This site uses cookies which allow us to give you the best browsing experience possible. To find out more, please see our Privacy Policy.


EMA Electromechanical Linear Actuator

EMA Electromechanical Valve Actuator with Fail-safe Function, Linear Servo Electric Valve Actuator, Linear Actuator for Governor Valve Control with Trip Function, e.g. for Gas Turbine or Steam Turbine Applications

The EMA is an electromechanical linear actuator with trip function. It operates, for example, a valve that regulates the mass flow in a prime mover or a driven machine. Typical machines are gas turbines, steam turbines or compressors. The EMA provides you with highly dynamic and precise control of the mass flow.

This innovative linear actuator with fail-safe function has only electrical and mechanical interfaces. It is oil-free. This eliminates all costs for oil management that arise when operating a hydraulic linear actuator; an 80% lower energy consumption reduces operating costs even more. In addition, an oil-free actuator reduces the fire load of the entire system; insurance companies usually reward this with lower premiums. There is also nothing hindering the use of the actuator in places with strict environmental requirements.

With the EMA, you get an operationally safe and reliable plug-and-play solution having its own particular charm. The estimated mean time between failures (MTBF) of the Voith EMA is 35 years. As a result, your machine is very durable and you increase the productivity in your plant.

PS: Are you thinking about an oil-fee turbine? If you are, the EMA is certainly worth considering.


Voith Turbo GmbH & Co. KG
Electronic Drive Systems
Voithstr. 1
74564 Crailsheim, Germany

Tel. +49 7951 32-470
Fax +49 7951 32-605

Technical data

Closing time for full stroke (trip) Typically < 0.3 s
Motion time for full stroke (controlled) Typically 0.5 s
Spring force Up to 30 kN
Actuating force Up to 40 kN
Mean time between failures (MTBF) 35 years
Supply voltage for the EMA electronics 24 VDC
Current consumption for the EMA electronics 3.4 A
Supply voltage for the control unit 3 x 207 – 528 VAC, 50/60 Hz
Current consumption for the control unit 17 A, max. 32 A,
when balanced < 1 A
Input signal 4 - 20 mA
Communication (optional):
  • EtherCAT
  • CANopen
  • CANsync
  • Sercos
  • Others upon request
Fail Safe Operation Piston rod retracted or extended, depending on the design
Ambient temperature -20 to +80°C (standard version, not rated for use in potentially explosive areas)
Degree of protection IP 65
Safety integrity level SIL 2 (optional)
Optional Design as a trip actuator with no control function (switch actuator)

Typical Applications

  • Actuation of the control valve in
    • Steam turbines
    • Gas turbines
    • Compressors
  • Retrofit of mechanical-hydraulic valve controls
  • Retrofit of hydraulic, electromechanical and pneumatic actuators
  • Linear actuator for process valves with fail-safe function
  • Upgrading systems with the Voith DSG I/H converters, WSR way valves and SMR control servo motors
  • Upgrading systems with Woodward actuators:
    • PGPL Hydraulic Powered Electric Actuator
    • TM 25LP or TM 200LP Linear Proportional Actuators
    • CPC or CPC II Current to Pressure Converters

Advantages and Benefits

Features Advantages Benefits
  • Electromechanical design with synchronous motor and screw drive
  • The linear actuator is oil-free.
  • The actuator has only electrical and mechanical interfaces.
  • You save the procurement and maintenance costs required for an external hydraulic power pack with an oil tank and the pipework. Up to 35% of the procurement costs can be saved compared to a conventional system.
  • System integration is simple and economical.
  • Your entire system has high operational safety. Malfunctions such as those caused by contaminated pilot oil or by an oil leak just cannot happen.
  • The lower fire load increases your safety. This often reduces your insurance premiums.
  • The actuator is an optimal solution for new systems and for retrofits.
  • Commissioning is considerably simpler and is much faster than for hydraulic linear actuators. You save up to 5 days during commissioning because it is not necessary to flush and vent any pipes.
  • No knowledge of hydraulics is required for installation and commissioning.
  • The EMA is the ideal linear actuator for areas with stricter environmental regulations.
  • The design is low-wear and low-maintenance.
  • This will save maintenance costs for you.
  • Safety function is provided by a high-strength return spring and magnetic coupling.
  • The fail-safe function is achieved simply and safely.
  • The trip speed is fast, the trip time is typically < 300 ms
  • Your system has a high degree of operational reliability.
  • A reliable trip of the control valve reduces the danger of immediate and consequential damage.
  • The safety function (trip) and the operating function (control mode) are decoupled.
  • Trip is initiated by means of a separate safety control circuit.
  • Electromechanical position control with synchronous motor and threaded spindle.
  • No valves.
  • The linear actuator has a high level of energy efficiency.
  • You reduce energy costs for operating the actuator by up to 80% compared to an actuator using conventional valves and a hydraulic power pack.
  • With lower CO2 emissions, you play your part in protecting the environment.
  • Modular design with few components – compatible with existing hydraulic, electromechanical and pneumatic actuators.
  • The application flexibility is high.
  • Integration into your system is simple and the planning effort is minimal.
  • The actuator matches your application in price and function.
  • The EMA is a high-quality, cost-effective actuator solution for new systems, retrofits or modernization projects.
  • Constant control with the permanently excited synchronous motor.
  • The control system of the linear actuator operates with no response delay.
  • The actuator is ready to operate immediately, especially after a trip.
  • You have high system availability leading to higher productivity.
  • The valve actuator operates with virtually no hysteresis.
  • The control system is precise and highly dynamic.
  • Your processes are stable and product quality is high.

Technical information


1 Coupling
2 Synchronous motor
3 Junction box
4 Gearbox
5 Displacement transducer
6 Return spring
7 Piston rod


Control Schematic

How it works

The control system activates the EMA using a 4 – 20 mA standard signal. The stroke of the piston rod is proportional to this standard signal w. In the event of tripping, when the valve closes quickly, an electromagnetic coupling opens and decouples the motor mass. The return spring moves the piston rod into the safety position within 300 ms, either fully retracted or fully extended.

The EMA has two functions, namely providing a control mode and ensuring safety. In control mode, the EMA regulates the position of the piston rod using the setpoint w from the control system. The piston rod is connected to the control valve that controls the mass flow and changes its opening cross-section. If the setpoint signal is switched off (< 3.2 mA), the electromagnetic coupling opens. The piston rod is moved to the safety position by the energy stored in the return spring. This is carried out in an uncontrolled manner and at high speed. The piston rod is held in the safety position. Additionally, the power section of the VFD is switched off. This ensures that the piston rod moves to its safety position even in the event of an electromagnetic coupling malfunction.

An auxiliary electrical power supply is required for operating the EMA. All electrical components are protected against environmental influences. Electrical position detection is integrated in the drive. The controllers with circuitry for setpoint limitation and minimum value switch-off are integrated into the VFD. The control loop param­eters and the parameters for scaling the piston rod position are set on the VFD using the relevant software.