Operating manual- SAB 355 (including ATEX)
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004059 en 2019.11
Operating instructions
separator takes more than 20-30 minutes to equalise to suction pressure after shutdown, NV-2
can be opened slightly. See Fig. 22.
Fig. 22: Suction check valve by-pass
Check valve CV-4 is installed on all units with suction pressure below atmospheric or installed with
economiser option utilised on multiple compressor plants.
On high-stage systems, the check valve, CV-4, should be installed with a 3.1 bar [45 psi] spring
to avoid the possibility of back-feeding to a shutdown compressor from a common economiser
vessel.
On booster systems, the check valve, CV-4, should be installed with a 1.7 bar [25 psi] spring to
avoid the possibility of air ingress into the system if the system suction pressure is below
atmospheric.
NV-2 must be closed if the oil pump should run for long periods of time when the compressor is
stopped. This is important in order to avoid oil being pumped up the suction line.
6.18 Balance piston pressure regulator
A balance piston pressure regulator is required on some models (496-1080 (355 H) to reduce the
extended overbalance from the thrust balance piston at part load.
High-stage SB-2 oil supply line diagram - the diagram 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-
gising, 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.
From
separator
cold-start
valve
For 8” and larger suction valve
customer supplied line
Compressor end view
Suction gas
to the compr.
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