New VariStroke High Force Tolerance Actuators
Uptime and reliability are essential to the operation of steam and hydro turbines and Woodward’s new VariStroke family of actuators superbly addresses these concerns. Their patented dirt tolerant and self cleaning technology ensures greater overall reliability. The VariStroke linear electro-hydraulic actuators are designed specifically for steam and hydro turbine applications. Two sizes accommodate the required bore and stroke and work on mechanical or generator-drive applications. These linear actuators utilize low-pressure, hydraulic oil (typically from the turbine’s lube oil system) to provide the output shaft force needed to position the inlet valves on steam and hydro turbines. Their superb accuracy and resolution make them ideal for precise speed and load control.
The VariStroke I replaces Woodward’s legacy hydraulic amplifiers while the VariStroke II replaces the Woodward Electrohydraulic Power Cylinder (EHPC). Both actuators are configurable via a simple user-friendly, computer-based service tool, allowing users to easily configure, calibrate, and adjust all internal functions and response settings. The VariStroke’s integrated driver includes a 4-20 mA output to indicate control valve output shaft position, along with unit alarm and shutdown relay outputs for unit health and status indicators. The 4-20 mA demand inputs and dual redundant shaft position sensors allow the actuator to continue operating even with demand input or feedback sensor failures, ensuring extended runtimes between forced outages and online system repair.
The overall installed cost for this fully-integrated actuator is low because it is completely assembled and tested at the factory, greatly reducing system fabrication, testing, and site assembly time. In retrofit applications, the VariStroke actuator can be used to directly replace the existing servo system, which saves costly repairs to existing, aging servos, eliminates the difficulty of obtaining spare parts for obsolete equipment, and reduces calibration time.
This product announcement originally appeared in Woodward’s Industrial Controls News, April 2016.
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