I did a search for "Cankcase+Pressure" and got nothing, so started this thread. I guess it could be added into some of the others regarding oil breather, feel free to move as appropriate...
When I first flew with my new engine, an IO-375 in an RV7A, I had the Antisplat Aero oil separator with the vacuum system installed. After about 10 hours time on the engine it developed a small leak that I traced to the front seal, (oil on the ID of the flywheel).
I questioned Doug at Aerosport about this and he asked that I remove the Antisplat system and see of the leak would go away and sure enough it did. Doug felt that while the engine is breaking in there is just too much blow by for the system. Allen at Antisplat thought the system should work fine even during break in but since the leak went away after bypassing the system I was reluctant to try it again without measuring the crankcase pressure before and after installing the system to make sure I was not getting pressure that could cause a blown seal.
One of the problems may have been the check valve I was using. I purchased the NAPA unit and noticed it was pretty hard to blow through. At Allen's suggestion I purchased a high dollar unit made for the Chev Corvette (about $40.00 on ebay). It is definitely easier to blow through so maybe it will work better. Only measuring the pressure will tell for sure.
So out comes the trusty 0" to 15" WC Magnelic pressure gauge. I obtained a spare dip stick tube cap with no stick on it, drilled and tapped it for 1/8" NPT and ran a 1/8" tube through the firewall and then through one of those little chambers used on Cessna pito static systems, hoping it would dampen the pulsing enough to keep the needle on my Magnehelic gauge. I wanted to use an orifice fitting too but the hardware I had laying around did not work out. No problem with the gauge with the setup I used.
So the first measurement was done with a mostly normal breather setup. I have a 90 Deg. (oil filter clearance) fitting on a swivel and then a barbed fitting to allow silicone hose to route down close the the cowl exit, then it connects to aluminum tubing that routes out past the cowl opening exit a bit, also has the whistle slot in case of icing.
With that arrangement I was seeing pressure from 3" WC to 5" WC. In cruise flight sometimes it would go to zero, (maybe even some vacuum, I did not check it on the low side of the gauge). This was with the tube from the engine connected to the high side of the gauge, the low side just open to cabin air pressure with the vents closed.
Then I put the Antisplat system back on and measured again, of course, hoping for some vacuum, I connected the tube to the low side of the gauge.
At idle I got about 5" Vacuum.
During run up it went up to 10" WC, vacuum.
On Climb out at 2400 RPMs and around 22" MAP it showed between 10" WC and up to 15" at times.
In cruise at 10,500' it settled in around 12" WC vacuum.
I am happy with these numbers as they are a bit higher than I expected.
Even though I do have the 1/2 PSI pressure relief valve in place, I would like to monitor crankcase pressure on my engine monitor full time and have it alarmed at maybe the zero pressure or vacuum point. Perhaps that would provide good warning that the tube in the exhaust is getting plugged.
I had the pressure relief valve in place when I developed the leak and that has always puzzled me. With only 1/2 PSI the front seal should not have leaked, but at least now I have some data and I feel comfortable using the system again, but as I stated above, this would be a nice item to have displayed on my engine monitor. I happen to have an extra GM MAP pressure transducer that I may try out to see if it will be sensitive enough for this application, it is the same unit that Dynon uses for MAP measurement.
My thanks to Allen at Antisplat and Doug at Aerosport for working with me on this issue as I got great cooperation from both of them.
Randall in Sedona
When I first flew with my new engine, an IO-375 in an RV7A, I had the Antisplat Aero oil separator with the vacuum system installed. After about 10 hours time on the engine it developed a small leak that I traced to the front seal, (oil on the ID of the flywheel).
I questioned Doug at Aerosport about this and he asked that I remove the Antisplat system and see of the leak would go away and sure enough it did. Doug felt that while the engine is breaking in there is just too much blow by for the system. Allen at Antisplat thought the system should work fine even during break in but since the leak went away after bypassing the system I was reluctant to try it again without measuring the crankcase pressure before and after installing the system to make sure I was not getting pressure that could cause a blown seal.
One of the problems may have been the check valve I was using. I purchased the NAPA unit and noticed it was pretty hard to blow through. At Allen's suggestion I purchased a high dollar unit made for the Chev Corvette (about $40.00 on ebay). It is definitely easier to blow through so maybe it will work better. Only measuring the pressure will tell for sure.
So out comes the trusty 0" to 15" WC Magnelic pressure gauge. I obtained a spare dip stick tube cap with no stick on it, drilled and tapped it for 1/8" NPT and ran a 1/8" tube through the firewall and then through one of those little chambers used on Cessna pito static systems, hoping it would dampen the pulsing enough to keep the needle on my Magnehelic gauge. I wanted to use an orifice fitting too but the hardware I had laying around did not work out. No problem with the gauge with the setup I used.
So the first measurement was done with a mostly normal breather setup. I have a 90 Deg. (oil filter clearance) fitting on a swivel and then a barbed fitting to allow silicone hose to route down close the the cowl exit, then it connects to aluminum tubing that routes out past the cowl opening exit a bit, also has the whistle slot in case of icing.
With that arrangement I was seeing pressure from 3" WC to 5" WC. In cruise flight sometimes it would go to zero, (maybe even some vacuum, I did not check it on the low side of the gauge). This was with the tube from the engine connected to the high side of the gauge, the low side just open to cabin air pressure with the vents closed.
Then I put the Antisplat system back on and measured again, of course, hoping for some vacuum, I connected the tube to the low side of the gauge.
At idle I got about 5" Vacuum.
During run up it went up to 10" WC, vacuum.
On Climb out at 2400 RPMs and around 22" MAP it showed between 10" WC and up to 15" at times.
In cruise at 10,500' it settled in around 12" WC vacuum.
I am happy with these numbers as they are a bit higher than I expected.
Even though I do have the 1/2 PSI pressure relief valve in place, I would like to monitor crankcase pressure on my engine monitor full time and have it alarmed at maybe the zero pressure or vacuum point. Perhaps that would provide good warning that the tube in the exhaust is getting plugged.
I had the pressure relief valve in place when I developed the leak and that has always puzzled me. With only 1/2 PSI the front seal should not have leaked, but at least now I have some data and I feel comfortable using the system again, but as I stated above, this would be a nice item to have displayed on my engine monitor. I happen to have an extra GM MAP pressure transducer that I may try out to see if it will be sensitive enough for this application, it is the same unit that Dynon uses for MAP measurement.
My thanks to Allen at Antisplat and Doug at Aerosport for working with me on this issue as I got great cooperation from both of them.
Randall in Sedona
