lowering heat transfer.
IMPORTANT: An oil control system does not replace
the need for proper system design. An
oil control system will drastically reduce
the amount of oil going through the
system. Correct piping, suction traps,
and proper sizing of valves, controls, and
components must still be implemented
to insure the system will work properly.
Low Pressure Oil System
This type system is normally used for parallel compressors and
uses three basic components: Oil Separator, Oil Reservoir, and
Oil Level Regulators. The common discharge is piped to the
inlet of the oil separator and the outlet of the oil separator is
piped to the condenser. An oil return line is brought from the
oil separator to the top valve of the oil reservoir. A vent line is
installed to the suction line with a pressure valve in line to lower
the pressure in the reservoir, making a low pressure oil system.
This valve will keep the reservoir pressure a set pressure above
suction depending on the value of the valve, either 5 or 20 psig
to the oil level regulator. Mechanical oil level regulators are
rated for pressures ranging from 5 to 90 psig differential. The
bottom valve of the oil reservoir is piped to oil level regulators
mounted on the compressor crankcases. These regulators open
to feed oil as the oil level drops and closes as the oil level raises
to the set level. In this manner, the oil level in the compressor
is kept at a constant level. Either one oil strainer per regulator
or one oil filter per separator must be used to remove debris
from the oil.
Oil Separators
There are two types of oil separator that may be used in
the Heatcraft parallel racks. One type utilizes the standard
impingement screen. This type separator works by having the
compressed mass flow enter into a large separator chamber
which lowers the velocity and then the atomized oil droplets
collect on the impingement screen surface. As the oil droplets
collect into larger particles they fall to the bottom of the
separator.
The second separator more commonly used is the coalescent
type. This type separator contains a matrix type borosilicate
coalescent filter to do the work impingement screens formerly
did. The exceptionally pure, extremely fine glass fibers matrices
excite the oil molecules to collide into one another thus
agglomerating them into bigger droplets until they are forced
to the outer drain layer of the filter. These droplets fall to the
bottom of the separator reservoir and the oil is then returned
Figure 15.
Figure 16. Low Pressure Oil System