Homemade restrictor fitting

RVG8tor · #1 05-19-2011, 01:18 PM

I need a restrictor fitting for the manifold pressure line, only 2 supplied with the FWF kit (one each for Oil and Fuel) Van's sells them for $19.50 (VA128) but I read how some guys make them on this forum. I don't own a #60 bit the closest I can some up with is 1/16". So is there anything magical about the .040 hole in the restrictor Van's sells.

The restrictor is there to prevent a catastrophic leak of air if one of the lines connected to it break, so a 1/16" hole would allow a slightly bigger leak over a .040 hole but should serve the same purpose yes?

I have the fitting threaded and will JB weld the bolt into the fitting then cut off the end.

Cheers

SteinAir · #2 05-19-2011, 01:42 PM

Quote:

Originally Posted by RVG8tor

I need a restrictor fitting for the manifold pressure line, only 2 supplied with the FWF kit (one each for Oil and Fuel) Van's sells them for $19.50 (VA128) but I read how some guys make them on this forum. I don't own a #60 bit the closest I can some up with is 1/16". So is there anything magical about the .040 hole in the restrictor Van's sells.

The restrictor is there to prevent a catastrophic leak of air if one of the lines connected to it break, so a 1/16" hole would allow a slightly bigger leak over a .040 hole but should serve the same purpose yes?

I have the fitting threaded and will JB weld the bolt into the fitting then cut off the end.

Cheers

There are many ways to go about building your own restrictor fitting and they all work pretty well. In the MP, it's no so much for an air leak (don't think that an open MP line would be anywhere near catastrophic), but to settle down the sensetive MP instruments. Some of them are so sensetive they'll register each intake stroke and it gets quite annoying without that restrictor in there. The FP and OP are much more critical from a leak standpoint than the MP is, but the MP is much more sensetive to variation in pressure readings (my point is the orifice size for the MP isn't a critical thing other than to smooth out pulses, not necessarily for leaks).

I say do what you can and go fly. If you MP instrument isn't too jumpy then you'll be golden.

Just my 2 cents as usual,

Stein

dpansier · #3 05-19-2011, 01:48 PM

Drilling a very small hole can be difficult without the proper tools.
Wire feed welders use a very small tip .020", .025" and up, this tip could be used to make a restrictor.
If you know a welder you may be able to accrue one as they usually toss them out after a short use.

AirbusPilot · #4 05-19-2011, 01:48 PM

I used a hypodermic needle welded inside a brass tube. that is air models turbines techniques

TS Flightlines · #5 05-19-2011, 02:02 PM

Use a piece of 1/8 tubing, flare one end (so it fits snug in the fitting), then you can JB weld or braze it in place. Cut off the excess to make a nice end.
Takes a couple of minutes.
Tom

alpinelakespilot2000 · #6 05-19-2011, 02:05 PM

Mike,

Not homemade, but here's a cheap version from Wicks.

http://www.wicksaircraft.com/catalog...767/index.html

RVG8tor · #7 05-19-2011, 03:51 PM

I am making mine like I read from someone on this site. I tapped the inside of the fitting to 10-32. Then drilled the hole (1/16" diameter) down the center of a #10 bolt. With a litle JB weld I threaded the bolt into the fitting. When it sets up after 24hrs I will use a cutoff wheel to cut the bolt off at the end of the fitting.

I noted that Van's and other restricters used a .040 hole size. I do not have a #60 drill so I made a larger hole with the 1/16" bit I had on hand. I will just try this for my manifold pressure line, if it fluctuates too much then I will know there is something to the hole size.

Cheers