Operating manual- SAB 355 (including ATEX)
004059 en 2019.11
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6.12
Compressor hydraulic system
The compressor hydraulic system moves the movable slide valve (MSV) to load and unload the
compressor. It also moves the movable slide stop (MSS) to increase or decrease the compressor’s
volume ratio (Vi).
The hydraulic cylinder located at the inlet end of the SGC compressor serves a dual purpose. It is
separated by a fixed bulkhead into two sections. The movable slide valve (MSV) section is to the
left of the bulkhead and the movable slide stop (MSS) to the right. Both sections are considered
double-acting hydraulic cylinders as oil pressure moves the pistons in either direction.
Both sections are controlled by double-acting, four-way solenoid valves which are actuated when
a signal from the appropriate microprocessor output energizes the solenoid valve. Valves V1, V2,
SC1 and SC3 are always open.
Fig. 20: Compressor hydraulic system
Single-acting mode, high-stage
•
Close the valve at SC2
•
Open the valve at BP (by-pass)
High-stage compressor loading
The compressor loads when the MSV solenoid valve, YY2, is energised, and oil flows from the un-
loading side of the cylinder out of the port, SC1, through the valve ports, A and T, to the compres-
sor suction side. Simultaneously, the discharge pressure loads the slide valve.
High-stage compressor unloading
The compressor unloads when the MSV solenoid valve, YY1, is energised, and oil flows from the
oil manifold through the valve ports, P and A, to the cylinder port, SC1, and enters the unloading
side of the cylinder. Simultaneously, gas on the loading side of the cylinder is vented through the
port, SC2, and the valve, BP, to the compressor suction side.
Note:
To control the rate of loading and unloading, change cycle time, proportional band and
dead band setpoints with the control system. If additional control is needed, throttle SC2 or BP.
Double-acting mode, booster
•
Open the valve at SC2
•
Close the valve at BP (by-pass)
Valve 2
SC3
SC2
SC1
SC1
SC2
SC3
SC4
YY1
YY2
YY3
YY4
BP
sv-3
sv-2
P
T
Valve 1
SC4
BP
SC2
SC3
SC1
A B
P
T
T
P
B
A
1
1
2
2
1
2
1
2
Direction
control
valve
Screw in flow
regulating
needle valve
SC4 Not used
Direction
control valve
Hydraulic schematic
sizes 493, 676, 856, 1080
Compressor top view
YY4 (Decrease Vi)
YY2 (Load)
(Increase Vi) YY3
(Unload) YY1