8
D6.3.4/0715-0716/E
Discus
Figure 2
This family consists of refrigerant-cooled single-stage compressors, models 2D, 3D, D4D, D6D
and 8D with 2, 3, 4, 6 and 8 cylinders and a displacement between 22.4 m³/hr and 181 m³/hr.
All compressors are fitted with Discus valve plates which cannot be dismantled. To maintain the
high capacity of these compressors the correct valve-plate-to-body gasket must always be
selected in case of exchange. The gasket thickness is indicated on the gasket tab.
Each cylinder head has a plugged 1/8
” - 27 NPTF tapped hole for connecting high-pressure
switches. These high-pressure switches must be calibrated and tested before putting the
compressor into service. They must stop the compressor if the allowable pressure is exceeded.
The complete cylinder head is under discharge pressure.
2.6.2 Compressor cooling
Compressor motors must always be cooled, and cylinder head cooling may also be needed at
certain operating conditions.
K and L compressor motors can utilize air or water cooling. For air cooling, the airflow should be
at least 18.5 m³/hr. Note that the airflow also cools the cylinder heads. This airflow can come
from the fan of an air-cooled condenser or from a separate fan. Some high pressure ratio
conditions may require additional head cooling.
For water cooling, the water is led through a water coil wound round the motor section. Usually
the water coil is connected before the water-cooled condenser. With mains water, a single coil
“W” is used, and with cooling-tower connection a split coil “W2” is used. To improve heat
transmission, the water coil is embedded into thermocement on motors >0.75 HP but smaller
than 4 HP. If cylinder head cooling is also required, an additional fan must be installed with
water-cooled compressors.
All compressors starting with 2* until 8* are suction gas-cooled. With suction gas-cooled
compressors, the motor is cooled by refrigerant gas that is led over the motor. An additional fan
may be required depending upon the operating condition (see Copeland brand products Select
software).
NOTE:
For additional fan cooler mounting instructions, please refer to Technical
Information
D7.11.1 “Semi-hermetic compressors – Additional fans”.
NOTE:
R22 is no longer allowed for new refrigeration systems in Europe.
2.6.3 Unloaded start
With direct starting the motor of a compressor is switched directly into the mains by means of a
switch. The resulting breakaway starting current amounts to multiple times the rated motor
current (operating maximum) without consideration being given to transient phenomena.
In the case of high-powered motors the breakaway starting currents become so large that they
lead to disruptive voltage dips in the mains. The compressors that are subject to current
limitation must therefore by all means be equipped with starting load reduction to guarantee
