Crankcase pressure = suction pressure for both
single- and two-stage compressors
In order to prevent excessive discharge pressures
in the compressor, one or more overflow safety
valves (number depends on the type of
compressor) are provided. These valves act on the
difference between suction and discharge
pressure and moreover, in the case of two-stage
compressors, between suction and intermediate
pressure.
The spring-loaded overflow safety valves are
adjusted at the works; they blow the gas off to
suction when there is an excessive pressure
difference.
The overflow safety valves are fitted externally
between the suction manifold and the HP and/or
LP discharge manifold.
4.9 OIL PUMP, FILTERS AND CONTROL OIL
SYSTEM (see fig. 4.5)
The oil pump is fitted on the bearing cover
opposite the compressor driving end and is
directly driven by the crankshaft.
The pump housing accomodates a double gear
pump consisting of three gears with the centre
gear driven by the crankshaft.
The oil suction and oil discharge filters are fitted
to the pump. The oil suction filter contains a metal
gauze filter element; the oil discharge filter is
provided with a paper filter element retaining the
fine (metal) particles suspended in the oil.
The oil is drawn from the crankcase via the oil
suction filter. The pressures dilevered by the gear
pump are a lubricating pressure and a control
pressure to operate the valvelifting mechanisms
(capacity control). The pressurized lubricating oil is
delivered to the discharge filter, led back to the
pump housing and into the lubricating system via
the crankshaft. The lubricating oil pressure
depends on the setting of the lubricating oil
pressure regulator built into the lubrication system
of the compressor (see also par. 4.10, Lubrication
system). The control oil pressure delivered by the
pump is regulated by a built-in relief valve
connected to the lubrication system. Excess of
control oil is thus used for lubrication. The control
pressure has been set at 13 - 15 bar above suction
pressure.
FIG. 4.5 OIL PUMP, FILTERS AND CONTROL OIL SYSTEM
1. Oil suction filter
2. Oil discharge filter
3. Relief valve
4. Gear pump
5. Hydraulic time delay
valve
A
To lubrication system via crankshaft
B
Control oil pressure to valve lifting mechanisms
for unloaded starting and capacity control
C
Oil suction from crankcase
Refrigeration Division
Grasso
4. GENERAL DESCRIPTION THE COMPRESSOR
v002.97.10.en
Refrigeration Compressors Series RC9
Page 4.5
