Manual 35132
VariStroke-DX Duplex Hydraulic Servo Skid
Woodward
37
During normal operation the master/slave” indication shows only which unit is designated to be in control
based on connection status of the Discrete input 1.
To confirm which unit is actually in control of the VS-DX skid output pressure the unit in control status
should be verified by the status of discrete output 2, the status indication in the service tool, and the
pressure indicated on the gages.
If a VS-GI fail or need to be disabled, it can be locked out of the system using the control isolation valve.
To ensure there is no electrical transient created on the unit in control, it is mandatory to power down the
failed servo, isolate all its electrical connections inside VS-DX electrical terminal box using dedicated
knife disconnect type terminals.
For a complete procedure of the individual VS-I replacement, see Woodward manual 35133.
When replacing a failed VS-GI Servo, always use the following
order to ensure there are no interactions with the operating servo.
1. Power down the failed unit.
2. Close and lock-out the control isolation valve
3. Close and lock-out the supply isolation valve if necessary (not
provided with VS-DX unit)
4. Close and lock-out the drain isolation valve if necessary (not
provided with VS-DX unit)
5. Ensure the work area around the skid is free from combustible
medium before removing covers.
6. Disconnect all knife disconnect type terminals connected with
unit to be serviced in VS-DX skid electrical terminal box
The VS-DX skid includes provisions for paddle locks to securely lock
out the control isolation valves. Follow all plant designated lock-out
/tag out procedures.
It is recommended that the control is switched periodically between
VS-GI’s to help flush sediment contamination from the VS-DX skid.
Additionally it is recommended that the discrete output that signals
internal faults is connected to the turbine control system. This will
ensure that both servos are functioning at the time of Master/Slave
switchover.
Released
