At a glance
- Type
- Oil-lubricated screw
- Architecture
- Single-stage screw
- Drive
- Fixed-speed, direct coupled
- Pressure options
- 8 / 10 / 13 bar(g)
- Power range
- 7.5–250 kW
Overview
SILVERLUBE Fixed-Speed is the same single-stage oil-injected airend, driven at one speed by a motor coupled straight to it. Network pressure is held by loading and unloading: as demand falls the inlet closes and the motor keeps turning at reduced load. It carries the lowest purchase cost of the SILVERLUBE S drive options and is built for plants whose air draw is steady.
Model range
Fixed-speed models cover 7.5–250 kW at 8, 10 and 13 bar(g). Each pressure row has its own delivery figures — take them from the datasheet row, not from the power rating.
Drive
One speed, direct coupled
- Between
- Supply and rotor: a coupling
- Not fitted
- No frequency converter
- Consequence
- Fewest components in the train
Control
Load and unload
- Demand falls
- Inlet closes, motor idles
- Unload draw
- Roughly a quarter to a third of full load
- Design aim
- Keep unload time short
Where it fits
A steady draw
- Good fit
- Continuous, near-full-output demand
- Poor fit
- A demand line that swings widely
- Decides it
- Hours spent in unload
Technology
What the direct drive leaves out
There is no converter between the supply and the rotor, so there is nothing to programme, nothing to tune and one less item on the service list. For a plant that wants the air room to look after itself, that simplicity is the point.
How pressure is held
The machine runs at its rated speed. When the receiver reaches the upper set point the inlet valve closes and the machine unloads; when pressure falls it loads again. The air is made in full-output steps, which is why the fraction of the shift spent unloaded is the number that decides the energy bill.
When this beats variable speed
Three conditions: a draw that stays close to rated capacity; production that is continuous enough for unload time to be small; and a purchase budget that matters more than converting energy. Under those conditions the lower purchase price and the smaller parts inventory carry the decision.
More technical detail
The honest comparison
Both machines sit in the same 7.5–250 kW, 8/10/13 bar envelope; the difference is how each meets a falling load. Fixed speed steps between full output and unloaded running. Variable speed slides continuously. If the site’s draw is steady, the steps are rare and the cheaper drive wins on total cost.
What to measure first
Estimate the share of running hours the machine will spend unloaded, using the consumer list and shift pattern. That single estimate tells you whether fixed speed is comfortable here or whether the variable-speed page deserves the comparison.
Selection & quote checklist
- how steady the air draw is across the shift
- the share of hours likely spent unloaded
- base load versus trim duty in the station
- receiver volume, which shortens unload cycling
- whether a rotation controller will sequence several units
- the current datasheet and package contents
Applications
Continuous production
A process that runs through the shift at a settled draw, where the machine rarely leaves full output.
Base-load machine in a bank
Two or three units share the load and rotate under a controller; each runs near capacity while it is on.
Two-shift fabrication
Tools and cutting equipment running both shifts with little change in the air drawn.
Plants with limited maintenance resource
Where the priority is a drive train with the fewest parts to service rather than the last percent of efficiency.
FAQ
Fixed speed or variable speed?
Measure how steady the draw is. A demand line that stays near rated output suits the cheaper fixed-speed drive; one that swings widely is where variable speed earns its price.
What happens to the energy bill during unload?
The machine keeps turning while making no air, drawing roughly a quarter to a third of its full-load power. Ample receiver volume and a well-set pressure band both reduce how often that happens.
Can several fixed-speed units run together?
Yes, and it is a common arrangement: a number of machines in parallel with receivers and a rotation controller that shares running hours between them.
Is anything lost by not having a converter?
Only the ability to follow a falling load smoothly. Everything else — the airend, the air quality, the pressure band it can serve — is the same as the variable-speed models.
Confirm the model row, FAD and package contents on the current datasheet.
