HSO 2024 to HSO 2035 Installation, Operation and Maintenance Manual
Issue 1.2 : 03/10
Publication 2-119
Page 33 of 94
Positioning the oil injection ports in the capacity control slide valves
ensures that, at all slide valve positions, oil enters the main rotor flutes
after the flute volume has been sealed, i.e. oil injection always occurs
during the compression process over the whole capacity control range,
thus ensuring maximum pumping efficiency. Because oil is injected over
a period in the compression process when the pressure of the gas
trapped in the flutes is considerably lower than discharge pressure, this
means that in the majority of instances the system pressure difference
can be used to provide the required oil flow without the need for an oil
pump running continuously while the plant is in operation; refer to 7. Oil
Circulation.
Compressor cooling can be accomplished by the direct injection of liquid
refrigerant into the compression process. When liquid injection is not
used, the oil injected for sealing absorbs a large proportion of the heat of
compression, thus reducing the maximum discharge temperature, and is
cooled externally via an oil cooler; refer to 7.4. Compressor Cooling.