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Post by Johansson on Aug 22, 2017 14:28:54 GMT -5
That sounds like a pretty complex system, I vote for keeping it simple and not add any more valves and stuff than absolutely needed. The syringes shouldn´t get blocked if everything is working properly.
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Post by racket on Aug 22, 2017 16:21:01 GMT -5
Hi Chuksy
It can be as simple as a large ball, steel or glass, that sits down on a seat, the air/gas pressure simply lifts it off to allow air/gas/oil to bypass the scav. pump , when the engine stops , the ball drops down on its seat and prevents air being sucked back from the oiltank .
there are lightweight check valves used in household plumbing
Cheers John
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Post by Johansson on Aug 22, 2017 23:01:30 GMT -5
Here are some pics of the check valve I made for my JU-01 return, I use it in parallel with a single scavenge pump and so far it seems to work perfectly. Cheers! /Anders
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CH3NO2
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Post by CH3NO2 on Aug 23, 2017 11:28:21 GMT -5
John and Anders,
What is the purpose of the scavenge pump if it is being bypassed by the check valve during operation? If the pump only becomes effective after shut down, why is it needed?
Thanks, Tony
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Post by Johansson on Aug 23, 2017 14:21:11 GMT -5
John and Anders, What is the purpose of the scavenge pump if it is being bypassed by the check valve during operation? If the pump only becomes effective after shut down, why is it needed? Thanks, Tony Hi Tony, The scavenge pump is needed during low boost running and pre/post running. During one of my test rig runs with JU-01 I measured the pressure in the scavenge line and it was linear with the P2 pressure but aprox. 1 bar lower, so when the engine passed 1 bar P2 the pressure in the bearing tunnel was above atmospheric. This is when the one way bypass starts to work, it will let the air pressure in the bearing tunnel push oil out of the engine past the already maxed out scavenge pump and into the oil tank. Without it the scavenge pump would restrict the scavenge oil which causes the pressure buildup. Cheers! /Anders
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CH3NO2
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Post by CH3NO2 on Aug 23, 2017 18:27:19 GMT -5
Hi Anders,
I understand the need for the bypass when air is flowing into the outlet side of the oil line. The scavenge pump can't handle the volume of flow.
The part I'm not clear on is why is the scavenge pump is needed at all. It seems the flow resistance through a short oil line back to the tank will be so low that its not much of an issue.
Is the concern a pressure differential between the bearings and atmosphere? A leak path through the bearings and back into the engine?
Thank you Sir! Tony
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Post by racket on Aug 23, 2017 19:25:43 GMT -5
Hi Tony
With a turbo, the oil comes out of the bearings and flows into a large cavity with a 1 inch hole at the bottom , then through an equally large bore pipe running downhill all the way to the airspace in the oil tank .
The problems arise when we make a "micro" type engine with very restrictive flow passageways for the used oil , theres simply not sufficient space to fit 1 inch bore plumbing within the engine and provide a continuous downhill flow path , the oil very quickly backs up , and its only the air/gas pressures on the other side of the seals that prevent oil being forced back into the comp or turb space as happens post shutdown or prestart when those pressures don't exist .
Even with full sized aircraft turbine engines the scavenge pumps need to be considerably larger in capacity to the supply pump , its not uncommon for them to be 4 times greater to cope with the air/oil mix .
A scavenge pump isn't needed for a turbo based engine unless its not possible to have that consistent downhill flow path back to the air space in the oil tank , it must not empty into the oil space in the tank, the oil will backup to the turbo and oil will be forced out of the seals.
I've never used a scavenge pump on any of my engines , the turbo based ones always had that large bore downhill slope back to tank ,so no problems , the "micro" ones have all suffered from smoky shutdowns, often with flames in the turb space from oil igniting after being forced past the seal whilst the oil pump is supply lube to cool the bearings and prevent coking from heat soakback from that big lump of Inconel at the back.
With your engine , as long as its setup in "conventional" turbo fashion , you won't need a scavenge pump :-)
Cheers John
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CH3NO2
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Post by CH3NO2 on Aug 23, 2017 21:39:05 GMT -5
Thanks for the explanations Anders and John. BTW, Is this a supply pump you have mounted on top of a oil tank? Where the turbo oil outlet dumps down to a tank?
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Post by racket on Aug 24, 2017 0:37:28 GMT -5
Hi Tony Yep , thats the supply pump , its mounted on a "cross beam" between the two axle bearing mounts , I think its ~6" X 2" thin metal section with 2mm stainless upright down to the axle mounts , it has to take the weight of the turbo which is mounted to a 2mm stainless plate which is pop riveted to the cross beam . The oiltank is yet to be installed in that pic, the tank fits just below the turbo , can't seem to find a pic of it though :-( Maybe this "walkaround" vid might help www.youtube.com/watch?v=3M8uRIX_yYU Cheers John
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Chuks
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Posts: 498
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Post by Chuks on Aug 25, 2017 12:59:45 GMT -5
tanks Anders,
now I understand how this works,
its something i need to see before I see if I can make mine.
it would be nice if a pressure sensor can be added to automatically switch the oil scavenge pump on and off.
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Post by Johansson on Aug 25, 2017 16:03:51 GMT -5
tanks Anders, now I understand how this works, its something i need to see before I see if I can make mine. it would be nice if a pressure sensor can be added to automatically switch the oil scavenge pump on and off. Nahh, just let the pump run all the time. A pressure sensor is just another piece of electronics that will eventually break down and cause problems.
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Chuks
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Posts: 498
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Post by Chuks on Aug 26, 2017 20:50:20 GMT -5
Hi Chuksy It can be as simple as a large ball, steel or glass, that sits down on a seat, the air/gas pressure simply lifts it off to allow air/gas/oil to bypass the scav. pump , when the engine stops , the ball drops down on its seat and prevents air being sucked back from the oiltank . there are lightweight check valves used in household plumbing Cheers John Hi John, Now I get what you meant by that.... I compared my first video vs my last video, I noticed that in the last video the scavenge pump rubber plumbing didn't last more than 1 minute while in the previous ones without the scavenge pump lasted for at least 10 minuts. am thinking its pressure plus temperature in action because of the restrictive scavenge pump. also when the oil starts to leak through the rubber plumbing, it keeps spraying as if there is an even higher pressure pump inside the engine. I got a very beautiful check valve that I will use for the engine
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Chuks
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Posts: 498
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Post by Chuks on Aug 26, 2017 21:00:24 GMT -5
because I lost my phone I can't post a picture of it, I will post the cad model instead. check valve by Chuks Anthony, on Flickr cheers Chuks
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Chuks
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Posts: 498
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Post by Chuks on Aug 26, 2017 21:04:09 GMT -5
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Post by racket on Aug 26, 2017 22:28:43 GMT -5
Hi Chuksy
A nice little "flapper" valve , that'll do the job , mounted "vertically" so the natural tendency is for the valve to close , any gas pressure will easily lift it .
Neat solution to your filter :-)
Cheers John
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