Engineering manual - SAB 355 Screw compressor unit (including ATEX)
004100 en 2020.10
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Technical description
4.1.19 Balance piston pressure regulator
A balance piston pressure regulator is required on some models (496-1080 (355)) to reduce the
extended overbalance from the thrust balance piston at part load.
High-stage SB-2 oil supply line diagram, Fig. 31 shows the three additions described below
arranged in parallel.
Pressure-regulating valve: Discharge pressure determines compressor thrust balance. The
proper setting for the pressure-regulating valve is 3.5 bar [50 psi] below DISCHARGE pressure.
Solenoid valve: Energizing, or opening, the solenoid valve pressurises the balance piston with
full oil pressure from the oil manifold, by-passing the A4ALE pressure regulating valve. De-ener-
gizing, or closing, the solenoid valve pressurises the balance piston with oil pressure regulated by
the A4ALE pressure regulating valve.
Signals from the control panel operate the solenoid valve (output module 12 on micro panel). The
solenoid valve should open when the slide valve position is 70% or greater, and close when the
slide valve position is 65% or less.
Orifice: The orifice ensures oil supply to the inlet end bearings during upset conditions such as
start-up.
Fig. 31: High-stage SB-2 oil supply line diagram
(only for SGCH 355) H = High pressure
From compressor
discharge or oil
manifold
Pressure-regulating valve
From oil manifold
Solenoid valve
To SB-2 compressor port
Restriction orifice (pipe)
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