Rotor thrust balance pressure.

Mk-1533 through 1535 discussions.

Rotor thrust balance pressure.

Postby j79guy on Sun Feb 15, 2009 7:27 pm

Ok, general question; What should the pressure be, acting on the backside of the compressor rotor on Mk-1533, Mk-1534 and Mk-1535 Avon units, @ ISO conditions, @ Full rated power?
On the GE engines, (LM1500) this is closely monitored, and adjusted to give optimum loading of the Centre Bearing assembly. The basic construction of the Industrial Avon is virtually identical to the GE LM1500, therefore the mechanics will be the same, as far as bearing loading. Rolls is having reliability issues with the Centre Bearings, and their "fix" is the change the bearing material specifications. (Treat the symptom, not the problem, which is rooted in improper bearing loading.) I see that with the Mk-1534 and Mk-1535 compressor rotors, Rolls put a smaller diameter rear air seal arrangement on, to change the Centre Bearing loading, but I want to know more. What "should" this pressure be, to give optimum loading. Then we can alter the compresor rear air seal clearances, and/or vent orificing to reach a pressure that gives the best bearing life.
I quite expect this information to not be available to the general public, but there's no harm in asking.
Short of a figure, one could set an engine on the test cell with tight rear air seal clearances, and use successively smaller vent orifices at contant engine load, to determing what gives the lowest Centre bearing oil drain temp, and then go up in pressure a bit to ensure positive axial loading. A lengthy process, but ultimately a worthy goal to gain this valuble information.

On the Industrial Spey engines, this pressure is called "S-266" by Rolls. Maybe there is some reference to rotor thrust balance pressure somewhere on the Avons?

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