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Old Dec 09, 2010, 04:21 PM
Emimec
Guest
n/a Posts
Gas Turbine oil seal question

Studying jet engines recently, it crossed my mind how is the oil "sealed" in
the mainshaft. At the high RPM, I cant imagine it being a common oil seal
like used on car engine crankshafts, and a total loss system sounds dubious
to me for a modern engine. Anyone know ?
Bob
Old Dec 09, 2010, 07:43 PM
Rusty Hinge
Guest
n/a Posts
Re: Gas Turbine oil seal question

Emimec wrote:

> Studying jet engines recently, it crossed my mind how is the oil "sealed" in
> the mainshaft. At the high RPM, I cant imagine it being a common oil seal
> like used on car engine crankshafts, and a total loss system sounds dubious
> to me for a modern engine. Anyone know ?


I don't, but it could be centrifugal? If you don't get a definitive
answer in the group, there's an airfield a couple of miles from here,
and there are some pretty high-powered ex RAF types - one is bound to
know, and I owe them a visit.

(Got a lot of pics from last year's air show)

--
Rusty
Old Dec 09, 2010, 08:06 PM
Peter Fairbrother
Guest
n/a Posts
Re: Gas Turbine oil seal question

Emimec wrote:

> Studying jet engines recently, it crossed my mind how is the oil "sealed" in
> the mainshaft.



Not very knowing here, but afaik it isn't? - there is no oil sump to seal?


Now jet engines do have oil, and oil seals, but they are only used to
lubricate the bearings, which is a continuous flow process. There is no
big wet sump, or the like, just a return tank which has no rotating
parts or seals.

or so I imagine, don't really know.

I do know that small turbines as in model turbines and Predator-type
drones and cruise missiles do use total loss, and actually maybe big
ones might too - why not, the fuel is oil anyway?





At the high RPM, I cant imagine it being a common oil seal

> like used on car engine crankshafts, and a total loss system sounds dubious
> to me for a modern engine. Anyone know ?



I know quite a lot about high temp and high pressure differential seals,
but those are used in rocket engines, not jets.

-- Peter fairbrother




> Bob
>
>
Old Dec 09, 2010, 08:36 PM
Peter Fairbrother
Guest
n/a Posts
Re: Gas Turbine oil seal question

Peter Fairbrother wrote:

> Emimec wrote:

>> Studying jet engines recently, it crossed my mind how is the oil
>> "sealed" in the mainshaft.

>
>
> Not very knowing here, but afaik it isn't? - there is no oil sump to seal?
>
>
> Now jet engines do have oil, and oil seals, but they are only used to
> lubricate the bearings, which is a continuous flow process. There is no
> big wet sump, or the like, just a return tank which has no rotating
> parts or seals.
>
> or so I imagine, don't really know.
>
> I do know that small turbines as in model turbines and Predator-type
> drones and cruise missiles do use total loss, and actually maybe big
> ones might too - why not, the fuel is oil anyway? -though they don't in practice


:)


>
>
>
>
>
> At the high RPM, I cant imagine it being a common oil seal

>> like used on car engine crankshafts, and a total loss system sounds
>> dubious to me for a modern engine. Anyone know ?

>
>
> I know quite a lot about high temp and high pressure differential seals,
> but those are used in rocket engines, not jets.
>
> -- Peter fairbrother
>
>
>

>> Bob
>>
Old Dec 10, 2010, 07:20 AM
Richard Shute
Guest
n/a Posts
Re: Gas Turbine oil seal question

On Thu, 9 Dec 2010 22:21:28 -0000, "Emimec"
<emimec.19@NOSPAMbtinternet.com> wrote:


>Studying jet engines recently, it crossed my mind how is the oil "sealed" in
>the mainshaft. At the high RPM, I cant imagine it being a common oil seal
>like used on car engine crankshafts, and a total loss system sounds dubious
>to me for a modern engine. Anyone know ?
>Bob
>

I did some test & research work on an old Rover GT (30 years ago) and
later some studies on helicopter enigines & drives. The main shaft oil
is generally only encouraged not to leave too quickly rather than
'sealed'. Some systems use fine wire brushes, but more advanced
designs have pumping labyrinths eg a coarse 'thread' on the rotating
part what runs with a small clearance within the housing. It works
similar to an Archemedian screw. Some systems use a pressure bleed
from the compressor to 'blow' lubricant through the bearings.

My (very limited) experience was 25 years ago so it may well have been
superseded by more modern advances, especially in high temperature
materials for fully closed seals.

Richard
Old Dec 10, 2010, 08:00 AM
John
Guest
n/a Posts
Re: Gas Turbine oil seal question

Probably a myth, but:

In the very early days of the jet engine Pratt and Whitney made an
engine under licence from RR. Everything went well until they tested
it and had to put a large container underneath to catch the oil which
was being expelled at a high rate. They also had to feed it in very
quickly to make it up. The oil seal on the main shaft had a thread on
it so that it "screwed" the oil back in. The Americans had made the
thread the wrong way round so that it expelled the oil rather than
retaining it.

John
Old Dec 10, 2010, 11:43 AM
Cliff Coggin
Guest
n/a Posts
Re: Gas Turbine oil seal question

"John" <johnmanders@freenetname.co.uk> wrote in message
news:21dfc839-a882-4cfc-b1cd-32c9147f0b4a@p8g2000vbs.googlegroups.com...

> Probably a myth, but:
>
> In the very early days of the jet engine Pratt and Whitney made an
> engine under licence from RR. Everything went well until they tested
> it and had to put a large container underneath to catch the oil which
> was being expelled at a high rate. They also had to feed it in very
> quickly to make it up. The oil seal on the main shaft had a thread on
> it so that it "screwed" the oil back in. The Americans had made the
> thread the wrong way round so that it expelled the oil rather than
> retaining it.
>
> John


Sounds plausible given that NSAS couldn't convert Imperial to metric for the
shuttle, but on the other hand British bikes of that era were notorious for
leaking oil so British engineering skills were equally poor.

Cliff Coggin.
Old Dec 10, 2010, 12:19 PM
David Billington
Guest
n/a Posts
Re: Gas Turbine oil seal question

Cliff Coggin wrote:

> "John" <johnmanders@freenetname.co.uk> wrote in message
> news:21dfc839-a882-4cfc-b1cd-32c9147f0b4a@p8g2000vbs.googlegroups.com...
>

>> Probably a myth, but:
>>
>> In the very early days of the jet engine Pratt and Whitney made an
>> engine under licence from RR. Everything went well until they tested
>> it and had to put a large container underneath to catch the oil which
>> was being expelled at a high rate. They also had to feed it in very
>> quickly to make it up. The oil seal on the main shaft had a thread on
>> it so that it "screwed" the oil back in. The Americans had made the
>> thread the wrong way round so that it expelled the oil rather than
>> retaining it.
>>
>> John
>>

>
> Sounds plausible given that NSAS couldn't convert Imperial to metric for the
> shuttle, but on the other hand British bikes of that era were notorious for
> leaking oil so British engineering skills were equally poor.
>
> Cliff Coggin.
>


I spent a couple of years living in Wichita Kansas and a guy I knew
there had dealt with British bikes in the past, he said the problem
wasn't with the engineering but with the assembly. He said if you took
the bike engine apart and put it back together properly then in his
experience they didn't leak.
Old Dec 10, 2010, 12:58 PM
Emimec
Guest
n/a Posts
Re: Gas Turbine oil seal question

"John" <johnmanders@freenetname.co.uk> wrote in message
news:21dfc839-a882-4cfc-b1cd-32c9147f0b4a@p8g2000vbs.googlegroups.com...

> Probably a myth, but:
>
> In the very early days of the jet engine Pratt and Whitney made an
> engine under licence from RR. Everything went well until they tested
> it and had to put a large container underneath to catch the oil which
> was being expelled at a high rate. They also had to feed it in very
> quickly to make it up. The oil seal on the main shaft had a thread on
> it so that it "screwed" the oil back in. The Americans had made the
> thread the wrong way round so that it expelled the oil rather than
> retaining it.
>
> John


Thanks to everyone's input. I figured the oil must be under pressure for the
"main shaft bearings", as in a car engines main bearings, but couldn't
imagine a car type oil seal holding it all in, especially at the RPM a
turbine runs at. I'll settle for the screw idea, seems the most likely
answer, along with it being forced back into the engine by air/wind.
Bob
Old Dec 10, 2010, 01:47 PM
Rusty Hinge
Guest
n/a Posts
Re: Gas Turbine oil seal question

Cliff Coggin wrote:

> "John" <johnmanders@freenetname.co.uk> wrote in message
> news:21dfc839-a882-4cfc-b1cd-32c9147f0b4a@p8g2000vbs.googlegroups.com...

>> Probably a myth, but:
>>
>> In the very early days of the jet engine Pratt and Whitney made an
>> engine under licence from RR. Everything went well until they tested
>> it and had to put a large container underneath to catch the oil which
>> was being expelled at a high rate. They also had to feed it in very
>> quickly to make it up. The oil seal on the main shaft had a thread on
>> it so that it "screwed" the oil back in. The Americans had made the
>> thread the wrong way round so that it expelled the oil rather than
>> retaining it.
>>
>> John

>
> Sounds plausible given that NSAS couldn't convert Imperial to metric for the
> shuttle, but on the other hand British bikes of that era were notorious for
> leaking oil so British engineering skills were equally poor.


Inded - my (BSA) B31 was known locally as 'The Torrey Canyon'

--
Rusty
Old Dec 10, 2010, 01:54 PM
Rusty Hinge
Guest
n/a Posts
Re: Gas Turbine oil seal question

David Billington wrote:


> I spent a couple of years living in Wichita Kansas and a guy I knew
> there had dealt with British bikes in the past, he said the problem
> wasn't with the engineering but with the assembly. He said if you took
> the bike engine apart and put it back together properly then in his
> experience they didn't leak.


It's generally the primary chaincase - many of them were pressed steel
and split vertically.

The oil 'seal' was a 'V'-shaped rubber ring which went over the two
halves, and a band of alloy channel which compressed the rubber when the
ends were screwed together with a 3/16 BSF bolt at the back.

The only way I ever found to keep that arrangement oiltight was to warm
the chaincase and pour in a goodly quantity of hot paraffin wax.

--
Rusty
Old Dec 10, 2010, 03:49 PM
newshound
Guest
n/a Posts
Re: Gas Turbine oil seal question


>
> Thanks to everyone's input. I figured the oil must be under pressure for
> the "main shaft bearings", as in a car engines main bearings, but couldn't
> imagine a car type oil seal holding it all in, especially at the RPM a
> turbine runs at. I'll settle for the screw idea, seems the most likely
> answer, along with it being forced back into the engine by air/wind.
> Bob

AFAIK they all run on ball bearings, so no need for "oil pressure". They are
supplied with oil mist (not liquid oil). I suspect they rely on
"centrifugal" catchers, possibly wind-back seals, also clever control of gas
pressures. There won't be anything deliberately rubbing for oil sealing
because of the speeds. To get the gas leakage down at blade tips they use
"abradable" seals which wear to a small clearance, but will cope with
transients without wrecking the blades.
Old Dec 10, 2010, 04:41 PM
David Littlewood
Guest
n/a Posts
Re: Gas Turbine oil seal question

In article <DtudnT_yBpbCy5zQnZ2dnUVZ8v6dnZ2d@bt.com>, Emimec
<emimec.19@NOSPAMbtinternet.com> writes

>Studying jet engines recently, it crossed my mind how is the oil "sealed" in
>the mainshaft. At the high RPM, I cant imagine it being a common oil seal
>like used on car engine crankshafts, and a total loss system sounds dubious
>to me for a modern engine. Anyone know ?
>Bob
>
>

Bob,

I have no personal expertise in this field, but I do have a book on
turbine engine design. It's from 1997, so reasonably current.

Apparently, most such engines use a dry sump system. Oil is filtered and
pumped under pressure to the bearings and gearboxes and other parts
requiring lubrication. A lube scavenge system draws oil from the sump,
passed through a detector to look for metal particles in the oil, and
then to a filter, heat exchanger and back to a reservoir tank.
Pressurised air from the compressor stage is bled into the appropriate
parts to prevent oil from leaking through seals, and also to cool the
sump to minimise degradation of the oil.

The oils used are totally synthetic (i.e. not simply derived from crude
oil) and have near-constant viscosity over the range of temperatures
encountered.

Not sue if this is a complete explanation, but it's pretty well all I
can add from a casual reading of the book's section.

David
--
David Littlewood
Old Dec 10, 2010, 08:15 PM
Jim Wilkins
Guest
n/a Posts
Re: Gas Turbine oil seal question

On Dec 9, 5:21 pm, "Emimec" <emimec...@NOSPAMbtinternet.com> wrote:

> Studying jet engines recently, it crossed my mind how is the oil "sealed" in
> the mainshaft. At the high RPM, I cant imagine it being a common oil seal
> like used on car engine crankshafts, and a total loss system sounds dubious
> to me for a modern engine.  Anyone know ?
> Bob


http://www.exxonmobil.com/lubes/exxo...14_JetEng2.pdf

jsw
Old Dec 13, 2010, 04:36 AM
John
Guest
n/a Posts
Re: Gas Turbine oil seal question

On Dec 10, 7:54 pm, Rusty Hinge <rusty.hi...@foobar.girolle.co.uk>
wrote:

> David Billington wrote:

> > I spent a couple of years living in Wichita Kansas and a guy I knew
> > there had dealt with British bikes in the past, he said the problem
> > wasn't with the engineering but with the assembly. He said if you took
> > the bike engine apart and put it back together properly then in his
> > experience they didn't leak.

>
> It's generally the primary chaincase - many of them were pressed steel
> and split vertically.
>
> The oil 'seal' was a 'V'-shaped rubber ring which went over the two
> halves, and a band of alloy channel which compressed the rubber when the
> ends were screwed together with a 3/16 BSF bolt at the back.
>
> The only way I ever found to keep that arrangement oiltight was to warm
> the chaincase and pour in a goodly quantity of hot paraffin wax.
>
> --
> Rusty


BL A series engines used to leak oil along with most british engines
of the era. Then the designers discovered negative pressure. Running
the crankcase below atmospheric pressure reduces oil leaks and
increases power due to lower internal wind losses. I really took this
idea to heart in my youth and connected my sump breather directly to
the inlet manifold. The reultant occasional gulp of oil/mayonaise
sludge made for a very effective smoke screen on the over-run. It once
managed to bring a complete dual carriageway to a crawl behind me. WW2
destryers had nothing on that car. I did learn better and redesigned
the system. After that, oil leaks reduced dratically.

John
 


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