Table 16: Valve position during operation, oil pump (optional)
Position number
Designation
In-operation position
145
Service valve - oil pump
Closed
149
Stop valve before oil pump
Open
Table 17: Valve position during operation, liquid injection (optional), single port
Position number
Designation
In-operation position
165
Liquid stop valve
Closed
170
Stop valve before oil pump
Open
Descriptions of main components and systems
The screw compressor unit is an integrated system consisting of the following major subsystems:
• Control system
• Compressor
• Compressor lubrication system
• Compressor oil separation system
• Compressor hydraulic system
• Compressor oil cooling system
• Compressor easy-start system
The information in this section of the manual provides the logical step-by-step instructions to
properly start up and operate the screw compressor unit.
You must read the following subsections and understand them before you attempt to start or
operate the unit.
Compressor
The rotary screw compressor uses mating asymmetrical profile helical rotors to provide a
continuous flow of refrigerant vapour, and it is designed for both high-pressure and low-pressure
applications. The compressor incorporates the following features:
• High capacity roller bearings to carry radial loads at both the inlet and outlet ends of the
compressor.
• Heavy-duty, four-point contact ball (SG_B-models) or angular contact bearings (SG_H-models) to
carry axial loads are mounted at the discharge end of compressor.
• Balance pistons located in the inlet end of the compressor to reduce axial loads on the axial
load bearings and increase the bearing life.
• Movable slide valve to provide fully modulating capacity control from 100% to approximately
10% (3519 to 15%; 3524 to 20%) of full load capacity.
• VI volume ratio control to allow infinitely variable volume ratio from 2.2 to 5.0 during
compressor operation for most models.
- SGC 2824, VI: 2.0 to 4.1
- SGX 3519, VI: 2.2 to 4.5
- SGX 3524, VI 2.4 to 4.5
• A hydraulic unloader cylinder to operate the slide stop and slide valve.
• Bearing and casing design for 28 bar [400 psi] discharge pressure.
45
SAB 283-355 A-Frame OHU 6042 and OHU 7650 (including ATEX) Screw Compressor Unit
