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Post by turboron on Dec 28, 2020 7:50:44 GMT -5
Progress
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Post by madpatty on Dec 29, 2020 8:37:26 GMT -5
Hi Guys.
What do you think is the lubricant feed(fuel oil mix in my case) pressure requirements for the squeeze film dampers?
Thanks
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Post by turboron on Dec 29, 2020 13:34:52 GMT -5
Patty, my understanding is that you just need enough pressure to maintain flow though the cavity (annulus). I assume 5 psig should be sufficient.
Thanks, Ron
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Post by racket on Dec 29, 2020 16:14:53 GMT -5
Hi Patty
If its bled off your fuel supply to the engine then there'll be "compensation" for your P2 pressure , even though your shaft tunnel will be at a lower pressure , so "extra" pressure provided at higher power setting
Cheers John
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Post by turboron on Dec 29, 2020 16:19:36 GMT -5
Patty, the 5 psig is a delta pressure over the sump or discharge pressure the damper sees.
Thanks, Ron
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Post by madpatty on Dec 29, 2020 22:51:25 GMT -5
On a side note- Here's the previous damper journal. The point shows where the journal has contacted the housing. O-rings weren't enough to provide required damping. Regards.
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Post by racket on Dec 30, 2020 20:04:03 GMT -5
Hi Patty Finally found the, LOL... "official" drawing of the 9/94 engines shaft tunnel It might help explain what I did Cheers John
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Post by madpatty on Dec 31, 2020 0:16:54 GMT -5
Hi Patty Finally found the, LOL... "official" drawing of the 9/94 engines shaft tunnel It might help explain what I did Cheers John Hi Racket. Thanks for sharing the “official” pic. I was able to make a turbo style damper. The “lands” on either side of the centre oil groove are just 10 thou diametrically lesser than the housing bore. Now here’s the problem- I don’t have a proper drain from the housing and rely on the oil that will be used up for bearing lubrication (through those small holes visible in the picture). I suspect I may flood the housing area between the bearings with oil. So here’s the test plan- I have decided to go with 15w-40 oil instead of fuel oil mixture to getting best possible damping due to oil’s higher viscosity. I will have a separate oil supply for the damper supply. Maybe run the engine without damper oil supply or very less oil supply till I am close to the critical speeds and then turn on the oil flow more and just try to get over the critical speed hump. I will be essentially controlling 2 knobs, fuel flow to engine and oil flow to damper. The target is to get it over the hump now and prove that damping is working. I will have to make a new housing for extended run then if this setup works. It’s gonna be a tricky run. Regards.
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Post by racket on Dec 31, 2020 0:55:41 GMT -5
Hi Patty
With 0.005" gap there won't be much oil getting into those sharp edged holes , I think I'd be doing a lube test of the system ( minus shaft) to determine just how much lube gets through , you might be surprised just how little unless theres considerable pressure
Cheers John
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Post by madpatty on Dec 31, 2020 1:36:46 GMT -5
Hi Patty With 0.005" gap there won't be much oil getting into those sharp edged holes , I think I'd be doing a lube test of the system ( minus shaft) to determine just how much lube gets through , you might be surprised just how little unless theres considerable pressure Cheers John Hi Racket. There’s another passage for oil. The hole at the centre of the damper is for rotation prevention pin, which is loose fit in the damper to enable some radial and axial motion so that damper feels all the forces. The oil can leak from the sides of that pin as well. It will still leak inside the damper and lubricate the bearings. I did an insitu test with diesel and it leaked more from near that pin than those holes. Regards
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Post by racket on Dec 31, 2020 2:20:58 GMT -5
Hi Patty
OK , so the securing hole isn't a blind hole , we have to be careful not to have too much lube as it causes the balls to skid , I ran into this problem with the steel balls developing "equator wear rings" , you may need higher preload forces to help prevent skidding .
Is the cartridge lube being delivered through the securing pin like a BB turbo ??
Cheers John
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Post by madpatty on Dec 31, 2020 2:52:11 GMT -5
Hi Patty OK , so the securing hole isn't a blind hole , we have to be careful not to have too much lube as it causes the balls to skid , I ran into this problem with the steel balls developing "equator wear rings" , you may need higher preload forces to help prevent skidding . Is the cartridge lube being delivered through the securing pin like a BB turbo ?? Cheers John Hi Racket. The hole isn’t blind so that the bolt shouldn’t tighten against the hole and thus allow damper to essentially float freely and do its job. Read a few patents from Garrett and turbonetics and all of them particularly specify this. The oil is delivered through a separate feed from the bottom of the housing and the securing hole including the oil supply holes are towards the top. This is just a proving setup which will just be used to cross the critical speed. That’s the best arrangement I could make of the existing shaft tunnel. Too much lube is bad that’s why i am thinking of increasing the oil flow as we are close to critical speed and then just cross it successfully and end the test run. All my previous test runs have been been just 20-30 seconds long so I am hoping oil won’t flood up inside the tunnel so rapidly. Regards
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Post by racket on Dec 31, 2020 4:17:36 GMT -5
Hi Patty
My thoughts were that a blind hole wouldn't allow lube entry but still allow "movement" from radial clearance between securing bolt and hole , I wasn't considering bottoming out of the bolt in the hole , just pinning it so that the entire cartridge can "rattle" a tad .
I still feel you need to do the lube flow test with the 15W-40 rather than diesel just to satisfy yourself that the thicker fluid will flow at the pressures you'll be supplying it at .
If the amount of flow is fairly modest , say <100 ml/min , then I'd be inclined to simply hit the lube pump switch immediately before the starter and don't worry about ramping up lube flow , you may need to "prelube" the damper to make sure its filled, then drain the bearing cavity prior to installing the engine on the teststand and firing it up .
Yep , I agree with your thoughts to simply get through the critical speed and run the engine up to decent RPM settings before shutting down.
All the best with the testrun , my thoughts and best wishers go with you :-)
Cheers John
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Post by turboron on Dec 31, 2020 5:35:00 GMT -5
Patty, I support John's latest post. I would test to determine oil flow. I am not sure how important the amount of flow is as long as there is some. Prelube to fill the damper before the run and then turn on the damper flow after the engine starts say at idle. Do not adjust as you run through the critical. The report that you have more than one critical(as evidenced by the compressor bearing failure) in the area is a concern. How are you addressing that issue?
Thanks, Ron
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Post by racket on Dec 31, 2020 5:46:22 GMT -5
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