Revision: 09/2014
W 3552-6.02e.E
Page 7 / 16 MWi
Instruction manual
BDP2
6.4
HOT GAS LINE
Preferably, the hot gas supply should be taken between oil separator and condenser (see “system schematic”, 6.10,
tapping point
A
). Alternatively, a WITT high side float is suitable because warm gas is collected with sufficient pres-
sure at the top regulating valve (see “system schematic”, 6.10, tapping point
B
).
In both cases, the control line that is fed from a solenoid valve should be installed near to the BDP2, because
a)
larger quantities of condensate may collect in front of the solenoid valve, but only refrigerant vapor is
allowed for the cycle.
b)
The small volume of the control line between solenoid valve and BDP2 reduces the time for the return of the
internal piston (mechanical valve) to the initial position upon completion of a successful operation of one
cycle.
The internal damping of the BDP2 allows use of hot gas at high pressures.
6.5
DISCHARGE OF REFRIGERANT/OIL MIXTURE
Due to the hot gas supply, an internal piston closes the connection to the low-pressure side of the refrigeration sys-
tem and pressure is build up within the BDP2 housing. Any liquid within the BDP2 is pushed outwards through a
check valve towards the compressor side.
6.6
HEAT EXCHANGER AT THE BDP2 OUTLET
We strongly recommend to pass the pushed out refrigerant/oil mixture through a heat exchanger to ensure that all
liquid refrigerant has been evaporated before returned to the compressor. The heating capacity should be adequately
selected such that any liquid refrigerant is completely evaporated. Sufficient time for evaporating should also be con-
sidered, when an optional level senor is used to control the cycle.
WITT flow through evaporator DWR or small oil collectors, heated electrically or with hot gas, are proven for this
purpose (see “system schematic”, 6.10,
DWR
).
6.7
OIL RETURN TO THE COMPRESSOR
The oil return should be located within or before the compressor, where the pressure is slightly lower than the pres-
sure within the BDP2 housing.
The engineer in charge of the design should select an appropriate location for the oil return – depending on the type
and make of compressor. The following locations have been proven good practice:
Screw compressors: in the suction line right in front of the suction stop valve (see “system schematic”, 6.10,
Position
Y
)
Piston compressors: in the return line between oil separator and crank case (see “system schematic”, 6.10,
Position
X
)
When using evaporation pressure regulators it is important that the pressure does not get too low. When the pres-
sure difference to open the check valve (3 bar respective 1 bar) is reached, it is possible to continuously suck liquid
refrigerant from the surge drum through the BDP2.
If a fine filter (e.g. WITT oil-filter ÖF) is required in the oil return line depends on the execution/cleanliness of the
entire system. This should be evaluated by the design engineer.
We recommend to install a sight glass after the heat exchanger. This will enable the proper observation of the oil
return.
