Woodward 9902-406 Variable Stator Vane Control

Changes in turbine speed alter the flyweight force and pilot-valve position, which changes the hydraulic servo response.

The CIT sensor introduces a temperature-dependent bias into the control relationship between turbine speed and output-shaft position.

The manual describes approximately 24 L/min (6.4 US gal/min) of oil supplied to the customer-supplied filter and approximately 7.6 L/min (2 US gal/min) of cooling oil bypassed through the bypass-valve orifice during operation.

When vane movement does not follow the expected hydraulic or mechanical response, the VSV control becomes a logical inspection point together with linkage, hydraulic supply and actuator components.

Abnormal response associated with turbine speed or compressor inlet temperature can lead maintenance teams to check the VSV control chain and its mechanical feedback arrangement.

Because variable stator vane positioning contributes to compressor operating behavior, an unresolved control problem can restrict normal turbine operation and increase the risk of extended troubleshooting or forced downtime. Replacement should therefore be matched to the complete installed configuration.

Covered by the same VSV family manual. The manual provides a dedicated 9902-332 specification column and an outline drawing shared with 9902-406.

VSV Variable Stator Vane Control for non-airborne gas turbine applications. The manual specifically includes 9902-406 and provides a shared outline drawing for 9902-332 / 9902-406.

Another model in the same manual. Its specification column has different inlet/outlet pressure and drive characteristics, so those values should not automatically be substituted for 9902-406.

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Because the VSV control participates in a hydraulic control loop that links turbine speed, compressor inlet temperature, servo action and mechanical feedback. A replacement therefore has to match the installed turbine configuration rather than being selected only because the outer appearance is similar.

The complete part number and serial number are important when requesting service or replacement support. The installed hydraulic arrangement, turbine interface, feedback linkage and operating environment should also be checked against the actual system configuration before installation.

The manual specifically states that the VSV control is calibrated by Woodward to the turbine manufacturer's specifications and cannot be repaired or calibrated in the field. If response is abnormal, the wider hydraulic, linkage and actuator arrangement should be investigated instead of attempting to adjust the control itself.

The VSV control's moving parts and hydraulic supply pressure use oil supplied from the turbine's lubricating-oil tank. The specified filtration is 10 µm, and the manual calls for the turbine manufacturer's oil-check and fluid-replacement requirements to be followed. Poor hydraulic conditions can therefore affect system behavior even when the VSV control itself is not the only possible fault point.

The three models are covered together within the VSV control family, but the published specification table gives different operating values for 9902-332 and 9902-405 and does not provide a separate 9902-406 column. Therefore, values belonging to another model should not be transferred to 9902-406 by assumption. The complete part number, installed turbine configuration and applicable engineering requirements should be matched before replacement.

Send the complete part number, quantity, destination, required date and machine/system details for quotation checking.