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Raven invert system

frankh

frankh

Well Known Member
Morning all.

I have a problem that appears to be getting worse and with the annual coming Up I really need to address it.

A couple of years ago I noticed that the oil pressure would dip when I applied full power..For example if I was doing a missed approach the oil pressure would be sitting at say 65psi on the glide (12" mp, low RPM), then drop to 45 to 50psi as I applied full power (2700RPM). This would happen for a few seconds then recover to 65psi at full power. I didn't do anything about it, but have been "keeping an eye on it".

This problem appears to be getting gradually worse and with the annual due its probably time to look into it. I did pull the horizontal suction screen about two years ago and notice that the 45 deg adjustable take off did not have a set screw it was free to rotate (although the hose prevented this from happening)

I am wondering if the slight movement of the adaptor has caused a small air leak (parts fretting slightly) and this is causing the the pressure to drop as it the pump is suddenly forced to increase speed.

I am thinking of first of all getting a new set screw and locking in place plus slathering some RTV over the fitting to plug any leaks..I guess I could also by pass the oil valve if that didn't fix it.

This has been a "feature" since day 1 and I noticed the oil pump would always lose its prime if the engine was left to sit overnight. I "cured" that by fitting an accumulator.

Thoughts?

Thanks

Frank RV7a IO360
 
My first guess would be the oil valve needs cleaning. If it is not sealing off the upper port, that would be where the air could be coming from during normal flight. Just a thought.
 
Last edited:
Good point

if that upper valve was not sealing that would certainly explain the loss of pump prime too

Frank
 
Actually Alton

I could isolate the invert valve completely by removing the "upside down hose" and plugging both ends with a cap from the local hydraulics store...If the problem is still there it will be a problem in the hose or suction screen.

Frank
 
Funny you should ask

Just today I found time to plug the invert hose with a plug and cap. $5 of parts from the local hydraulics emporium.

I had to take the cowl off and pull out my accumulator so it was a lot more work than I anticipated so by the time I was ready to test it was already dark.

I thought it prudent to do such testing in daylight.

Anyway, the invert hose is now plugged off ready for test #1..i.e is the invert valve sucking in air through the valve.

Hopefully tomorrow morning I will have the answer..:)

if its not that then I note that two of my hose fittings have "O" rings to allow for movement. Its not impossible one of those could be sucking air through..If so I will wipe some silicone around the joints and re-test.

Frank
 
Test #1 Negative

Namely the oil pressure still drops on takeoff with the invert valve top port plugged (I have a penum but din't quite pick up the courage to fly it without the cowl).

But at full Power (which for right now I am assuning is simply related to RPM) the oild pressure drops from 75 to 40 psi momentarilly.

I note I do not have a restircor in my oil guage line so its more noticable than it otherwise might be.

Even so its not normal.

I have now silicone gooped the "o" ring joints in my oil feed lines.

If this is neagtive I will investigate temporarily removing the invert system altogether.

I think this "should" simply be a case of pulling the blanking plug at the end of the horizontal screen and capping off the hole.

But I'm not certain on this..Anyone advise?

Frank
 
Didn't you have to trim the screen as part of the install? Can you go without? I cant remember, it has been a couple years since i installed mine.
 
More thoughts

I think you could go without a screen tmeporarily, but I would rather not.

Aproblem I had with my thought experiment was that an air leak on the inlet side to the oil pump would not explain losing prime on the oil pump over night.

Well actually it does...Its not that the pump looses prime sitting in the hangar, its a case of when the oil cools down its nice and thick. Thus when the engine is started the pump has to suck extra hard to move the oil.

that extra suck could easily intorduce a lot more air to the suction side of the pump, thus airlocking the pump.

So all the symptoms can now be explained by an inlet side air leak.

later today I will test the fittings that have been gooped up with silicome on the outside over night.

Frank
 
Frank,

I don't think you can fly without the scavenge filter as it holds in the plug that reverses the flow through the screen. Have you checked that the O-ring in the plug is in good condition? You will need a long bar with a 10-32 thread on the end to get the plug out. The system I had with a 45? fitting on the sump (although it was a Christen rather than Raven) used a jam nut, and a regular crush gasket, on the fitting to keep it in place.

Sounds like the flow to the pump is insufficient at max rpm? Do you have constrictions in any of the oil scavenge hoses?

Pete
 
Found it

It actually was a combination of two things.

The smaller issue was there was a small air leak on the suction side during start up..this would show up as the pump having been airlocked after it went cold...The thick oil causes major suck and the O ringed swivel hose end fitting was probably leaking a little air.

I tested this by leaving over night and sealing the fitting up with silicone..Pump did not air lock and pressure came up within 2 seconds of the engine firing.

The bigger issue was I run the oil level around 6 qts and had let it fall to about 5 qts...The take off is right at the front of the sump..The acceleration caused to port to be uncovered and dropped the oil pressure..duh!

Put two qts in and the problem was solved on take off..will need to cowl up the engine and take it flying to be sure.

At the next oil change I will remake the hose with a non swivelling fitting.

Frank
 
Thanks

Yes its been bugging me ever since I finished the airplane. I thought it wise to document the whole thing so if someone else has the same problem in the future they can review my notes.

I almost wish it was oil change time so I could get to fixing it once and for all..:)

Frank
 
Hi Frank, Keep me posted I have a 6 with inverted system, the swivel always leaks (Raven or Christian) Let me Know how the fixed fitting works (washer adjust) now that its set up it works OK . Where did you put your breather for the slobber pot? I have mine plumbed down the gear leg (angle was critical)
Peter RV6.2

frankh said:
Yes its been bugging me ever since I finished the airplane. I thought it wise to document the whole thing so if someone else has the same problem in the future they can review my notes.

I almost wish it was oil change time so I could get to fixing it once and for all..:)

Frank
Click to expand...
 
Swivel

I need to be careful in referring to which swivel.

The swivel that was leaking was a speed sop hose end that comes with an O ringed joint.

The ajustable 45 degree take off at the sump I don't believe was leaking.

As the hose end is subject to movement and there is possible fretting going on I want to replace this hose end with a non swivelling version.

Frank
 
Quick question Frank. When you made up the hoses, including the swivel one, were they pressure tested? I'm installing a Raven too and may have to fit a swivel on the suction (side port on cold air induction sump opposite screen 45 swivel) due to a sump bolt housing interfering with a 90 suction fitting. So I need a straight suction fitting but without a 90 swivel I will have a very long hose - that said there will be one less place for a leak.

Thanks for logging the fault and cure - most helpful.

Regards


Bob
www.rv-8.co.uk
 
Bob Ellis said:
Quick question Frank. When you made up the hoses, including the swivel one, were they pressure tested? I'm installing a Raven too and may have to fit a swivel on the suction (side port on cold air induction sump opposite screen 45 swivel) due to a sump bolt housing interfering with a 90 suction fitting. So I need a straight suction fitting but without a 90 swivel I will have a very long hose - that said there will be one less place for a leak.

Thanks for logging the fault and cure - most helpful.

Regards


Bob
www.rv-8.co.uk
Click to expand...

No Bob I didn'r pressure test them and to be honest there is no real reason to do so. remember the hoses are under vacuum all off the time and leaking air is a different situation, mainly because the swivel is sealed with an o ring. I.e the leak I believe has shown up after the hose has been in service for some time. I was nervous about using a swivelling hose end and there are non swivelling versions of the same hose end so i will be changing to those at some point. Its only two hose fittings after all.

The 45 degree ajustable fitting that raven sells... I don't believe has been leaking..but if you have the opportunity of not having it then even better.

As to hoses I ordered mine from Summit racing..You need to order the hose with the partial inner steel braid..This is what stops the hose collapsing under vacuum..Its a pretty good hose and I have heard of Aeroquip 303 (megga spendy so called high quality) hose collapsing under vacuum.

Cheers

Frank..Ex pat Brit living in Oregon.
 
Hi Frank

My pressure test comment wasn't a criticism, I was intimating that a leak is a leak whether it is under pressure or a vacuum, and I will test mine just for peace of mind. I get the point that the leak was not the hose but the swivel fitting o-ring and I will obtain a non-swivel 90 fitting. I have already sourced Aeroquip 601 from ACS using the Christen parts manual as a reference, this hose has the partial inner braided steel that you referred to - $$$$ but worth it I think for peace of mind and resale.

Regards

Bob
 
No offense taken

Bob Ellis said:
Hi Frank

My pressure test comment wasn't a criticism, I was intimating that a leak is a leak whether it is under pressure or a vacuum, and I will test mine just for peace of mind. I get the point that the leak was not the hose but the swivel fitting o-ring and I will obtain a non-swivel 90 fitting. I have already sourced Aeroquip 601 from ACS using the Christen parts manual as a reference, this hose has the partial inner braided steel that you referred to - $$$$ but worth it I think for peace of mind and resale.

Regards

Bob
Click to expand...
I didn't take your question as a criticism..I'm not sure i agree a leak is a leak though either..i mean certainly getting a hose pressure tested is not harmful so if it gives you peace of mind then why not?

I think the or ring leaked under vacuum but I doubt it would would have leaked under pressure..But I can't prove that of course.

As for using 'proper" hoses adds to resale value..maybe, I guess it depends on the attitude of the prospective buyer. If it were me i would take one look at the steel inner braid of the spare hose I had and not think twice about it.

On the other hand I am sure there are some buyers who would never buy an airplane if the hoses were assembled by the builder no matter what the makers name is printed on the outside.

Frank
 
Followup

I did hear back from Bob at raven.
He told me that ideally the oil pick up should be at the back RH corner of the sump and not the front RH corner as is the case on my FF sump.

In order to achieve this happy state I would have to pull the sump and weld on a 1/2" boss..To be honest that looks like an awful lot of work to achieve the perfect solution so I doubt I'll bother.

If your building one now though it might be worth considering.

Frank
 
Flight test

I have finally got around to flight testing the issue.

The surging issue was resolved by keeping the min oil level at 6 qts.

Interestingly the cruise oil pressure had fallen to 55psi..I have now siliconed up the suspect leaking swivel hose end and the cruise oil pressure has jumped up to 75psi hot (although it was about 10 to 15 degrees cooler than Summer oil temp).

It looks like the O ring was leaking a little air under almost all conditions and will be changed at the next il change.

Frank
 
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