Field Testing of a Load Reducing Bushing Assembly for Valve Position Indicators

The Arnold Engineering Development Center (AEDC) testing complex includes more than 50 wind tunnels, test cells, arc heaters, and other specialized test facilities. Of these, 27 units have capabilities that are unmatched in the United States, and 14 are unmatched in the world. These unique facilities create equally unique operating environments for instrumentation used for monitoring and control of test conditions. Several high flow-rate, supersonic wind tunnels utilize off-the-shelf angular displacement transducers (ADTs) for monitoring the position of 90° valves (i.e. butterfly valves) used to control the air flow-rate, operating pressure, and temperature during testing. There are significant structural vibrations in the wind tunnels to which the ADTs are subject. These ADTs have experienced an unacceptably high rate of failure during testing. These failures increase maintenance costs, and in some cases can require test operations be suspended while the faulty ADT is replaced; leading to significant cost and schedule impacts associated with the down-time. This paper will discuss an effort to design a bushing assembly to reduce the loads experienced by the ADTs. The bushing assembly redirects vibrational energy from the valves into supporting structure, rather than into the ADT where it could cause bearing wear and ultimately failure. The paper will focus on the efforts to develop a meaningful field test arrangement for the bushing assemblies on one of the wind tunnels at AEDC, and an instrumentation package that monitored and recorded data relative to the performance of the bushing assembly during normal wind tunnel operations. Key results of this test program will be highlighted.