REFLECTOR: Fuel resistant adhesive, homemade sniffle valve - (2nd attempt with images)

[Dave Philipsen]

Here are a couple of photos of my homemade sniffle valve.

             
      
The photo on the left shows it completely assembled and the one on the 
right shows it taken apart.  The part on top is a 1/8"  brass pipe 
nipple.  The next part is a 3/8" x 1/8" male pipe to FIP bushing.  The 
next is a part of a 1/4" x 1-1/2" nylon hex-head machine screw.  And the 
last is a 3/8" x 3/8" I.D. barb to FIP adapter.  All of the parts came 
from Lowe's.  The three brass parts are made by Watts and the part 
numbers are A-715, A-776, and A-298.  The nylon screw is made by Crown 
Bolt Inc.

I am going to install two of these on my IO-360.  I have created a 
suction on the threaded side and it closes off pretty well with very 
little leakage.  I have also run water through it and it passes through 
at a fairly good flow.  There are two basic reasons why this works.  The 
first is that the 3/8" x 1/8" bushing has a nice flat surface on the 
bottom of it that acts as a seat for the nylon screw head.  The second 
is that the 3/8" x 3/8" barb has a beveled seat for the screw head to 
fall into when there's no suction.  The fact that it is beveled and the 
screw head is basically flat keeps it from sealing which allows fluid to 
pass through it.  As you can see, I cut off the screw head but left 
about three threads of the threaded portion.  That small threaded 
portion is kept in order to keep the screw head fairly centered and to 
prevent it from getting cocked off at an angle.  It fits nicely into the 
hole in the bushing.  If you leave too much of the threaded portion, it 
will start to impede the fluid flow that must flow past it (by 
gravity).  I also cut a slot crosswise across the threaded section to 
help allow more fluid to flow past it (used a Dremel tool with cutting 
disc).  In addition, I cut a slot across the hex head for the same 
reason.  The fact that the screw has a hex head and the barb is round 
prevents it from making a good seal on the bottom which allows the fluid 
to flow past it.

The bottom side of the hex head (same side as the threaded portion) must 
be as smooth as possible since it will seat against the 3/8" x 1/8" 
bushing.  If you look very closely, the nylon screw has some little 
ridges there probably from the mold used to make it.  Before I cut the 
major portion of the threads away, I chocked them in a drill and spun 
the screw using a little 100 grit sandpaper to smooth out the bottom 
surface of the hex head.  I also chocked the nipple with the bushing 
attached to it in a drill and smoothed off the flat area on the bushing 
using the same method in an attempt to make it as flat as possible.  I 
also chocked the screw in the drill after inserting it into the 
bushing.  I spun the screw and applied pressure against the bottom side 
of the screw head with the bushing.  In effect this "burnished" the 
nylon with the brass seat to help them seal better.

Care must also be taken when screwing the bushing into the barb.  You 
don't want it to tighten down too much else you will squeeze the screw 
head.  Enough space should be left so that the screw head will move 
maybe .030" or so up & down.  you can test it by sucking on the threaded 
end while allowing the barbed end to hang straight down.  You may even 
want to use some teflon tape on the threads to prevent it from going on 
as far.

I have a real Lycoming sniffle valve that I paid thirty bucks for (just 
the valve without a nipple on it!) and this homemade part appears to 
work in the same fashion.  You may have to do a little tweaking and 
someone may even have a suggestion to make it work even better.  The 
nice thing is that it cost me less than ten bucks and I can easily take 
it apart and change the valve if I need to in the future.  One other 
thing, it needs about 2-1/2 to 3 inches clearance under your sump.  Make 
sure that it will clear the cowling.

I'm open to any comments or criticisms on this.


> Dave,
>
> Could you be a bit more specific on what fittings you are using for the
> sniffle valve?  I need to come up with something for my IO-540.
>
> Keith Hallsten
>   

-- 
Dave Philipsen
Velocity STD-FG
N83DP





-- 
Dave Philipsen
Velocity STD-FG
N83DP


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