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  #1  
Old 07-23-2008, 06:49 PM
bjb3013 bjb3013 is offline
 
Join Date: May 2006
Posts: 68
Exclamation Sniffle Valve Question

I have a Lyc IO360-A1A 200 Hp with a sniffle valve that gets stuck open. It will close while cold but will not seal tight when hot. It will work when you blow through with your mouth but I think it requires to much vac to close. The idle is really bad with this leak. I can not richen up enough to make up for the leak and smooth the idle with the servo set correctly.
What is the down side to not having the valve in place. Will a normal check valve work? How about a auto pcv valve?

I noticed several Mooneys that had an open drain and a restrictor fitting with a hose. If I set the idle mixture on the servo correctly with the drain hose open will this be OK?

How much fuel can return to the plenum after shut down and shouldn't it be evaporated while the engine cools down. 100LL flashes off fast.

Thanks
BB
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  #2  
Old 07-23-2008, 07:55 PM
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flyeyes flyeyes is offline
 
Join Date: Jan 2005
Posts: 710
Default

Quote:
Originally Posted by bjb3013 View Post
I have a Lyc IO360-A1A 200 Hp with a sniffle valve that gets stuck open. It will close while cold but will not seal tight when hot. It will work when you blow through with your mouth but I think it requires to much vac to close. The idle is really bad with this leak. I can not richen up enough to make up for the leak and smooth the idle with the servo set correctly.
What is the down side to not having the valve in place. Will a normal check valve work? How about a auto pcv valve?

I noticed several Mooneys that had an open drain and a restrictor fitting with a hose. If I set the idle mixture on the servo correctly with the drain hose open will this be OK?

How much fuel can return to the plenum after shut down and shouldn't it be evaporated while the engine cools down. 100LL flashes off fast.

Thanks
BB
I can't speak to the alternatives, but a replacement sniffle valve is pretty cheap--I had to replace mine when I first ran my engine. IIRC it was maybe $9.

It was one of several things I did to chase down a rough idle.
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RV-8 flying
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  #3  
Old 07-23-2008, 09:02 PM
Bevan Bevan is offline
 
Join Date: Sep 2007
Location: BC
Posts: 717
Default Pardon my ignorance

Are we talking about a purge valve? or something else?

Bevan
RV7A but obviously no engine yet
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  #4  
Old 07-23-2008, 09:48 PM
JHines JHines is offline
 
Join Date: Jul 2007
Location: Rock Hill, SC
Posts: 390
Default

Not the same thing as a purge valve. Sniffle valve is a small check valve in the intake plenum, engine vacuum holds it closed while the engine is running and it opens by gravity when the engine is off, to let any fuel that collects in the intake to drain away.

A purge valve is typically user-controlled and used to recirculate fuel thorugh the FI system back to the tank, to replace hot fuel with colder fuel and hopefully prevent vapor lock.
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Charlotte, NC
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  #5  
Old 07-23-2008, 10:21 PM
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hgerhardt hgerhardt is offline
 
Join Date: Oct 2006
Location: torrance, ca
Posts: 276
Default Do you really need one?

How many here actually HAVE a sniffle valve on their horizontal induction IO's? If you look in the Lycoming parts manual, most of the IO's did NOT come with one from the factory, including my IO-360-A3B6D. I never installed one either, and after 144 hours of flying my -6, don't seem to need one. I've never had a hot start that didn't start because of flooding. Just crank with the mixture in cut-off until it fires.

Of you guys that have one, do you ever see fuel come out of the thing? At least more than a few drops?

Heinrich Gerhardt
RV-6, flying
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  #6  
Old 07-23-2008, 11:34 PM
Aden Rich Aden Rich is offline
 
Join Date: Jan 2005
Location: Port Angeles, Wash
Posts: 293
Default Your asking for trouble

I have a sniffle valve on my IO-360-M1B engine. It gets rid of the gas in the sump. However, in the RV taildraggers the port is in the wrong spot. There is about a 1/2 cup of gas in there sitting pooled up in the taildragger mode. Have a hiccup and your sump might be toast. I have talked to several people including the owner of my RV-6 who have had problems with hot starts and blew up the fiberglass snorkle. It was easily repaired but we decided to drill a hole in the back part of the sump and put a drain fitting to have the sniffle valve there. It has worked well and improved hot start issues.
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  #7  
Old 07-24-2008, 10:54 AM
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Noah Noah is offline
 
Join Date: Jun 2007
Location: RI
Posts: 780
Default Disassembly and troubleshooting - piece of cake

I just disassembled and cleaned the sniffle valve on my IO-360 A1B6 200 hp engine as part of its overhaul. Recommend you do the same - there's a snap ring to remove, then a disc (looks like phenolic). If the valve isn't functioning correctly, the problem should be readily apparent when you take it apart, as this valve's function is very simple. Perhaps you could get a replacement disc from aero or elsewhere if its not serviceable. If the seat is damaged you may need to replace the valve, but I don't think these are terribly expensive.
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  #8  
Old 07-24-2008, 02:19 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Cupertino, CA
Posts: 1,191
Default thanks for bringing this up!

Quote:
Originally Posted by bjb3013 View Post
I have a Lyc IO360-A1A 200 Hp with a sniffle valve that gets stuck open. It will close while cold but will not seal tight when hot. It will work when you blow through with your mouth but I think it requires to much vac to close. The idle is really bad with this leak. I can not richen up enough to make up for the leak and smooth the idle with the servo set correctly.
What is the down side to not having the valve in place. Will a normal check valve work? How about a auto pcv valve?

I noticed several Mooneys that had an open drain and a restrictor fitting with a hose. If I set the idle mixture on the servo correctly with the drain hose open will this be OK?

How much fuel can return to the plenum after shut down and shouldn't it be evaporated while the engine cools down. 100LL flashes off fast.

Thanks
BB
I'm glad you asked this. And thanks for all the good answers. I am installing an IO-360-A1A in an RV-8, and the Lycoming parts catalog shows that the -A1A doesn't use a sniffle valve, but the -A1B6 does. It seems like a good idea, though, so I bought one (not very expensive), but I was wondering about all the things you asked.

The -A1A sump has the port for it toward the back, so I think it will drain OK while sitting on the tail. But I also wonder how much ever actually drips out?

Also, what about wide-open throttle when there is virtually no manifold vacuum - IN FACT, with an unfiltered ram-intake at cruise, the pressure in the plenum is probably higher than the pressure in the lower cowl area - won't that open the valve and leak intake air?

Steve
RV-8QB FWF

Last edited by scsmith : 07-24-2008 at 02:22 PM. Reason: added question
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  #9  
Old 07-24-2008, 03:10 PM
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David-aviator David-aviator is offline
 
Join Date: Feb 2005
Location: Troy. Missouri
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Quote:
Originally Posted by scsmith View Post
.....But I also wonder how much ever actually drips out?

Steve
RV-8QB FWF
In chatting with Larry Vetterman about exhaust systems we got on the subject of the sniffle valve. If the valve is used make sure it does not drip on a red hot exhaust pipe after shut down.
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  #10  
Old 07-26-2008, 12:52 PM
DSmith DSmith is offline
 
Join Date: Feb 2006
Location: Panama City Beach, FL
Posts: 89
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On tail draggers especially this valve is a must for horizontal intake sumps. If the aircraft is left out in a heavy rain the water can run down the snorkle and into the sump which can cause hydraulic lock when you next try to crank up that bad boy. In my opinion the accumulation of fuel maybe the lesser of the two problems. Some of the sumps have a lower level where the valve is installed and the water would accumulate. Van sell the sniffle for $44.00.
Danny
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