Variable speed drive (VSD) operation brings possibility to significantly reduce the flow & pressure ratio (and adsorbed power) for partial load operation & turndown. Depending on compressor OEM design, flow/pressure increases in range of several percent are also possible by increased operating speeds.

VSD should be considered especially for cases where old drivers are being replaced anyways. In most cases, no changes to compressor mechanical structure are required due to variable speed.

During VSD upgrades several aspects has to be considered – compressor thermodynamic performance, lateral & torsional rotordynamics. VSD frequency converters harmonics may interfere both mechanically with compressor and electrical with grid.

RotMach can provide know-how on all these aspects and coordinate projects with major electric drive OEMs like Siemens or ABB.


Existing compressors can be upgraded with inlet guide vanes (IGV). IGV extend operating range flexibility in terms of flow, significantly reduce adsorbed power during partial-load operation.

Variable IGV significantly extend operating range towards low flow with reduced pressure ratio. Compared to pressure throttling, the IGV can significantly improve the efficiency (adsorbed power) in off-design operating points.

IGV upgrades are typically suitable mainly for integrally geared compressors.


Replacing of aged electric motors with modern high efficiency motors can bring power savings in range of few percent.

In recent years some older gas turbines are increasingly difficult and expensive to maintain due to lack of OEM parts. Their replacements with VSD electric motors & frequency converters are often optimal solution. Return on investment is generally good, depending on site available electrical connections and machine utilization through year.

We can execute driver replacement projects with major electric drive OEMs like Siemens or ABB and ensure all necessary steps (API compliant VSD torsional analysis, lateral rotordynamics etc.) are provided. We can furnish detailed baseplate and auxiliary systems including lubrication & piping system designs.


Centrifugal compressor revamps/ rerates are typically revolving around impeller upgrades / modifications. On older compressors sometimes significant power savings can be achieved. Modern  impellers are precised by CAD/CAE methods and can be fitted to client gas specific parameters to deliver superior aerodynamic efficiencies.

Flow and pressure reductions are relatively straightforward, cost efficient and can provide substantial operating cost savings by adapting the compressor to current typical process parameters. In some cases, if original impellers are in good shape, they can be just adapted (machined) for required operating conditions, offering excellent cost/value ratio.

Depending on OEM compressor design margins, pressure and flow increases are also often possible in range of few percent.

We are prepared to support our clients from feasibility studies, where machine modification potential is evaluated, through detailed aero/mechanical design up to machine commissioning.


If an existing compressor is equipped with a vaneless diffusers, significant energy savings can be acheived by adding vanes to the diffuser. Vanded diffuser has considerably higher efficiency for the given flow, but typically also somewhat reduces usable flow control range.

If the compressor is operated on broader operating flow range, variable diffuser guide vanes (DGV) can be designed and added to the compressor control system. Variable DGV provide energy savings over extend flow operating range while keeping the pressure ratio close to constant.

Variable DGV upgrades are typically suitable for IGC compressors. On single shaft units tight design space renders DGV upgrades extremely difficult in most cases.