Engineering manual - SAB 355 Screw compressor unit (including ATEX)
004100 en 2020.10
67/156
Technical description
the economiser port, which could result in motor overload. Example: A system feeding liquid to
the flash vessel in batches.
The recommended economiser systems are shown below. Notice that in all systems there should
be a strainer (STR) and a check valve (CV) between the economiser vessel and the economiser
port on the compressor. The strainer prevents dirt from passing into the compressor, and the
check valve prevents oil from flowing from the compressor unit to the economiser vessel during
shutdown.
Caution!
It is recommended to use piston-type check valves for installation in the economiser line, as op-
posed to disc-type check valves. The latter are more prone to gas pulsation-induced failure. The
isolation and check valves as well as the strainer should be located as closely as possible to the
compressor, preferably within 1 metre.
Anti-vibration kit
For SGC compressors running ammonia at high suction temperature and variable frequency drive
(VSD), an anti-vibration kit should be installed on the economiser line. The anti-vibration kit con-
sists of a strainer, a stop valve, a check valve and a damper (pos. 208). The damper should be in-
stalled as the last device before the compressor.
Fig. 45: Standard economiser kit
Fig. 46: Anti-vibration economiser kit
Fig. 47: Anti-vibration Economiser kit
For refrigeration plants employing multiple compressors on a common economising vessel, re-
gardless of economiser type, each compressor must have a back-pressure regulating valve in or-
der to balance the economiser load, or gas flow, between compressors. The problem of balancing
load becomes most important when one or more compressors run at partial load, exposing the
economiser port to suction pressure. In the case of a flash vessel, there is no need for the redun-
dancy of a back-pressure regulating valve on the vessel and each of the multiple compressors.
Omit the BPR valve on the flash economiser vessel and use one on each compressor, as shown in
Fig. 50. It is also recommended that the back-pressure regulating valves, used on economiser
lines, should be specified with electric shutoff option. The electric shutoff feature is necessary to
Economiser kit
optional
Strainer
S
hipped loose
Damper
with str
ainer
Ec
o. line
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