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SelCon Linear Actuator for Actuating Valve Control Equipment

SelCon Self-contained Electrohydraulic Linear Actuator with Fail-safe Function, Linear Servo Hydraulic Valve Actuator, Linear Actuator for Governor Valve Control with Trip Function, e.g. for Gas Turbine or Steam Turbine Applications

The SelCon is a self-contained, electrohydraulic linear actuator with a spring-assisted 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 SelCon provides you with highly dynamic and precise control of the mass flow.

This innovative actuator is a reliable plug-and-play solution with fail-safe function. The SelCon is a compact design, provides high force density and is a true alternative to conventional actuators. With the SelCon you don't need an additional hydraulic power pack with an oil tank, control block and pipework. The amount of hydraulic fluid in the system is minimal. On the outside the SelCon only has electrical and mechanical interfaces. Handling and system integration is extremely simple. No knowledge of hydraulics is required for installation and commissioning.

Our engineers selected proven components when designing the SelCon. The core components consist of a servo motor, a Voith internal gear pump, a cylinder with an internal return spring and a displace­ment transducer. A control unit with implemented application software acts as the brain of the system. The actuator exhibits a high degree of operational safety and reliability; the estimated mean time between failures (MTBF) is 35 years.

The SelCon is optionally available as a trip actuator with no control function (switch actuator).


Voith Digital Solutions GmbH
Actuators and Governors
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
Effective forces up to 500 kN [112,000 lbf]
Mean time between failures (MTBF) 35 years (estimated, theoretical value)
Supply voltage for the SelCon electronics 24 VDC
Current consumption for the SelCon electronics 5 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 function Internal return spring
Ambient temperature 0 to +60°C (standard version, not rated for use in potentially explosive areas)
Explosion protection (optional)
  • ATEX (II 2G ck IIB T3, Ta = 0 to +60°C)
  • Others upon request
Protection class IP 65
Safety integrity level SIL 2 (upon request)
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
  • Upgrade of systems with the Voith DSG I/H converters, WSR way valves and SMR control servo motors
  • Upgrade of systems with Woodward actuators:
    • Varistroke linear, electro­hydraulic actuator
    • EHPC Electrohydraulic Power Cylinder
    • EHPS Electrohydraulic Power Servo
    • PGPL Hydraulic Powered Electric Actuator
    • EG 3P Hydraulic Amplifier
    • TM 25LP or TM 200LP Linear Proportional Actuators
    • CPC or CPC II Current to Pressure Converters

Advantages and Benefits

Features Advantages Benefits
  • Self-contained, closed hydraulic system.
  • The linear actuator works without an external oil supply.
  • 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 a higher operational reliability. External hydraulic dis­turb­ances such as pressure fluctuations, mismatched line diameters or negative pressure in the tank line are precluded.
  • The considerably reduced fire hazard increases your safety. This may reduce your insurance costs.
  • The linear actuator is an optimal solution for new systems and for retrofits.
  • It is impossible for dirt or water to enter the hydraulic system.
  • You save up to 5 days during commissioning because it is not necessary to flush and vent any pipes.
  • Operation of the SelCon is wear-resistant and main­tenance costs are low.
  • Safety function is provided by a durable return spring and a reliable seat type trip valve.
  • 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 (tripping) and the operating function (control mode) are decoupled.
  • Tripping is initiated by means of a separate safety control circuit.
  • Position control of the hydraulic cylinder using a servo pump (displacement principle).
  • No classic control valves (throttle principle).
  • The linear actuator has a high level of energy efficiency.
  • The level of heat intro­duced into the integrated hydraulic system is low.
  • You reduce energy costs for operating the actuator by up to 50% 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 price and function in your application.
  • The SelCon is a high-quality, cost-effective actuator solution for new systems, retrofits or modernization projects.
  • Low-maintenance design using reliable system components.
  • Very small amounts of operating fluid in the system.
  • The time and money spent on maintenance are minimal.
  • Your costs for maintenance and oil management are considerably less compared to conventional solutions.
  • With significantly reduced oil capacities, you play your part in protecting the environment.
  • Continuous control using an internal gear pump that operates constantly (no intermittent duty).
  • The control system of the linear actuator operates with no response delay.
  • The actuator is ready to operate immediately, especially even 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 Synchronous motor
    2 Voith internal gear pump
    3 Cylinder with internal return spring
    4 Diaphragm accumulator
    5 Trip solenoid valve
    6 Displacement transducer
    7 Piston rod


    The control system activates the SelCon using a 4 – 20 mA standard signal. The stroke of the piston rod is proportional to this standard signal w (setpoint). In the event of a fast-acting trip, the trip solenoid valve opens and connects the two cylinder chambers. The return spring moves the piston rod to its safety position within 300 ms. During this action, the hydraulic fluid flows from one cylinder chamber into the other.

    The SelCon has two functions, namely providing a control function and a safety function (trip). In control mode, the SelCon regulates the position of the piston rod using the setpoint signal 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, the trip solenoid valve opens. The piston rod is moved to its safety position by the energy stored in the return spring. This is carried out in an uncontrolled manner and at high speed.

    An auxiliary electrical power supply is required for operating the SelCon. All electrical components are protected against environmental influences. The electronic position detection system is integrated in the actuator. The control loop parameters for position control and the parameters for scaling the piston rod position are set using the application software implemented in the control unit.