Steam Turbine Control

Electric Servo Actuator with Fail-Safe Protection

Steam turbine control system applications have demanding requirements for governor valve actuators. High safety, durability, and positioning accuracy are the key features of steam turbine governing systems. In the event of a trip command from the control system and loss of power, the actuator must close the governor valve within 300-500 ms to avoid turbine rotor over speeding.

Diakont is a trusted supplier of industry-leading electric servo actuators and control systems for the energy industry. Diakont has extensive experience in supplying actuators and control modules for steam, gas and hydro turbine control valves for turbine manufacturers and automation companies worldwide. Diakont’s actuators deliver a direct replacement for hydraulic systems and provide a compact, more cost-effective, and safer solution.

Replacing electrohydraulic and hydraulic actuators in steam turbine control systems with Diakont electromechanical actuators delivers safety, maintenance and durability advantages:

  • Improved safety and reliability with a fail-safe spring mechanism, redundant motor, and encoder
  • No oil issues: fully electric servo actuator design has no leakages from pumps or hoses
  • Low maintenance with a long service life
  • High durability in severe environment conditions
  • Smart digital control unit provides interface for simple integration and troubleshooting
High Safety Options

The fail-safe spring mechanism extracts or retracts the actuator output rod to a safe position at an extremely high speed in the event of trip command or power cutoff. The shock absorbers are mounted in the fail-safe mechanism flange to minimize the influence of shock load on the cone seating surface of the valve.

Diakont electric servo actuators deliver additional reliability with redundant motors containing two independent stators and encoders with connections to independent junction boxes mounted on the actuators.

Oil Free Turbine Control System

Turbine control systems based on electric servo actuators do not require any oil, hoses or pumps associated with hydraulic systems. This greatly reduces maintenance and operation costs. Additionally, this reduces fire hazards (especially for valves mounted on top of turbines), consequently reducing insurance prices.

Low Maintenance with a Long Service Life

Diakont electric servo actuators provide exceptional service life while requiring minimal maintenance. Diakont actuators use advanced roller screw technology which ensures an operation lifetime of 20 years or more. Also, Diakont suggests only re-lubrication maintenance on these actuators once every four years.

Compact Design

Diakont electric servo actuators incorporate progressive technology, including precisely machined roller screws and high-force permanent magnet synchronous motors (PMSM). These components are integrated into a single unit, providing exceptional performance in a compact footprint.

Smart Control Unit

Diakont’s control unit provides the ability to control actuators with an analog or CAN interface and facilitates easy actuator integration, potential fault detection, and troubleshooting service.

Configuration Options:
  • Fail-safe spring
  • Electromechanical brake
  • Terminal box at actuator for easy cable disconnect
  • Redundant motor, encoder and control unit
  • Manual drive and more


Pilot valve control actuator

Steam control valve

direct mounting actuator

Rated force

675 lbf (3 kN)

4 500 lbf 20 kN

14 500 lbf 65 kN


2 in (75 mm)

Up to 5.9 in (Up to 150 mm)

Up to 10 in (Up to 250 mm)

Motion time for full stroke

300 msec

600 msec

600 msec

Failsafe closing time for full stroke


300 msec 300 msec

Positioning accuracy

0.0004” (0.01 mm)


every 4 years


20 years

Safety integrity level

Optional: SIL 2

Protection degree IP65 (optional: IP66)
Hazardous location standard Optional: ATEX Zone 2 
Ambient temperature -40°F  to 185°F (-40°C to 85°C)
Mounting options Trunnion, rear clevis, front flange, custom mounting

Custom Modifications

The specifications listed for the electromechanical actuators are based on typical configurations. However, custom modifications can be made easily to accommodate specific customer requirements. Contact a Diakont representative for more information.

Local Customer Service

Contact a local technical support and troubleshooting representative from Diakont facilities in the USA (San Diego), Italy (Arezzo), and Russia (St Petersburg). Diakont’s field teams support installation, tuning and maintenance. Diakont also has various test benches for endurance and functional testing.