TFE731 Winter 2004 - Special Edition

Oil Pressure Spikes During Cold Weather Operation With 3060785-1/2 Oil Pump

— John Pursell (Honeywell)

Duncan Aviation editor's note: The following information, provided directly from Honeywell, provides excellent, timely information for our TFE731 operators.

With the introduction of the 3060785-1/2 oil pump, reports of high oil pressure spikes during engine start and occasionally initial high power settings have been reported. Such occurrences are typically associated with low outside air temperatures which influence the engine oil temperatures. In some instances, the reported oil pressure spikes exceeded the applicable flight manual recommendations.

The 3060785 pump was introduced primarily to improve transfer gearbox scavenge thus improving the carbon seal buffering pressure during engine start. Also during the redesign, the lube discharge passages were enlarged to improve cavitation erosion resistance and overall lube capacity. As a result of this passage enlargement, there is an internal pressure drop within the pump. With this internal pressure drop, the transient pressure rise of the regulated pressure is faster.

The oil pressure regulator contains an orifice which is intended to dampen the response of the pressure regulator in hot oil conditions. The orifice was added to eliminate pressure oscillations initially experienced with the 3060785 pump.

This same orifice with cold oil temperatures (high viscosity) is slow to respond to the 3060785 oil pump increased capacity can result in pressure spikes during low outside air temperatures and cold oil situations.

The cold oil pressure spikes observed have been as high as 110 PSI with ambient temperatures near 0 degrees F. The oil pressure regulator features a cold start relief valve that bypasses oil at 200 PSI. This valve is sized to be well within the proof pressure of the lube system. Therefore, the start pressure does not represent a condition which could harm the engine or related oil systems.

Furthermore, the oil pressure transducer which communicates with the cockpit indication system is routinely designed for 4X of full-scale proof pressures (above which the transducer requires calibration.)

Honeywell Engine manuals will be revised to note that higher than maximum oil pressures may be observed during start and initial engine operation with cold oil conditions, when equipped with the 3060785-1/2 oil pump.

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