Woodward The VariStroke Actuator offers the following benefits

The VariStroke Actuator offers the following benefits to the user in comparison to

other electro-hydraulic actuators:

Dirt Tolerance—The VariStroke-I actuator is specifically designed for steam

turbine applications where turbine lube oil is also used to power the hydraulic

turbine control valve actuator(s). Steam turbine applications can be extremely

challenging for hydraulic control valve actuators as dirt, metal shavings, water,

and other contaminants (babbitt, ammonia, etc.) are common in such oil

systems. Also due to the high temperatures at which steam turbines operate,

turbine oil breakdown is common, resulting in the creation of a sludge-type

substance and the varnishing of internal system components. However, the

VariStroke-I actuator is designed to operate reliably within such challenging

applications. Its corrosion-resistant materials, single moving rotary valve, 222 N

(50 lbf) of chip shear force, and self-cleaning port design allow it to operate in

such applications without experiencing undesirable sticking or dragging.

Valve Rack Linearization—Since flow-through single and staged inlet steam

valves tend to be non-linear throughout their flow range, turbine controls must be

de-tuned to compensate for instability or sluggish control points throughout this

range. As a way of allowing turbine control optimization, the VariStroke-I includes

an 11-point linearization table to allow turbine OEMs or users to compensate for

poor valve linearization by digitally linearizing the control-to-valve flow

relationship.

Side Load Capability—A common problem with turbine actuators is oil leaking

from their output shaft due to connection to valve rack linkages which have an

arc-type of motion. This motion results in side loading of the actuator shaft, and

after long periods may result in shaft-seal wear and resultant oil leakage.

Designed for a continuous side load of up to 10% of actuator output, the

VariStroke-I actuator incorporates a high-force precision bearing and triple-seal

technology on its output shaft to solve this typical application problem.