Control System - LG RCAW Operation & Maintenance Manual

Service
Number Description
1 Compressor casing
2 Motor casing
3 Oil separator
4 Motor rotor assembly
5 Motor stator assembly
6 Motor rotor washer
7 Motor rotor spacer ring
8 Oil separator baffle
9 Oil separator cartridge
10 Piston
11 Piston spring
12 Piston rod
13 Bearing seatÅfs cover plate
14 Modulation solenoid valve
15 Modulation slide valve
16 Slide valve key
17 Discharge bearings
As shown in the below, during rotation of the rotors the meshing shifts from the suction side to the discharge
side. The meshing rotors enclose a working space, which is continuously reduced as it moves in the axial direc-
tion. This causes a V-shaped lobe space to form between each of the male and female lobes. This lobe space
increases to a maximum size (suction and sealing process). As the rotors rotate further, the new meshing on
the suction side closes the V-shaped lobe space. The lobe space is then constantly reduced by continuing inter-
meshing of the lobes (compression process).
The reduction in lobe space takes place on the lower side of the rotors towards the discharge side. The volume
is steadily reduced and it is thereby compressed in the sealed condition. As soon as the peaks of the rotor teeth
are free to the outlet port, the vapor is discharge to the high-pressure side and flows to the oil separator where
the high-pressure gas will be separated from the lubrication oil. The size and geometry of the discharge port
determine the so called "internal volume ratio (Vi)" of the compressor. This ratio must have a defined relation-
ship to operating pressure ratio to avoid losses in efficiency due to under or over compression.
The screw compressor is equipped with 4-step capacity control system. The capacity control system is consist-
ing of a modulation slide valve, piston rod, cylinder, piston and piston rings. The slide valve and the piston are
connected by a piston rod. The principle of operation is using the oil pressure to drive the piston in the cylinder.
The positive pressure differential causes the piston to move toward the right side in the cylinder. When the slide
valve moves toward the right side, the effective compression volume in the compression chamber increases.
44 Chiller Air-cooled Screw
Number Description
18 Discharge fixed ring
19 Disc spring
20 Bearing lock nut
21 Male rotor
22 Suction bearings
23 Suction bearings inner/outer spacer ring
24 Oil guiding ring
25 Suction filter
26 Oil heater
27 Refrigeration Lubricant
28 Suction flange
29 Discharge flange
30 Cable box
31 Power bolt
32 Thermostat terminals
33 Motor cable cover plate
34 Discharge check valve
Table 14
Fig. 22