What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Sniffle valve.... yes or no?

sniffle valve yes or no?

  • Yes must have a sniffle valve

    Votes: 42 66.7%
  • sniffle valve is not really needed

    Votes: 21 33.3%

  • Total voters
    63

hydroguy2

Well Known Member
I've got a IO-360, AFP injection and Superior forward sump. What's the verdict on sniffle valves? needed or not?
 
Yep

I just went through the education process on sniffle valves. After a few chuckles regarding the nature of my inquires the verdict seemed to be that vertical sumps don't need one but horizontal sumps do. Has to do with excess fuel collecting in the sump and being a hazard for backfires etc. The vertical sumps allow the fuel to drain out the throttle servo, but the horizontal ones collect it in back of the sump which is where they put the drain hole for the sniffle valve.
Hope this helps.
 
NOPE

Sorry to contradict Grandy, but it is not needed IF you installed the cutoff valve from AFP. If you do not have the cutoff valve, then yes, you need the sniffle. The AFP system does not fully cut off the fuel flow with the throttle fully retarded. The cutoff valve keeps the fuel in the spider from draining down into the cylinders and into the intake. I don't believe it matters which intake you have because the Rockets use a vertical sump and the fuel pools in the intake elbow where it can cause a fire if the engine backfires. I have no knowledge of horizontal sump engines.

Give Ron at AFP a call. He will be happy to answer any question you may have.
 
Last edited:
NO

You really don't need one either way, purge valve or not. Unless you've got one of those plastic sumps, then... are there still some out there that haven't blown up yet? My -6 with an IO-360-A3B6D with Bendix injection has been happily without for 320 hours (this engine's been without for 2320 hours) and I haven't missed it yet. No clue why so many folks are so adamant that you MUST have one. In fact, see parts catalog below, MOST of the injected horizontal sump engines DID NOT come with one originally.

Of course, if you're superstitious, then by all means install one...

sniffle%20valve%20PC.jpg

sniffle%20valve%20PC2.jpg
 
You have a Bendix injection, not a AFP. They don't work the same and they are not interchangable. I'm not superstitious, I just called AFP and spoke to someone who knows the differences.

The other option is to leave the sniffle valve off and see if pooling fuel is a problem on your install. You can always install the sniffle valve later.
 
Last edited:
I sure like my sniffle valve

on hot starts (superior io360 180hp, horizontal cold air sump). Sniffle valve makes it hard to really flood the engine by draining excess fuel. A "flooded" hot start process works great every time.

Throttle & Mix in.
boost pump for a couple seconds
Mix out and crank till it catches.
Mix in and Throttle back to idle
boost pump on as req'd to keep running.

The sniffle valve makes this easy cause no overly large quantity of fuel can remain in the sump.

THE BAD THING about the sniffle valve is the pool of fuel & oil on the hangar floor after every flight. Plan on running tubing from the sniffle valve aft to drain it at a convenient spot.
 
I have a horizontal sump with a sniffle valve and experience the oil/fuel drips. What I don't understand is where the oil part of the drainage is coming from...seepage from the intake valve guides?
 
Intake guides

are the only source I can think of for the oil that ends up on the floor. Without a sniffle valve, this oil would eventually end up going back through the engine. Probably not a bad thing (top end oil). It's a little bit of a mess but I like the fact that I don't dump lots of extra fuel through the engine on a hot start...
 
I did not install a sniffle valve when I built my RV7 and was lucky I did not ruin my engine. I was in St Louis one time and had to delay my takeoff due to very heavy blowing rain of several hours duration. When I went to start my engine, the prop rotated about half a turn and stopped. I got out and tried to pull it by hand but it would not turn. I took the cowling off and could not see anything wrong. Tried starter again with same result. I didn't know what else to try so I removed a plug from each cylinder and imagine my surprise when water came out of one cylinder. The engine was hydrolocked. I was lucky cause if one cylinder had fired up, I probably would have bent a connecting rod or worse. Anyway, I removed the plug that I had installed in the sniffle valve hole, drained a bunch or water out, pulled the prop through several times to get water out of the cylinders, started it up and all was well.

I have the Vans vertical induction on my IO360 that goes to the front of the baffle and had never heard of a sniffle valve till I called Vans and informed them of what happened. I bought a sniffle valve and also suggested that they put something an the RVator but they never did.
 
I install a sniffle valve.

The ECI Horizontial induction had a red plastic plug in the location of the sniffle valve when my engine arrived. I could either plug it or install the valve. I choise to install the valve. ;)
 
Precautionary components

Sniffle valves (like fuel filters and carb heat systems) are precautionary components in Firewall Forward systems and not absolutley required or necessary for the engine to operate. These systems are designed to prevent certain failure modes in the event that some out-of-sequence or non-standard event occurs. That event could be the result of fuel drainback into the sump or water ingestion from a few days parked on a rain soaked ramp. Both could ruin your engine and your day. Just think of it as another insurance policy.

A sniffle valve (Lyc P/N LW-75444) is only used on Horizontally Inducted, Fuel Injected engines on RV's, in which the Injection Servo is mounted to the forward face of the sump. A Vertical Inducted engines does not require one.
 
Here's a excerpt from an email I received from AFP:

With the correct use of the purge valve for starting and stopping the engine there should be no fuel getting into the sump. However in the event that proper procedure is not used, a manifold drain (sniffle valve) might be a good piece of insurance.

So seems the safest thing to do is put one on, but not absolutely necessary. I have elected to follow procedure, hangar my plane, don't fly in the rain and NOT install the valve. YMMV and I may grenade my motor.;)
 
Test that sniffle

Just make sure you test the sniffle valve. The first one I got from Superior leaked air when it was supposed to be closed. They said they'd never seen one do that before. Yah, right.

One might get erratic running if this thing decided to leak just occasionally...

Otherwise, might not be that much diff...

Anyhow, never had a problem with my trike but understand quite a few TD's did.
 
Right-Angle Sniffle Valve

Joe posted a part no. for a sniffle valve. I bought one of these from Van's.
However, with my TMX-IO-360-M1B this straight sniffle valve conflicted with my Vetterman's cross-over exhaust.

I solved it with a Piper right-angle sniffle valve - Piper P/No is 492-091.

Search VAF on this P/No and you'll see it quoted by Mahlon at Mattituck.

It's a shame that Van's don't offer the right-angle part.
 
90 degree Manifold Drain

Or you can order P/N 1090138 Manifold Drain ($21.00) and P/N AH-3400X2 90 degree pipe fitting ($1.50). And there you have it all for $22.50.

Don
 
Similar to a previous post I had the "hydrolock" problem on my new Lyc with the Silverhawk injection. So much fuel accumulated during the "washout" process suggested by Lycoming to purge the preservative oil that the engine locked up. Was also lucky that it did not start and bend something!

After draining the cylinders and trying again I finally took the plug out of the hole the sniffle valve goes in and almost a quart of fuel came out. After that drain it started normally but I didn't start it again until I had the sniffle valve in place.

In my view the horizontal injection with the Silverhawk requires the sniffle valve but it was never so stated in any of the instructions and a sniffle valve is not part of the FWF kit from Vans.

BTW, I bought the onewith the 90 deg bend on the outlet that is used on the Piper Twin Comanche and it was easier to install. The one Vans sells is sort of blocked by the heat shield and Vetterman exhaust.
 
The reason so many engines DON'T have it from Lycoming is because usually the airframe manufacturer spec'd and added their own afterward. You pretty much want to have one to protect your $30+K engine.
 
unsure

Sorry to rehash this old thread but I have taken position of my IO 360 AIA with bendix FI... I am about to order the FWF kit (minus a few items)....I am trying to figure out if my engine already has or needs a sniffle valve. Where would it be located. sorry for my ignorance...

photo of the engine prior to tear down and clean up..

Eng3.jpg
 
It's on the bottom of the intake sump, looks like an oil drain plug but it's in the intake sump not the oil sump.
 
Just to throw some thoughts out there for debate.

Forget the water argument for a minute. The valves only purpose is to drain excess fuel that pools in the intake sump.

How effective is that on a taildragger? Just looking at mine sitting here and there is room for a significant amount of fuel to pool at the rear of the manifold.
So, for a taildragger is a sniffle valve really doing anything?

If the valve is installed, by it's very design, will vent any pressure in the manifold that is in excess of ambient cowl air pressure, degrading manifold pressure recovery when the lower cowl pressure is ambient or slightly below.

Bringing back the water argument, a manual valve would seem to sufice. Wouldn't a manual or electric actuated valve be just as useful?
 
Last edited:
I have a horizontal sump with a sniffle valve and experience the oil/fuel drips. What I don't understand is where the oil part of the drainage is coming from...seepage from the intake valve guides?

Mine has been doing it since day one and still doing it after 300+ hours. A number of calls to Lycoming gave me unsatisfactory answers but all consensus are that is from the guides and nothing to worry about. It is only a few drops at most.
 
snifl valve

I do not use a valve. IO-360 horz. induct. AFP injection/purge valve. I use the port to get MP, This gives a average of all cyls. 850hrs. on engine no problems.
 
....I am trying to figure out if my engine already has or needs a sniffle valve. Where would it be located...

Here you go Ryan....AFP sniffle, the blue fitting. Plumb a line to a point just outside the cowl cooling air outlet, or anywhere else allowing liquid to drip to the ground.

10pozty.jpg


If the valve is installed, by it's very design, will vent any pressure in the manifold that is in excess of ambient cowl air pressure, degrading manifold pressure recovery when the lower cowl pressure is ambient or slightly below.

Interesting point. As you say, it is a matter of relative pressures. Plumbing the sniffle to the cowl exit should cause it to open and flow air down the drain tube in the special case of excellent dynamic pressure recovery and high IAS. For a SARL guy at 200 knots and 2500 ft, theory says sump pressure would be higher than ambient by 0.8 to 0.85 psi, given the pressure drops reported for better filtered and unfiltered intakes. However, given a large enough intake opening, would it result in any measurable pressure loss to the engine? The supply is unlimited while the leak is limited to flow thorugh a constricted -4 fitting.

Hmmmm...I have a few small Parker solenoid valves....
 
Back
Top