The case for fixed speed
A fixed speed screw compressor running at its design point has no drive losses and no speed-control electronics to maintain. When a plant genuinely consumes its full output for long periods, that simplicity shows up in both capital cost and reliability. The mistake is using one where demand swings, which is what variable speed exists to solve.
What the catalogue covers
Our fixed speed family spans 7.5 kW to 250 kW with free air delivery from 1.2 to 13.4 m3/min across the range, and pressures in the 7 to 12 bar band. Many models are supplied as integrated packages with receiver, dryer and filters on one frame.
Getting the control right
| Control mode | Behaviour | Best when |
|---|---|---|
| Load / unload | Runs loaded to the set pressure, then unloads and idles | Demand is close to capacity and storage is adequate |
| Modulation | Throttles inlet to match demand | Rarely the efficient choice at low demand |
| Start / stop | Stops when the receiver is full | Small systems with generous storage |
| Cascade | Two or more machines staged by pressure bands | Demand varies across a wide range |
Storage is part of the control
A fixed speed machine can only run in efficient blocks if there is somewhere for the air to go. A receiver sized for the cycling band turns a machine that would otherwise load and unload every few minutes into one that runs in long, stable blocks. This is why receiver sizing and compressor sizing belong in the same conversation.
Maintenance that prevents surprises
- Inlet valve - the part that cycles most; a worn valve leaks and the machine runs loaded when it should not.
- Oil separator - rising differential pressure means rising energy cost and eventual oil carryover.
- Cooler - dust on the cooler raises discharge temperature and shortens oil life.
- Drive belt or coupling - check alignment and tension at every service.
Browse the range on the fixed speed screw compressor collection page.
Tell us the working pressure, flow and site conditions and we will propose a configuration. Contact OPPAIR.