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Variable Speed Fluid Couplings

With more than 15 000 units in use, the Voith variable speed fluid coupling re­presents one of the best documented options for controlling the speed of driven machines. These units generally have a service life of several decades. They can be deployed in areas ranging from high-efficiency gas and steam combined cycle power plants, to refineries and the highly demanding oil platform environment, as well as numerous fan applications. The hydrodynamic principle coupled with a simple structure give these variable speed fluid couplings the high reliability needed to excel under virtually any conceiv­able environmental conditions. In the power range from 100 kW to 10,000 kW and with input speeds up to 3,600 rpm, they enable cost effective, precise and step­less control of the speed of the driven machine. An adjustable scoop tube steplessly varies the coupling filling during operation. The coupling filling determines the power transmitted and consequently the speed of the driven machine. This type of speed control is simple, dynamic and reliable. The speed setpoint parameter uses a 4 – 20 mA standard signal. The integration of a Variable Speed Fluid Coupling into the drive train increases the productivity of your machine or plant.

Are you planning a project with a variable speed drive in the power range 0.1 to 10 MW?
Then contact us. We can look for the best solution together.


Voith Turbo GmbH & Co. KG
Variable Speed Drives (aev)
Voithstr. 1
74564 Crailsheim, Germany

Tel. +49 7951 32-261
Fax +49 7951 32-650


Service, Spare Parts, Repair
Tel. +49 7951 32-1666
Fax +49 7951 32-903

Service Helpline (24/7)
Tel. +49 7951 32-1616

Technical data

Power 100 – 10,000 kW
  • Horizontal
  • Vertical
  • Cast iron housing
  • Welded housing
  • Antifriction bearings
  • Sleeve bearings
Motor speeds Suitable for all standard motor speeds

Advantages and benefits

  • We have been building variable-speed fluid couplings since 1952. They can be used almost anywhere – regardless of whether the climate is arctic, tropical or desert. A special version is available for potentially explosive atmospheres. Thanks to its compact, robust design, the variable speed coupling offers max­imum protection against external factors. This increases the reliability of
    your machine or system.
  • The drive motor power consumption at low speeds is less than for fixed-speed units with throttle control. That saves energy and reduces operating costs.
  • Wear-free hydrodynamic power transmission keeps maintenance costs low by allowing long intervals between scheduled maintenance tasks. Unlike electronic variable speed drive systems, no additional investments are needed over the entire lifetime.
  • Load-free motor start-up and smooth acceleration of the driven machine reduce the overall load on the driveline. The hydrodynamic variable speed coupling also dampens torsional vibrations and torque shocks, protecting the motor and the driven machine. This extends the service life of both, the drive and the driven machine.
  • The lube oil system on Voith variable speed couplings can supply oil to the motor and driven machine at any time. You save space and money.

Typical applications

Power generation

  • Boiler feed pumps
  • Fan drives
  • Cooling and condensate pumps

 Oil & Gas

  • Pipeline pumps
  • Crude oil pumps

Technical information

Design and function

  • Voith variable speed couplings are fluid couplings. They link the prime mover – generally an electric motor – with the corresponding driven machine.
  • The kinetic energy of the working fluid transfers the power. This fluid flows in an enclosed working chamber between the pump wheel (linked to the input shaft) and the turbine wheel (linked to the output shaft).
  • During operation the coupling fill level can be adjusted between 0% and 100% via the scoop tube. This makes it possible to control the speed of the driven machine in a precise, stepless manner.
  • The control range depends on the load characteristic (torque to speed ratio).

1 Pump wheel
2 Turbine wheel
3 Shell
4 Scoop tube housing
5 Scoop tube
6 Cooler
7 Oil pump
8 Oil tank

3D Sectional drawing