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01-11-2020, 08:28 AM
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Join Date: Aug 2012
Location: Newnan, GA
Posts: 39
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sniffle valve required?
I have an RV 8 with an IO-360 injected motor. I bought the plane from the builder 7 years ago. At my recent condition inspection it was suggested that I install a sniffle valve on the bottom of the intake sump. That port is currently capped off with an AN fitting. This motor has 850 trouble free hours on it over the course of 17 years. My question is this - have I been lucky operating this motor or is the valve not really required. I realize it is used to drain the sump of residual fuel and or oil. If there is no drain does this fuel just get scavenged back into the intake system? I guess my point is why should I mess with success?
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Dave Romuald (FFC)
RV-8 655CL
RV-14 in work
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01-11-2020, 09:12 AM
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Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,351
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It is not required but it does help very much and it is a great addition for how little they cost or the ease of installation.
It helps drain the excess fuel in the sump when the engine is not running.
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Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
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01-11-2020, 09:14 AM
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Join Date: Jun 2005
Location: Georgetown, TX
Posts: 331
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It would be interesting to measure how much residual fuel, oil, stuff, has accumulated in that sump after all these years...
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Brian Decker
Retired Firmware Guy and Airplane Builder
2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231
Aided and abetted building a number of other RV's.
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01-11-2020, 09:28 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by bjdecker
It would be interesting to measure how much residual fuel, oil, stuff, has accumulated in that sump after all these years...
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Yep, next oil change when the engine is hot, take out that plug. If you feel lucky, don't put a pan under it. Mine drips sometimes, especially if flown rich and doing approach practices.
DanH does not have one either . . .
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Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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01-11-2020, 09:52 AM
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Super Moderator
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Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,626
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I've done inspections on those without them. Some nasty stuff comes out of that drain when the plug is pulled. It's a combinations of fuel and oil that drains back through the intake tubes when the engine is shut down.
Vic
__________________
 Vic Syracuse
Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
Kitplanes "Unairworthy" monthly feature
EAA Sport Aviation "Checkpoints" column
EAA Homebuilt Council Chair/member EAA BOD
Author "Pre-Buy Guide for Amateur-Built Aircraft"
www.Baselegaviation.com
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01-11-2020, 02:21 PM
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Join Date: Jan 2007
Location: Battleground
Posts: 4,348
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Probably should note to casual readers that a sniffle valve is for horizontal injection, not vertical.
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Smart People do Stupid things all the time. I know, I've seen me do'em.
RV6 - Builder/Flying
Bucker Jungmann
Fiat G.46 -(restoration in progress, if I have enough life left in me)
RV1 - Proud Pilot.
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01-11-2020, 02:59 PM
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Join Date: Oct 2006
Location: torrance, ca
Posts: 650
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I haven't had one in 13 years and 810 hours. Last CI I removed the intake tubes to replace the gaskets as I do about every other year (someday I'll install Ross' deal) and as usual there was no more than about a teaspoon of brown motor oil in the back of the plenum. No other "crud".
Also, this being a taildragger, all of that small amount of oil was in the back of the plenum, or several inches behind the sniffle valve boss, so even if there was a valve, nothing would have come out of it.
The only time I could think having a sniffle valve might be useful is IF the airplane were parked in a torrential rainstorm and somehow overwhelmed the drain hole in the fiberglass snorkel. Or if a guy forgot to drill that drain hole... Vic, in your myriad inspections, how many times have you found where there was no drain hole in that snorkel?
Last edited by hgerhardt : 01-11-2020 at 03:02 PM.
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01-11-2020, 08:54 PM
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Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,596
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Install it for a horizontal injected engine. It help prevents blowing out the air filter during a hot start.
Carl
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01-12-2020, 07:05 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Last time I looked in there, it was bone dry. Annual time right now; I'll look again. Not much need to guess, given most of us have some kind of tiny camera on a stick. Open the throttle and poke it in.
As I've written before, there are risks to not using a sniffle valve. The key risk is hydraulic lock...collecting enough liquid in the air plenum (fuel, oil, or water) to enable sucking up an incompressible quantity during cranking, or immediately after start. Risk adverse? Install a sniffle.
Both fuel and water evaporate in due course. They can't build up over time or cycles.
Oil has a very low vapor pressure, thus evaporates sloooooowly, and can potentially accumulate. However, I would think an engine which collects significant oil in the horizontal intake air plenum needs valve guide and/or ring work. Anybody collecting a quantity of oil in their updraft carb airbox? Same mechanics.
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Dan Horton
RV-8 SS
Barrett IO-390
Last edited by DanH : 01-12-2020 at 07:08 AM.
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01-12-2020, 07:20 AM
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Join Date: Aug 2005
Location: Dallas/Ft Worth, TX
Posts: 5,686
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The biggest danger is fuel pooling due to over priming/draining after shut down (hot start) and it has no where to go. if the engine backfires into that accumulated fuel it can literally blow off the intake sump or if you're lucky just blow out the air filter if the throttle is open enough to relieve the pressure.
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Walt Aronow, DFW, TX (52F)
EXP Aircraft Services LLC
Specializing in RV Condition Inspections, Maintenance, Avionics Upgrades
Dynamic Prop Balancing, Pitot-Static Altmeter/Transponder Certification
FAA Certified Repair Station, AP/IA/FCC GROL, EAA Technical Counselor
Authorized Garmin G3X Dealer/Installer
RV7A built 2004, 1700+ hrs, New Titan IO-370, Bendix Mags
Website: ExpAircraft.com, Email: walt@expaircraft.com, Cell: 972-746-5154
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