At a glance
- Type
- Oil-lubricated screw
- Architecture
- Single-stage screw
- Drive
- Permanent-magnet VFD
- Pressure options
- 8 / 10 / 13 bar(g)
- Power range
- 7.5–250 kW
Overview
SILVERLUBE-VPM is the variable-speed form of the SILVERLUBE S airend. A permanent-magnet motor runs through a frequency converter, so rotor speed — and therefore the air delivered — is set by what the plant is drawing at that moment rather than by a single fixed speed. It is the version to look at when the demand line is not flat.
Model range
Variable-speed models span 7.5–250 kW across three pressure rows: 8, 10 and 13 bar(g). Delivery at a given pressure belongs to the individual model, so read the row you intend to buy.
Speed
Set by demand
- Motor
- Permanent magnet
- Control
- Frequency converter
- Effect
- Output follows the draw
Pressure
8 / 10 / 13 bar(g)
- Range
- 7.5–250 kW
- Architecture
- Single-stage screw
- Selection
- By duty point and hours
Where it fits
A moving load
- Good fit
- Shift-varying plant air
- Poor fit
- Demand pinned at full output
- Decides it
- The load profile, not the nameplate
Technology
What changes with a VFD
Speed becomes the control variable. To hold network pressure the converter slows the rotor when demand eases and speeds it up when demand rises, so the machine produces roughly the air being used instead of repeatedly loading and unloading around a fixed output.
Why part load is the whole argument
A fixed-speed machine holds pressure by unloading, and while unloaded the motor still turns — drawing on the order of a quarter to a third of full-load power while making no air. That band is what a variable-speed drive removes, and it is why the comparison only makes sense against a real load profile.
Where the gain is biggest
Two conditions push the balance towards variable speed: a demand line that moves a lot, and long annual running hours that multiply whatever is saved per hour. A machine that genuinely sits at full output all year has little to gain from speed control.
More technical detail
Category benchmark
As an industry figure, variable-speed drive is commonly quoted at 20–40% lower energy than fixed-speed under fluctuating load. That is a category range, not a commitment for a particular model: the real number depends on the load profile, the annual hours and the pressure set point.
Setting the pressure
Variable speed does not remove the value of a correct pressure band. Lower the set point to the lowest value that still serves the furthest consumer and the saving compounds with the drive benefit.
Selection & quote checklist
- a load profile, or at least the consumer list and shift pattern
- annual running hours
- the lowest pressure set point the plant can hold
- whether the machine will trim or carry base load
- electrical supply and converter requirements
- the current datasheet and package contents
Applications
Shift-varying plant air
A metalworking shop where tools and valves run in bursts and the draw drops after the day shift.
Trim machine in a station
One variable-speed unit takes the swings while larger machines hold base load.
Weekend and night turndown
Where production slows but never stops, the machine keeps making only what is being used.
Processes with seasonal load
Demand that changes with order book rather than with the clock, so the peak-to-trough gap is wide.
FAQ
How much does variable speed actually save?
It depends on the load profile, the hours and the pressure set point. The category figure is 20–40% against fixed speed under fluctuating load; a project-specific estimate needs the consumer list and shift pattern.
Is variable speed worth it if the machine runs flat out?
Not usually. If demand sits at the machine’s rated output for most hours, there is little for speed control to do and the fixed-speed page is the better comparison.
Does the drive change the air treatment behind it?
No. Drying and filtration follow the process air-quality requirement, which the drive does not alter.
Why a permanent-magnet motor?
The permanent-magnet rotor is what the variable-speed line is built around; it is the motor type used across these models rather than a separate option.
The savings figures are category references until calculated against your own load profile.
