GENERAL DESCRIPTION
Page 2-28
CASCADE UNIT - SYSTEM 2 (R-508B) DESCRIPTION
The compressor (item 41) will pump compressed R-508B vapor through the discharge line where the high
pressure gauge senses the pressure of the refrigerant. The high pressure switch (item 95) senses the
discharge refrigerant pressure and will open a contact in the event that discharge pressure exceeds 350 psig
This contact opening will serve to shut down the unit and will automatically reset when the pressure drops to
250 psig (17.2 barG).
The discharge refrigerant vapor passes through the oil separator; the oil separator (item 45) removes the oil
in the refrigerant vapor. It collects the oil and drains it back to the compressor crankcase. This prevents oil
logging in the evaporator. This discharge vapor then passes through the desuperheating loops. If the unit is
air-cooled, the desuperheater (item 45), is part of the air-cooled condenser (item 5). If the unit is water-cooled,
the
desuperheater is a separate component. The discharge refrigerant vapor then enters the cascade condenser.
The cascade condenser (item 13) cools the high pressure R-508B vapor and condenses it into a high
pressure liquid.
High pressure liquid refrigerant exits the cascade condenser. The liquid • ows through a • lter-drier and enters
a tee. The tee will divert some of the liquid refrigerant to be used in the bypass circuit (see last paragraph of
this section). The rest of the refrigerant passes through the liquid line solenoid valve (item 49) and into the
T.E.V. (item 50) where it changes into a low pressure two-phase refrigerant. The two phase refrigerant is cold
due to the • ashing of refrigerant. It enters the distributor (item 51) where the refrigerant is evenly distributed
to the evaporator circuits. The evaporator (item 52) serves to boil the rest of the R-508B into a vapor. This
boiling action cools the chamber. System 2 is not in operation during humidity mode.
Superheated R-508B/R-23 vapor exits the evaporator and moves through the system 2 suction line. A service
valve is located near the compressor.
The bypass circuit is composed of two lines in parallel. The Hot Gas Bypass Line, and the Liquid Injection
Line. The hot gas bypass line consists of a solenoid valve (item 62) and Hot Gas Bypass Regulator (item 63).
The liquid injection line consists of a Liquid Injection T.E.V. (item 61). The hot gas bypass solenoid (item 62)
will open and close opposite of the liquid line solenoid (item 49). It will allow hot discharge refrigerant vapor to
• ow directly to the suction line. This is done as a means to control cooling capacity or to “unload” the system.
The liquid injection T.E.V. will sense the temperature of the suction line. It will open automatically to feed
liquid refrigerant into the suction line. This will provide cooling for the hot gas that is being fed into the suction
line. The cooling effect keeps the compressor from overheating.
On cascade systems using scroll compressors, there is also a discharge temperature control valve (item 78).
This DTC valve receives liquid refrigerant from the liquid line and injects it into the scroll compressor. This
prevents the compressor from overheating and results in no loss of capacity or mass • ow.
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