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-   -   sniffle valve required? (https://vansairforce.net/community/showthread.php?t=178538)

dromuald 01-11-2020 08:28 AM

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?

Bavafa 01-11-2020 09:12 AM

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.

bjdecker 01-11-2020 09:14 AM

It would be interesting to measure how much residual fuel, oil, stuff, has accumulated in that sump after all these years...

BillL 01-11-2020 09:28 AM

Quote:

Originally Posted by bjdecker (Post 1399150)
It would be interesting to measure how much residual fuel, oil, stuff, has accumulated in that sump after all these years...

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 . . .

vic syracuse 01-11-2020 09:52 AM

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

JonJay 01-11-2020 02:21 PM

Probably should note to casual readers that a sniffle valve is for horizontal injection, not vertical.

hgerhardt 01-11-2020 02:59 PM

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?

Carl Froehlich 01-11-2020 08:54 PM

Install it for a horizontal injected engine. It help prevents blowing out the air filter during a hot start.

Carl

DanH 01-12-2020 07:05 AM

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.

Walt 01-12-2020 07:20 AM

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.

DanH 01-12-2020 09:46 AM

Explosion risk is a function of fuel-air ratio by weight. Fuel in liquid phase has no practical explosion risk. The fuel of interest is that which is in vapor phase, above the liquid, and combined with air in a proportion within the combustible range.

Put another way, the risk is about the same for two tablespoons of fuel in the air plenum, or a quart.

Correction: See post #57, this thread. The quart is less risky.

scsmith 01-12-2020 01:26 PM

Quote:

Originally Posted by DanH (Post 1399360)
Explosion risk is a function of fuel-air ratio by weight. Fuel in liquid phase has no practical explosion risk. The fuel of interest is that which is in vapor phase, above the liquid, and combined with air in a proportion within the combustible range.

Put another way, the risk is about the same for two tablespoons of fuel in the air plenum, or a quart.

Except that if there is an ignition event in the vapor-filled plenum, the pooled liquid will pretty quickly vaporize and contribute.

I have a sniffle valve for the main concern being that even a fraction of a tablespoon of liquid drain-back, then vaporized by the warm sump and filling the plenum, could get ignited on a subsequent start. Think about a fuel stop or quick turn dropping off a passenger.

I don't know how likely it is. I have had one backfire on a hot start, and I kept cranking, sucking the fire back into the engine.

It is less than ideal for taildraggers that the sniffle valve boss is not along the back edge of the plenum. But at least that limits the volume of liquid that can pool, then evaporate.

DSmith 01-12-2020 02:11 PM

Water in the sump is a real exposure if you tie down on the ramp and there comes a heavy blowing rain storm. A friend of mine had that happen to him while on a trip. Fortunately the hydraulic lock was not catastrophic due to a weak battery and the fact he recognized the problem quickly.

Sniffle valves are cheap and good insurance.

jcarne 01-12-2020 05:12 PM

I have heard a few people mention now that these sniffle valves are cheap. Is there an alternative that I am not aware of? Spruce is selling the valve right now for $115. Cheap in the grand scheme of things but not cheap for what it is.

RV8Squaz 01-12-2020 06:15 PM

Quote:

Originally Posted by hgerhardt (Post 1399222)
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?

Torque,

My experience in 1700 hours and 13 years has been exactly as described above, except I think I had a 1/4 teaspoon of oil along the back of the sump. I don't see how a sniffle valve would help in the ground attitude of a taildragger unless there was severe flooding with either water or fuel. I guess it can't hurt, but I haven't experienced a need for it.

DanH 01-13-2020 06:37 AM

Quote:

Originally Posted by scsmith (Post 1399410)
Except that if there is an ignition event in the vapor-filled plenum, the pooled liquid will pretty quickly vaporize and contribute.

Enclosed space. Where is the required oxygen?

Quote:

I have a sniffle valve for the main concern being that even a fraction of a tablespoon of liquid drain-back, then vaporized by the warm sump and filling the plenum, could get ignited on a subsequent start.
No matter, as our sumps are designed are to be unharmed. For sure a sniffle doesn't prevent the occasional "thump from the sump", or air filter blowouts. Most of the cranking fires I've seen (two maybe) were flooded engines with fuel dripping on the ground prior to the prop turning. The average sniffle valve installation dumps fuel inside the cowl or just aft of it. Plenty of air there.

Quote:

Originally Posted by DSmith (Post 1399418)
Water in the sump is a real exposure if you tie down on the ramp and there comes a heavy blowing rain storm. A friend of mine had that happen to him while on a trip. Fortunately the hydraulic lock was not catastrophic due to a weak battery and the fact he recognized the problem quickly.

Sniffle valves are cheap and good insurance.

Agree.

I note another thread going right now, in which the OP (apparently not the builder) doesn't seem to know what he does or doesn't have, or to have been aware of water risk. Plus, an unskilled operator could just as easily hydraulic lock one with excess fuel. Although many of us successfully operate without a sniffle, henceforth I'll probably recommend their use, just because so many RV's are now in the hands of non-builders.

rv8ch 01-13-2020 07:15 AM

sniffle
 
Quote:

Originally Posted by DanH (Post 1399626)
... Although many of us successfully operate without a sniffle, henceforth I'll probably recommend their use, just because so many RV's are now in the hands of non-builders.

I agree - it would be interesting to know that number - it's almost certain that the percentage will get closer and closer to 100%.

scottmillhouse 01-13-2020 10:09 AM

Interesting that most folks do not use one. It appears to be specified by both Vans and Lycoming. I only have a little more than 40 hours since new but I’m still getting some fuel and oil mixed draining out after most flights. Generally about a teaspoon. For those with sniffle valves, is this normal?

I guess I exaggerated the amount as a teaspoon, as others noted a 1” drip spot most days is probably about what I see too.

flyinga 01-13-2020 10:50 AM

Scott,
I often get a mall amount of fuel/oil out of my sniffle valve. Usually only a drop or two. Makes about a 1" dia. spot on hangar floor.

DanH 01-13-2020 10:54 AM

Both you guys are using a constant flow injection without a purge valve?

bob woods 01-13-2020 02:00 PM

Sniffle valve
 
I bought mine from airflow performance. They call it a manifold drain. $ 25.00

jcarne 01-13-2020 02:29 PM

Quote:

Originally Posted by bob woods (Post 1399781)
I bought mine from airflow performance. They call it a manifold drain. $ 25.00

Oh I see, hmmm.

Can someone confirm whether it is just a simple brass fitting with a hole in it? If that is the case there is no way I'm going to give Lycoming 115 bucks for one. The one from Airflow Performance just looks like a simple AN flare to NPT fitting.

The Lycoming one found here looks like it has a check valve function to it too.

SmilingJack 01-13-2020 02:46 PM

I bought a piper sniffle valve that has a 90 right Angle drain.

I can?t find the p/n at the moment.

wilddog 01-13-2020 02:46 PM

The one that came with my Titan is a check valve.

DanH 01-13-2020 03:04 PM

Quote:

Originally Posted by jcarne (Post 1399785)
Can someone confirm whether it is just a simple brass fitting with a hole in it?

It is not. It's a check valve. It seals at low manifold pressure, but could just as well be an open fitting at WOT, given a good ram inlet.

flyinga 01-13-2020 03:19 PM

Dan,
To answer your question: yes. Constant flow with no purge valve.

jcarne 01-13-2020 07:46 PM

Thanks guys, you just saved me 100 bucks. After some research I see the one that Airflow Performance sells is indeed a check valve, will be ordering soon.

ronschreck 01-14-2020 05:25 AM

Quote:

Originally Posted by jcarne (Post 1399867)
Thanks guys, you just saved me 100 bucks. After some research I see the one that Airflow Performance sells is indeed a check valve, will be ordering soon.

Jeeeze! Where were you last week when I ordered a sniffle valve from Vans for $120. :mad:

I have been running without a sniffle valve ($120) or manifold drain ($25) for 14 years and over 2200 hours with no problems. I have an Airflow Performance fuel injection with a purge valve. I just installed a sniffle valve because it was noted as "missing" by the well-respected A&P who just did the pre-buy inspection for the person who is buying my RV-8.

I'm not making any judgement about the wisdom of having a sniffle valve, just relaying my experience. When I removed the sump plug to install the valve there was nothing draining from the hole. I am curious to know why the inlet to the sniffle valve is about 1/16 inch diameter and the outflow port is 1/4 inch in diameter! Seems like the slightest bit of crud would render it more useless than it already seems to be.

Sniffle Inlet

Sniffle Outlet

DanH 01-14-2020 08:23 AM

Quote:

Originally Posted by flyinga (Post 1399806)
Dan,
To answer your question: yes. Constant flow with no purge valve.

Then it is common to see a bit of fuel in the air plenum, and from the sniffle.

The engine driven pump creates line pressure by pushing a diaphragm with a big spring. The engine's pump cam (via the pump pushrod and pump lever) compress the spring, then rotates out of the way, leaving the spring free to push the diaphragm.

Now shut down the engine using the mixture control. If the engine stops with the pushrod on the pump cam's base circle, the pump spring is free to push, and 25~30 psi remains applied to the servo inlet. The only thing preventing flow is the mixture disc valve....which has a leak rate. The rate is small, but it's there; it is not a zero flow valve. The leak sends fuel to the divider, onward to the nozzles, into the manifolds. Some of it runs down to the sump plenum. For the most part, the leak rate is offset by evaporation rate, and the difference is minimal.

The disc valve is common to the Bendix RSA and its variations, like the current Avstar controller, and late model Airflow Performance FM-150. Those of us using a "classic" Airflow Performance controller like the FM-200 have a drum type mixture valve. It has a much higher leak rate (1 to 3 lbs per hour) and would rapidly dump fuel into the manifolds in the above scenario. So, AFP units with drum valves also get a purge valve. When opened, the purge valve re-routes fuel from the control, before it reaches the divider, and sends it back to a tank. In consequence, purge valve users see less fuel in the manifolds after shutdown. It's limited to the very small amount which may boil out of the divider and spider lines. That happens with both mixture valve types, purge or no purge.

Anyway, the much reduced fuel dump is why purge valve users see less need for a sniffle.

BTW, a purge valve can be installed with any fuel control. The reason for its existence is per the above, but the serendipitous feature most loved is the ability to flow a large quantity of cool fuel through the entire system prior to cranking.

jcarne 01-14-2020 09:55 AM

Quote:

Originally Posted by ronschreck (Post 1399926)
Jeeeze! Where were you last week when I ordered a sniffle valve from Vans for $120. :mad:

I have been running without a sniffle valve ($120) or manifold drain ($25) for 14 years and over 2200 hours with no problems. I have an Airflow Performance fuel injection with a purge valve. I just installed a sniffle valve because it was noted as "missing" by the well-respected A&P who just did the pre-buy inspection for the person who is buying my RV-8.

I'm not making any judgement about the wisdom of having a sniffle valve, just relaying my experience. When I removed the sump plug to install the valve there was nothing draining from the hole. I am curious to know why the inlet to the sniffle valve is about 1/16 inch diameter and the outflow port is 1/4 inch in diameter! Seems like the slightest bit of crud would render it more useless than it already seems to be.

I hear ya, I have delayed buying that bad boy for a bit now as it just seemed way overpriced to me; like certified market overpriced. :D

rmartingt 01-14-2020 10:00 AM

Based on the above, does anyone see a need for a sniffle valve on an EFI engine? I would expect fuel leakage to be minimal on shutdown, especially if it's done by killing the pump or ECU power.

DanH 01-14-2020 10:35 AM

The risk of water ingestion remains with a horizontal induction and any fuel system choice.

As for EFI, I have seen a bent connecting rod taken from a GM 6.0L, attributed to hydraulic lock after a defective injector dumped into the cylinder. Do the currently available EFIs hold line pressure after shutdown?

vic syracuse 01-14-2020 04:50 PM

I was short on my earlier reply on this thread as I was really busy with something. Sorry.

I don?t mean to sound blunt but I don?t understand risking the engine and perhaps the airplane for a $100 part. We install these valves on about half of the non-builder owner airplanes that come through our shop, because they don?t have one installed. A lot of gunk and nasty stuff tends to come out of the intake when the drain plug is pulled to install the sniffle valve.

Where does it all come from you ask? Well it is a combination of a lot of things. First, any rainwater that gets into the intake when it is parked will run down the intake and carry some dirt and debris with it. And that water will sit there and pool if the rain is heavy enough, and may not evaporate prior to you trying to start the engine. Meaning there is the potential for a nice big slug of water to get sucked up and potentially cause a hydraulic lock. Want to understand the potential damage of a hydraulic lock? Read my story in KP this past summer on losing the engine in my stearman which was most likely due to a past hydraulic lock. The damage may not manifest itself for a while.


Second, Fuel drains into the cylinders from the injection system after shutdown, which over time just dries up and cakes with the rest of the dirt.

Third, sometimes there is oil leakage past the intake valves into the intake tubes, which just adds to the mess.

Lastly, on a flooded engine start, the fuel pools in the intake. Run the battery down while cranking and the potential for a backfire into the intake is a very distinct possibility. I have seen more than one crinkled filter on RV?S due to this scenario. I have also seen the damage done to the intake system from a backfire.

Not trying to preach. Just trying to share from experience. I know there are some of you who say their airplane has been running for such and such hours and has no problem. Great. I am trying to share the experience from looking at over one thousand RV?s now and hope it helps you with your decision making. 😀

Toobuilder 01-14-2020 05:45 PM

Quote:

Originally Posted by DanH (Post 1400009)
... Do the currently available EFIs hold line pressure after shutdown?

Mine does. Not the full 45 -50 working pressure, but it will hold 15+ PSI for several days.

ronschreck 01-15-2020 04:05 AM

Quote:

Originally Posted by vic syracuse (Post 1400107)
A lot of gunk and nasty stuff tends to come out of the intake when the drain plug is pulled to install the sniffle valve.

Where does it all come from you ask? Well it is a combination of a lot of things. First, any rainwater that gets into the intake when it is parked will run down the intake and carry some dirt and debris with it. And that water will sit there and pool if the rain is heavy enough, and may not evaporate prior to you trying to start the engine.


Second, Fuel drains into the cylinders from the injection system after shutdown, which over time just dries up and cakes with the rest of the dirt.

Third, sometimes there is oil leakage past the intake valves into the intake tubes, which just adds to the mess.

😀

Vic,

If all this collected mess can gather in the sump why is the intake of the sniffle valve only 1/16 inch in diameter? It seems it would get clogged up very easily.

(BTW, I have not had any issues over 14 years and 2200+ hours without a sniffle valve but my experience does not necessarily indicate that there is no need for one. I do have a purge valve and a water drain hole and that may account for my positive experience. At any rate, I have now installed a sniffle valve and even at $120 consider it cheep insurance.)

vic syracuse 01-15-2020 04:47 AM

Quote:

Originally Posted by ronschreck (Post 1400195)
Vic,

If all this collected mess can gather in the sump why is the intake of the sniffle valve only 1/16 inch in diameter? It seems it would get clogged up very easily.

(BTW, I have not had any issues over 14 years and 2200+ hours without a sniffle valve but my experience does not necessarily indicate that there is no need for one. I do have a purge valve and a water drain hole and that may account for my positive experience. At any rate, I have now installed a sniffle valve and even at $120 consider it cheep insurance.)

Most of it drains right after shutdown. Those with sniffle valves will usually see a drop or a puddle at the exit after shutdown.

Consider this?? the plans for the FAB box which is used in vertical draft intake systems call for drain holes for the very same reasons I mentioned in my post last night. Why would we NOT have drain holes in the intake of the horizontal intake systems????

Vic

DanH 01-15-2020 07:32 AM

Quote:

Originally Posted by vic syracuse (Post 1400197)
Most of it drains right after shutdown. Those with sniffle valves will usually see a drop or a puddle at the exit after shutdown.

Tell us about the exit. Intake water is one thing, but I assume you don't approve of dumping priming fuel into the lower cowl.

Sometimes a sniffle drain can be tricky. Here's an example, circa 2012, my own airplane.



That's an AFP sniffle coupled to a steel line. Why steel? Because the identical aluminum line broke in not very many hours. Why aluminum? Because I went through several flex lines, all of which would not withstand the radiant heat from the 4-into-1 exhaust. Got hard and cracked, melted, whatever.

The kicker? Despite fixation of the aft end of the line, engine shake vs the mass of the steel line broke the aluminum sniffle at the cross pin hole. That's when I thought about it and decided to experiment with no sniffle at all.

I did consider making a sniffle valve using a right angle AN fitting as the basis. I think Mooney used a right angle sniffle. They are just a little ball and a retainer pin. Might still do it, as it would allow running a line directly aft. Maybe Don Rivera would add it to his parts list.

Quote:

Consider this—— the plans for the FAB box which is used in vertical draft intake systems call for drain holes for the very same reasons I mentioned in my post last night. Why would we NOT have drain holes in the intake of the horizontal intake systems????Vic
I think most of the horizontal induction guys do have drain holes in our airbox or snorkel, although a few builders miss it. I do for sure, and designed the airbox with rainwater in mind.



Thread title is "Sniffle Valve Required". The strict answer is no. However, it's not a trivial decision, and we agree it is good insurance.

William Slaughter 01-16-2020 08:23 AM

Quote:

Originally Posted by DanH (Post 1400217)
Tell us about the exit. Intake water is one thing, but I assume you don't approve of dumping priming fuel into the lower cowl.


I too would like to hear about the exit. I have a sniffle valve, but have been operating without it because I couldn't see a reasonable way to route the drain overboard. I have the same 4:1 exhaust as shown by Dan.

ronschreck 01-20-2020 01:24 PM

A word from an expert...
 
This is an interesting thread and I thought it wouldn't be complete without hearing from Don Rivera who is the owner of Airflow Performance and probably knows more about fuel injection systems than anyone I can think of.
So I asked Don if he would mind adding to the VAF corporate knowledge of the sniffle valve. His reply:

Hi Ron,

If you are running a forward facing sump then a "sniffle valve" (manifold drain) should be standard equipment. You have been operating a FM-200 that was built in 1996 which has a purge valve. Using the purge valve correctly to start and stop the engine would preclude getting excess fuel in the engine during a start or shut down. The emphasis here is using the purge valve correctly. You apparently understand the operation of the FM-200 and the proper use of the purge valve. We find that many customers that have fuel controls with purge valves do not use them as intended, in which case may cause excess fuel to drain down the intake pipes into a horizontal sump. This is where the manifold drain would come into play and drain off the excess fuel overboard. Today we sell mostly units that do not require the purge valve, so people do not have to know that operational aspect. But it's probably a good idea to install a manifold drain on any horizontal sump engine whether it has a purge valve or not.

N49ex 01-20-2020 04:03 PM

For what it's worth, my I/O-390 sniffle drops anywhere from nothing to a teaspoon per flight, mostly trending to the minimal. But, it's messy in any case, so my valve hose terminates in a small couple ounce bottle which I dump at oil changes. Keeps the hanger floor cleaner!


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