Sniffle valve dribbles

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

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.

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.

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.

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

flyinga said:

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.

Click to expand...

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.

Randy said:

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

Click to expand...

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

Is a sniffle valve necessary?

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!

Steve Ashby said:

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?

Click to expand...

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.

float test?

DanH said:

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

Click to expand...

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

BillL said:

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

Click to expand...

I maintain a full time floatation test facility next to the shop. It is not very technical

Randy said:

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. <snip>

Randall in Sedona

Click to expand...

Randall, does it look like this? 6" rule in the second pic for ref:




Today's shutdown dribble with yesterday's...I left yesterday's spot just to show you what I see on each shutdown. No oil, just fuel?and it likes to wait till just after I push the plane back into the hangar?just to give me something to clean up! Never thought of it as an engine issue in need of correction though, just normal ops. Wiped up after the photo, so now I have to guess where to push back to next time! FWIW, IO-540 with Bendix servo, 90 deg elbow to an updraft sump. Sniffle valve is on the low point of the elbow.

Not sure what the fox would be short of removing the valve, but its nice that your being considerate of those you visit?last time I went to Rosie's place, I parked on the taxiway so he wouldn't have to chase me with a drip pan!

DanH said:

I maintain a full time floatation test facility next to the shop. It is not very technical

Click to expand...

Now that's funny raht thar?good thing I don't have one of those?there'd be a lot of twisted metal on the bottom, and fiberglass epic fails floating on top!

Cheers,
Bob

Bob,

Thanks for the photo. Yes, my "spots" look just like that only a bit larger.

For about $300 plus the control cable we can buy the purge valve from AFP and the problem gets solved, with some benefits such as easier hot starts etc.

Randall in Sedona

Not quite as simple as $300 plus cable. A good bit of plumbing to add too.

David-aviator said:

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

Click to expand...

Not necessarily. Much of the "fuel drip" after shut down is supposedly because the fuel that's leftover in the injector feed lines boils off and percolates into the intake from residual engine heat. Since the AFP purge valve is actually upstream of these lines, it won't have any effect on this.

MarkW said:

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.

Click to expand...

At my local airport, there is a whole group of Bonanza pilots that were taught by one person to push in the throttle and mixture vernier knobs after shut down so that they wouldn't get kicked when climbing out of the left seat. As stated above, this is a safety issue and is really stupid! I know of at least one pilot that knew this and tried (semi successfully) to reeducate these pilots about the dangers and lunacy of this technique!

Skylor
RV-8

Excessive leakage from the sniffle valve is a string indicator of a mixture control valve that is not sealing correctly.
The actual valve in a fuel servo is two circular plates with holes in them that rotate against each other. The actual seal is the metal to metal contact of the two plates (no seals). Even at idle cut-off there will be a small amount of leakage while the system is still under pressure after shut down. The normal leakage after shut down is expected to be below what the evaporation rate of teh fuel is, so you should ever see any excessive discharge. Sometimes the seal does not perform as well as expected and the pressure bleeds down at a much higher rate. That will result in liquid fuel flowing out of the sump drain.

I think I had that problem with an injected RV6A that I owned for a short time. In that case, the engine would not shut down cleanly with the mixture control and would stumble and shake etc. I finally adopted turning off the mags to avoid the stumbling.

On my new IO-375, pulling the mixture always stops the engine cleanly, no stumbles etc. The leaking from the sniffle valve will not start for about 5 to 10 minutes after shut down.

I assume from these symptoms that the servo ICO situation is OK.

I do however have a servo that is running too rich at full rich settings, giving me approximately 300F difference in EGT between full rich and peak, they tell me the spec is 200F spread.

Perhaps related?

Randall

Randy said:

I assume from these symptoms that the servo ICO situation is OK.

Click to expand...

Maybe.

A properly functioning mixture valve should be able to hold system pressure for a while (slow bleed down). I believe it is possible to have the valve function well enough to give good engine operation but still leak down too quickly.

One of the airplanes I maintain has had a drippy induction drain since new. The servo was sent out under warranty and it checked out ok but it still has the problem. If the engine is shut down by turning the fuel selector to off it doesn't have a single drip. Any other process (including the high idle for 30 seconds before ICO) and it will drip for hours.

DanH said:

I maintain a full time floatation test facility next to the shop. It is not very technical

Click to expand...

Nice!
And a convenient fire hydrant for keeping it topped off......

flyinga said:

Not quite as simple as $300 plus cable. A good bit of plumbing to add too.

Click to expand...

Or...

That's funny.. I went looking for my drip pan in the hangar and found it OK, but, it has two Subaru motors siting on it...

I am still looking for a string indicator. Even Spruce is out of stock... I think.

Randy said:

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

Click to expand...

Harley Davidson used a drip system to keep the primary and drive chains oiled. They had their quality act together pretty well, people just didn't understand it. You could turn the chain oiler off, but then you had to manually oil the chain.

-Marc