My first post here, I have seen some interesting threads while lurking, and I thought I could chime in for a little tip here.
I thought I should pass this little note along reminding engineers to do such a simple task during your routine overhauls of your older ABB/BBc VTR series turbochargers.
This past week I did a rotor exchange on an ABB VTR 454 P11 turbocharger (T/C) on a Wartsila 8L38 engine. The T/C had been serviced about a year prior, however in recent months the turbine side (T/S) oil would turn black in a matter of hours. Additionally at full load, sparks from combustion gas could actually be seen emanating from the T/S bearing chamber vent on the gas inlet (G/I) casing. The sight glasses had turned completely black and the crew was literally in the dark as to what was going on. The vessel shall remain anonymous to protect the innocent.
What I found below was behind the bearing cover. It looks black, and maybe you won't think this is such a big deal, but carbon and oil make a great grinding compound for roller bearings! However, behind that pump is a centrifuge. That centrifuge has three oil jets that are about 0.5-0.75mm on diameter. Two were blocked entirely, the last one was very close to being blocked. With no oil, at 14 000 RPM and a rotor weight of around 100 kg's - well it wouldn't take long for the heat to build and a serious catastrophic bearing failure was imminent. Likely in seconds completely destroying the entire rotor, cover ring and wall insert and possibly if the load on the engines was high enough at the time, total loss of the turbocharger at great expense and downtime.
All of this because the previous service engineer didn't simply check to see if the clearing air passage was ...clear!
Let me explain the clearing air passage and it’s duty to turbocharger life. On all of the roller bearing style ABB T/C's(VTR 0,1 and 4 series) there is a passage that starts just outside the partition wall at the diffuser area, bleeding a small amount of pressurized air though a passage in the gas outlet (G/O) casing, and around a channel into the G/I casing, and then thought to the shaft area between the bearing chamber and the turbine blades. This air pressure will be higher than the exhaust gas pressure, and will tend to keep the exhaust gas pressure from traveling down the shaft into the bearing chamber where it can do as shown below. A simple air seal (downstream of the more complicated labyrinth seals).
So next time you happen to be doing a turbocharger rotor swap, and the rotor is out, take the 10 minutes to get an air line down to the turbocharger, wrap a rag around the end of the hose and give the passage a good blow from the compressor side. You should be able to feel some air flow as you put your hand up in to the seal bush area. A failure to follow this simple step just about cost this vessel a turbocharger.
Just a little heads up to keep it all running smooth on your aging ABB/BBC VTR series turbochargers.