Page 306 - Compression Machinery for Oil and Gas

Screw Compressors Chapter 6 291

TABLE 6.2 Standard Instrumentation for Dry Screw Compressors

Trip
Suction Pressure Alarm Low Low
Suction pressure Alarm high in order to prevent Trip
overcompression or high high
torque
Discharge pressure Alarm high Trip
high
Suction temperature Alarm high Trip
high
Discharge temperature Alarm high Trip
high
Thrust bearing temperature Alarm high Trip
high
Journal bearing temperature Alarm high Trip
high
Casing vibration or shaft vibration Alarm high Trip
monitoring a high
Injection flow (if applicable, for Alarm low Trip
machines that have liquid injection in all low
specified operating conditions)
Lube oil pressure Alarm low Trip
low
Lube oil pressure Alarm high
Lube oil temperature Alarm high
Start-up interlock low

a
Due to the stiff casing design, 1 accelerometer per compressor or 1 accelerometer at each compressor
end (max 2 in total) is sufficient for automatic monitoring with shutdown.

enclosed O-ring. Dry screw compressors with vertical split and discharge pres-
sures of >5MPa have been built. Horizontal split casings generally have design
pressures up to 1.6MPa. However, it is important to note that in many cases the
compressor may not be able to operate at the maximum discharge pressure of
the casing due to other limitations.
The maximum discharge pressure must be clearly distinguished from the
maximum allowable differential pressure. The maximum allowable differential
pressure depends on the rotor profile, lobe numbers, L/D, shaft diameters, and
bearing design and size. The maximum allowable differential pressure is often
much less than the maximum discharge pressure. For example, even if the