Sniffle valve dribbles

[Randy]

RV7A, IO-375, Cold air horizontal induction, Precision/Eagle injection system came with the engine from Aerosport.

Around 5 to 10 minutes after shutting down, the tube coming from the sniffle valve will begin dripping fuel, sometimes with oil in it, on the ground making about a 6" diameter blue circle. This gets embarrassing when you visit someone and they have to run after a drip pan to protect their nice clean concrete pad in front of their hangar as happened to me this last weekend. Sorry Rosie!

I have talked to Precision Airmotive, Aerosport, at Don and AFP about this problem. I have tried the suggested shut down method where I run the engine up to around 1500 RPMs before shutting down, then pull throttle back to idle and quickly follow that with mixture back to idle cutoff. This is supposed to clear out the excess fuel in the intake tubes. This did not help.

I do get a good clean engine shut down when pulling the mixture back to idle cutoff.

I understand that the mechanical fuel pump will pump an extra stroke when the engine is shut down, and this fuel just flows through the system and into the intake ports above the intake valves.

On the cold air horizontal intake manifold this fuel will collect right at the sniffle valve and flow out on the ground. On a vertical injection system, this same fuel might be flowing out the servo, pooling in the air filter box rather than out on the ground.. Can anyone verify this?

At the ice cream social fly in last weekend my RV was the only one out of 40 plus RVs that was dribbling fuel on the ramp. Gotta fix it.

Installing a purge valve from AFP is a potential solution to the problem and my airplane is already plumbed with a full return fuel system so the plumbing changes would be pretty easy. I might also benefit from other aspects of adding the purge valve, like hot starts etc. But, before shelling out the cash for the valve and cable and the work involved etc. I wonder if there are other solutions to consider? Has anyone had this problem and solved it another way?

Anyone have a purge valve laying around they would like to sell?

Ideas and experiences with this situation would be appreciated.

Randall in Sedona

[flyinga]

This is what the sniffle valve is supposed to do; drain the intake after shutdown. Mine leaves a small spot on shutdown occasionally. At least you know it's working.

[Bavafa]

Mine does exactly the same thing, including the oil mixed with the fuel. I have been trying to understand where is this oil coming from, but it has been doing it since the day one and nothing has changed since.

[MarkW]

I see some pilots push the red knob back in after shutdown. Some say it is safer so they don't hit it while getting in and out of the plane.
The red knob is also known as a ico. It shuts off all fuel going to the servo/spider and therefore the intake tubes. I have had many days after flying that I still have fuel pressure due to this being shut off. This is also a safety issue. If the engine has no fuel there can be no accidental start even if you have a broken mag wire.
If you push the red knob back in after shutdown all the remaining pressure in the system ends up with fuel in the sump therefore draining out your sniffle.

[Randy]

Thanks for the replies. It is good to know I am not the only one with this going on but I want to fix it. Mine is apparently a little more pronounced than most as I see a good 6" dia. circle on the floor after shut down. I have tried various shut down methods and the situation stays the same.

It reminds me of the old Harley Davidson motorcycles before they got there quality act together, I would see them park and pull out a drip pan with kitty litter in in to catch the oil

Randall in Sedona

[rswalden]

Originally Posted by flyinga

This is what the sniffle valve is supposed to do; drain the intake after shutdown. Mine leaves a small spot on shutdown occasionally. At least you know it's working.

Normal to have a drip or two after flight. I attach a small clip with a folded paper towel to the drain tube exit. The clip has a "Remove Before Flight" red ribbon hanging from it. Keeps the hangar floor clean.

[David-aviator]

Originally Posted by Randy

Thanks for the replies. It is good to know I am not the only one with this going on but I want to fix it. Mine is apparently a little more pronounced than most as I see a good 6" dia. circle on the floor after shut down. I have tried various shut down methods and the situation stays the same.

It reminds me of the old Harley Davidson motorcycles before they got there quality act together, I would see them park and pull out a drip pan with kitty litter in in to catch the oil

Randall in Sedona

If you had the AFP purge valve there would be no need for the sniffle valve, it does not leak.

[Steve Ashby]

I am in the engine installation mode, puting an IO-360 (180 hp) in my 8A. The FWF kit did not include a sniffle valve. Do I really need one?

Thanks!

[DanH]

Originally Posted by Steve Ashby

I am in the engine installation mode, putting an IO-360 (180 hp) in my 8A. The FWF kit did not include a sniffle valve. Do I really need one?

It depends. Is it likely that the manifold can collect a pool of fuel, and/or oil, or even rainwater?

As noted, a Bendix type fuel servo isn't supposed to leak much at ICO, but some do, and that can push fuel out through the nozzles in a stopped engine. An AFP purge valve returns leakage to the non-pressurized fuel system, so not much escapes through the nozzles.

Oil is an interesting question, as quantity may change over time...the source is the intake valve guide. There's no way it will pool enough oil to be a problem during one shutdown, but can it build, as liquid or long term sludge? I dunno.

There have been reported cases of rainwater entering down through an airbox/filter and pooling in the manifold. Not a problem if you're the guy who always parks with intake plugs, or uses an airbox with a good drain.

Manifold design can be a factor. The horizontal intake tuned Lycoming has a fairly large bottom plenum, so a fair amount of fuel could be present without reaching the level of an intake tube. A Superior "cold air" intake has almost no plenum volume, so anything collected in there is going to get snorted up an intake tube early in the starting process. An ECI has some volume, but I don't know what they look like inside. The new Ace looks like it could collect a quart on each side, and is designed with two sniffle valves.

Your call Steve; it's experimental. I run an AFP FM200, shut down with a purge valve, avoid the flood-to-hot-start proceedure, have a Lyc manifold, the ram-style intake doesn't collect much rain, and the airbox has a drain anyway. The sniffle valve failed a floatation test three years ago....

That said, if you're not confident, install one.

[BillL]

Originally Posted by DanH

<snip> The sniffle valve failed a floatation test three years ago....

So, you dropped it in a glass of water and it did not float? Or is there some more technical test?