3. DESCRIPTION AND OPERATION OF THE
COMPRESSOR PACKAGE
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3.1 PRINCIPLE OF OPERATION OF TME COMPRESSOR
PACKAGE
Since �orrect operation of the compressor largely depends
on the mjection of sufficient oil quantities, the functional
method of operation of the package can be
divided
into two
separate systems: the (refrigerant) gas system and the oil
system. Refer to the basic flow diagrams in figure
3.�.
The (refrigerant) gas system
The gas drawn trom the evaporator enters the compressor
package via an inlet device consisting of a suctïon stop
valve,
a
suction check valve and
a
suction gas slrainer
,
which is mounted on top of the compressor.
After compressfon, the mixture of discharge gas and in
jected oil is fed into an oil separator, in which the oil is
separated trom the gas and collected. From the oil separ
ator the discharge gas leaves the compressor package to
the condenser via
a
dlscharge check valve and
a
discharge
stop valve. The separated oil continuates its way to an oil
cooler in preparation
tor
re-injection.
The discharge check valve prevents high pressure gas or
liquid from the condenser
trom
entering the oîl separator
during shu
i
-down
.
The suction check valve prevents high
pressure gas trom escaping trom the oil separator via the
compressor
to
the evaporator, thus reducing back-spin of
the compressor after stopping. However, the tatter phe
nomenon may nevertheless occur, depending on the
gas
volume present between check valve and compressor inlet.
In that case a by-pass line, provided with a normally closed
by-pass valve, will be frtted between the compressor suction
line and the oil separator (not indicated in fig. 3.1 ). This by
pass valve opens
as
soon as the package is stopped, so
that high pressure gas can flow to the suction side in order
to quickly eliminate the pressure dlfference aaoss the com
pressor.
The oil system (also refer to paragraph 2.7)
From the oit separator the oil, of which the temperature is
lower than and the pressure is equal to those of the dJS
charge gas, flows via an oil cooler and a straîner to an oil
distribution line. From there the oil is fed to the compressor
tor injection into the female rotor grooves, to the balance pis
ton and to the electrically driven lubrication oil pump. This
pump delivers, via a generously main flow oil filter, the oil
for the lubrication of shafl seal and bearings and
tor
the h.J
brication/positioning of the capacity control slide valve.
The excess of the oil pump capacity is returned trom the oil
discharge manifold to the oil separator via an overflow relief
valve to regulate the lubrfcating
(=
pump) pressure.
The oil line for injection into the rnale rotor grooves is bran
ched trom the top of the oil cooler shelL
Only if the difference between condensing and evaporating
pressure (= 6p) is smaller than 1.5 bar, a full-flow (electrîc
motor driven) oil pump is necessary.
For this aJtemative oil system, wnlch is only applled under
certain booster conditions, refer to the bottom picture of tig
ure 3.1_
3.2 DESIGN DETAILS OF THE COMPRESSOR PACKAGE
The detailed lay-out and flow diagram oi the standard com
pressor package is shown in figures 3.2 to 3.5, of which the
figures 3.2 /3.3 and 3.4/3.S correspond respectively
with
the
basic refrigerant and oil flow diagrams as described in para.
3.
1. The only difference between the figures
3.2
and 3.3
and between 3.4 and 3.5 is the method of oH cooling ap
plied.
According to these flow diagrams the following main parts
of the standard package can be distinguished:
- A standard Grassoscrew compressor GSL (1 ), complete
w1th electric drive motor
(2)
and flexible coupling
(3)
with
coupling guard (4). For a detailed description of the com
pressor refer to Chapter 2.
-
A servo-motor operated capacity control (EVA, 5)
mounted onto the hydraulic cyl1nder of the compressor.
Refer to para. 3.4
tor
detailed information.
- An inlet device, consisting of a suction stop valve (27),
check valve (26) and strainer (25, filtrating rating 100
microns). incorporated i11 one single housing. which is
mounted on top of the compressor on the suction connec
tion.
A small diameter bypass line (blow-down line
24)
with
stop valve, fitted across this device, allows the package to
be de-pressurized by hand, if needed.
• A vertical (primary) oil separator (7), complete with a
spring-loaded pressure safety valve (8), an oil level sight
glass (9) and a500 W heat,ng element (10). In certain
cases a secondary oil separator (100) may have been in
stalled on request of the installer or contractor. For a de
scriptlon of the oil separators refer to para.
3.3.
- A water cooled or refrigerant liquid cooled "shell and tube·
type oil cooler (18b and 18a respectively) in which the
water or retrigerant flows through the tubes and the oil
through the shell around the tubes, guided by a number of
baffles.
From the top of the oil cooler shell the oil line tor degass
ing and injectlon into the male rotor grooves is branched_
In case of water coollng (fig. 3.3 and 3.5) a water flow
regulating vaJve (19b), controlled by the oil temperature in
the oil discharge manifold (21b) may have been provided.
In case of refrigerant liquid cooling (fig. 32 and 3.4) the
oil outlet line may have been provided with a three-way
regulating valve (19a, also controlled by the temperature
in the oîl discharge manlfold), combined with a bypass
line to the oil inlet line.
- A
main flow oil filter
(20)
with pressure drop sensing
switch (20a). The filter consists of à cyllndncal housing
with cover, in which a removable synthetic fibre filter (10
-
15
microns) is mounted. The pre
s
sure
drop
(differential
pressure) sensing switch activates a waming signa! as
soon as the pressure drop across the filter element, due
to pollution, beoomes exoessive.
- A lubricating oil pressure regulator (11 ), mounted onto the
(primary) oil separator, and which allows the oil to pass at
a certain pressure only, thus determining the pressure in
the lubricating system.
92.01
Compressor Package GSLP
Page3.1
