RE 08120, Edition: 2013-02, Bosch Rexroth AG

Electro-mechanical Actuator with Hydrostatic Drive For Actuation and Control Functions in Valve Armatures

Contents

Introduction 2System Structure 2Features 2Advantages 2Applications 2Schematic Diagram and Function 3Application Example 3Approved System Components 4

RE 08120Edition: 2013-02Technical Information

2/4 Technical Information | Electro-mechanical Actuator with Hydrostatic Drive

Bosch Rexroth AG, RE 08120, Edition: 2013-02

Everything under Control – with the electro-mechanical Actuator for Control Functions

IntroductionThe electro-mechanical actuator with a hydrostatic drive system is designed to complete the range of the existing hydraulic actuators for the control, stop and trip func-tions in valves.The actuator is suitable for mounting on valves, which are used for the control of liquids, gases and steam with SIL3 safety level.

System StructureThe electro-mechanical actuator consists of a hydrostatic linear drive and a superimposed spring-supported trip function.

Features ▶ Electrical interface for power and signal transmission ▶ Positioning by closed-loop controlled synchronous

motor and hydrostatic drive ▶ Superimposed trip function by spring supported

closing function ▶ Limiting the maximum trip speed ▶ Integrated damping function ▶ SIL3-capable version

Advantages ▶ No external power unit ▶ No installation of hydraulic pipes ▶ Clear and concise control ▶ Easy parameterization with provided software ▶ Low maintenance efforts ▶ Use of proven components ▶ Robust construction ▶ Short length ▶ Suitable for large forces and strokes ▶ Insensitive to vibration ▶ Simple sealing concept ▶ Energy-efficient solution ▶ Reduced fire hazard

Applications ▶ Valve-actuating devices in gas and steam turbines ▶ Butterfly valves with fail-safe position ▶ Retrofit projects ▶ Stand-alone applications ▶ Valves with fast opening function

Application ExampleThe steam supply to a turbine must be controlled and stopped in case of accident. This function takes an electro-mechanical actuator with a hydrostatic drive, which is mounted on the valve.

Electro-mechanical Actuator with Hydrostatic Drive | Technical Information 3/4

RE 08120, Edition: 2013-02, Bosch Rexroth AG

Control

Hydrostatic drive with trip function

Divided closing piston

Control piston

Position

Pressure

Switch and status signals

Electrical power

Signal transfer

with master control

Schematic Diagram and Function

The trip end position of the actuator is also defined as the zero position of the actuator. In this situation, the right closing piston is positioned with the spring force in the right end position, which also means that the valve is closed.

The tensioning of the spring is effected by pressurizing the control piston, which moves to the right and increases the preload of the built-in valve-closing spring.

By pressurizing the ring chamber of the divided closing piston, a hydraulic coupling is achieved with the control piston.

In the closed-loop control position the divided closing piston is moved by position control in combination with the control piston and the tensioned spring to dose the media supply (liquid, gas, steam) in a plant.

The trip function (see above) is achieved through the interruption of the switch signals, so that primary, the pressure is released in the piston ring chamber of the right closing piston, and thus, the valve closing function is triggered by the spring.

Bosch Rexroth AG HydraulicsZum Eisengießer 197816 Lohr am Main, Germany Phone +49 (0) 93 52 / 18-0 documentation@boschrexroth.de www.boschrexroth.de

© This document, as well as the data, specifications and other information set forth in it, are the exclusive property of Bosch Rexroth AG. It may not be reproduced or given to third parties without its consent.The data specified above only serve to describe the product. No statements concerning a certain condition or suitability for a certain application can be derived from our information. The information given does not release the user from the obligation of own judgment and verification. It must be remembered that our products are subject to a natural process of wear and aging.

Bosch Rexroth AG, RE 08120, Edition: 2013-02

4/4 Technical Information | Electro-mechanical Actuator with Hydrostatic Drive

Approved System Components

The actuator contains a control and a divided closing pis-ton. The power generated by the hydraulic pump is sup-plied to the position control loop depending on the demands of the sequence program.

The hydraulic pump – driven by the synchronous servo motor – acts as a hydro-mechanical energy converter, i.e. the mechanical power released by the servo motor is converted into an equivalent hydraulic performance.

The synchronous servo motor represents the electro-mechanical part of the hydrostatic drive. It is characterized by high dynamics at specified rotation speed set value changes, and is part of the actuator position control loop.

The drive control unit consists of a control and a power unit. It includes all the logical con-nections, which are necessary for the proper operation of the actuator in its various modes of operation, and supplies the electric power demand for driving the servo motor.