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Frequently Asked Questions
How does a screw compressor work?
Refrigerant is trapped between meshing helical rotors.
It is carried along and squeezed into less volume.
Compression is positive displacement.
A fixed volume moves per revolution.
It pushes against whatever pressure it meets.
Why is lift not a problem for these machines?
Positive displacement does not depend on gas velocity.
High condensing pressure raises the pressure ratio.
The machine takes it and keeps delivering.
Low evaporating temperature is handled the same way.
This suits hot climates and low-temperature process duty.
How far can a screw machine be unloaded?
A long way, without instability.
There is no aerodynamic limit at low flow.
Nothing corresponds to surge in a centrifugal machine.
That makes it tolerant of loads that move about.
Minimum capacity is set by the manufacturer, not physics.
How is capacity controlled?
Continuously, rather than in steps.
A slide valve varies the effective compression volume.
Variable-speed drive varies rotor speed as well.
Output follows the load smoothly.
Fixed increments are avoided altogether.
Why does part-load efficiency matter so much?
Because plant rarely runs at design load.
Most buildings spend most hours well below it.
Operating cost is decided in that region.
Smooth unloading is worth more than peak efficiency.
Full-load figures alone are misleading.
What does oil management involve?
Separation, cooling and monitoring of condition.
Oil travels with the refrigerant and must be recovered.
Separator performance affects heat exchanger duty.
Oil analysis gives early warning of wear.
It is a real part of owning the machine.
Where do screw machines sit against scroll and centrifugal?
Between them, overlapping both at the edges.
Scroll covers smaller duties with staged compressors.
Centrifugal covers the large tonnages.
Screw covers the middle and upper middle.
Conditions, not just tonnage, decide the overlap.