Inlet Valve Failure Root Cause Analysis

Inlet Valve Failure Root Cause Analysis

Wayne Jones

WEC specialist engineers were requested to assist a major airframe manufacturer suffering a series of sudden, unexplained, in service equipment failures.


The project

Following ten years of successful in-service operation airlines were experiencing a number of failures of fuel tank inlet valves. Tank inlet valves were failing to open when commanded during pre-flight tank refuel, leading to flight delays and cancellations.

  • Working alongside the client and equipment supplier engineers from WEC conducted an examination of returned, failed valves and observed that a seal in the valve seat had been extruded from the housing thus jamming the valve.
  • Further Investigations by WEC into the operation of the fuel system concluded that the most probable cause of the seal extrusion was thermal expansion of cold fuel trapped within the valve following in-flight fuel transfers, descent and subsequent ground operation. The consequent increase in pressure extruding the seal and, in some cases, causing damage to the valve.
  • Following collation of in-service data and checking serial numbers against manufacturing dates, WEC engineers further concluded that the problem was more prevalent in tropical regions (descent into very warm conditions) and more common amongst later valve production batches.
  • Working alongside the client’s equipment supplier WEC engineers concluded that whilst the valve was manufactured correctly to extant drawings, new production facility equipment meant that achieved manufacturing tolerances, whilst still compliant to specification, were closer than previously attained thus leading to the change in equipment behaviour.

WEC then worked alongside the client and equipment manufacturer to develop and supply a modified valve to the affected fleet.

Two men discussing designs on computer
Pipe close up

The benefit

By identifying the root cause of the equipment failure, WEC engineers were able to support the client and their equipment supplier with replacing the failed valve type. The replacement valve was similar to the original design, but with provision for pressure relief.

By eliminating the recurrent equipment failures, the project reduced the number of associated aircraft flight delays and cancellations with considerable cost savings for both the operator and client.

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