A320 Engine No4 Bearings

[EMER_CANC]

Just wondering why is the Engine No4 bearing monitored as opposed to any of the other bearings? In addition, what is the purpose of the scavenge valve? Does the Scavenge Valve being stuck in closed/open position inflight present any serious threat to engine operations?

Thanks
EC

[allthatglitters]

I can assume we are talking about the IAE V2500 powered A320. Currently running thru my course notes. Seem to remember the No.4 bearing compartment situated in a high temperature, high pressure enviroment at the centre of the combustion section.
The No 4 bearing Scavange Valve has 2 postions Open and Min, (not fully closed).

[EMER_CANC]

Apologies... I was refering to the V2500s.

Why is it monitored? And what purpose does the Scavenge Valve play?

Cheers
EC

If the Scavenge Valve only moved into Min position, when then would a No4 Bearing Hi Press ECAM be triggered. This ECAM if I am correct, occurs when the valve is stuck in the closed position.

Cheers
EC

[Blacksheep]

There is a reliability issue with the No. 4 bearing on the V2500 engine. Monitoring bearing performance is part of the solution and the effects of scavenge valve operation are important to the final 'fix' for the No. 4 bearing problem.

We don't engage in knee jerk fixes when it comes to reliability engineering. Unless safety is involved, discreet monitoring is generally the best way forward.

[DoctorA300]

Some knee jerk reaction time you have in borneo Blackie, I did the A320 course 10 years ago, it had the 4th bearing scav valve even then.
The function of the valve is to restrict the scavenge line from the 4th bearing at high N2. The reason for this is, at high N2 and thereby high oil press, the oil "flushes" through the bearing compartment and does not remove enough heat. The restriction slows down the oil and it removes more heat.
Hopes this helps.
Cheers
Doc

[granard]

The reason for the valve is got to do with pressure diff across the carbon seal in the compartment.

Out side the seal you have 12 stage air ,which cools the compartment,this stage air on one side of the bearing has to be blanced by back pressure caused by the ristriction made by the valve.

[Blacksheep]

Got me knickers in a knot there Doc. It was a No. 3 that blew up on us - which seems to have got IAE very excited too, incidentally... :O

[Golden Rivet]

DocA300 is no more. May he rest in piece.