HSO 2024 to HSO 2035 Installation, Operation and Maintenance Manual
Issue 1.2 : 03/10
Publication 2-119
Page 37 of 94
7.
Oil Circulation
An oil circulation pump can be dispensed with for most operating
conditions using HSO 2000 series compressors or if a pump is necessary
it is only required to run at start-up.
For applications without an oil pump, oil circulation is maintained by the
pressure difference generated between the high pressure side of the
system and the pressure in the sealed main rotor flute at the point of oil
injection. When the compressor stops, a special, fail-safe solenoid valve
arrangement (refer to Fig 3) automatically returns the capacity control
slide valves to minimum load.
For applications using an oil pump for starting only, the pump is used to
provide adequate lubrication for the bearings and mainshaft gland seal,
and an oil pressure source to return the compressor capacity control slide
valves to the minimum load position prior to starting. After a short period
the pump is stopped and oil injection maintained by the system pressure
difference. Non-return valves are positioned in the oil lines to ensure that
oil is only delivered to the lubrication and capacity control connections
when the pump is running. When self-injection takes over, oil is fed to
the lubrication, capacity control and oil injection connections.
Exceptions to the above occur when there is only a small system
pressure difference. Typical examples are under low ambient conditions,
low load operation and most low stage (booster) applications. If the
difference between absolute discharge pressure, measured at the outlet
from the oil separator, and twice the absolute suction pressure is less
than 2 bar abs, pumped oil injection/lubrication is necessary using a full-
flow oil pump running continuously while the compressor is operating.
For minimum pumping capacities refer to Table 3.
HallScrew
Compressor
Pumping
Capacity m
3
/hr
HallScrew
Compressor
Pumping
Capacity m
3
/hr
HSO 2024
4 to 6
HSO 2031
7 to 10
HSO 2028
5.5 to 8
HSO 2035
10 to 15
Table 3 Pumping Capacities For Continuously Running Oil Pump
Oil support systems, similar to those fitted to J & E Hall International
package units fitted with the HallScrew 2000 series compressor, are
illustrated in Appendix 2 Oil Support System Schematic Flow Diagrams.
All necessary valves, controls and instrumentation are shown in the
diagrams.
7.1.
Oil Differential Pressure Monitoring
As already discussed in 7. Oil Circulation, there are four basic oil support
systems depending on whether an oil pump is fitted and its behaviour.
•
No oil pump, system suction/discharge pressure differential
is high enough to maintain oil follow.
•
Start-up oil pump, runs to lubricate the gland and bearings
before the compressor starts, then stops. When the
compressor starts, system suction/discharge pressure
differential is high enough to maintain oil flow.
•
Continuously running oil pump, for low system pressure
difference applications, starts and stops with the
compressor.
•
Demand oil pump, combines features of a start-up and a
continuously running oil pump.
