Regulation Of Reciprocating Compressors - Johnson Controls SABROE UniSAB III Engineering Manual

Compressor control and surveillance
3.1.8

Regulation of reciprocating compressors

Reciprocating compressors are capacity regulated in stages by connection/disconnection of cylinders,
typically in pairs, through solenoid valves controlled by UniSAB III.
How fast the compressor loads/unloads stages is determined by the timers Delay up and Delay down,
which will start counting as soon as the value is outside the neutral zone. The regulator is allowed to
have a P Band of 0, which means that the stages are loaded in seconds as set.
If the P band is above 0, the delay times can be prolonged as long as the value is within the P band. The
P band is only relevant if the P band factors Delay up and/or Delay down are set in the picture P band
factor at a value above 1. See P band factor in section 6.5 Timers.
If the value is just outside the neutral zone and the P band factor Delay up is e.g. 10, counting will be
slow: "1 sec." becomes 10 sec. If the value is just outside the P Band, counting will be speeded up, "1
sec." becomes 1 sec.
For reciprocating compressors connected to frequency converters see also the UniSAB III sequence
manual.
Engineering manual - UniSAB III 1.10.8
76/346 001930 en 2021.06