Whaddaya know about Northill Air Lungs?

[elmer fudd]

I believe most diaphragms today are made out of silicone rubber. The original diaphragm is a compound design. It has an exhaust valve right in the center of the demand diaphragm. It also uses 2 diaphragms that vary in thickness and contours and the outer one has eight tabs sticking out to fit the screw tabs.

I suspect that trying to make an exact copy of the original would require much more time and money than I'm willing to spend. The basic concept however isn't that tough. I basically just need a diaphragm of the correct size with an exhaust valve in the middle.

That's why I'm thinking a sheet of silicone attached to a plate with a modern style exhaust valve attached to the center of the plate. That's something I can do fairly easily. I tested the concept by using the original diaphragm plate and the .025" sheet latex from my HydroGlove waist band. I just laid the latex over the plate and then held the two cans together creating a seal and inhaled to test it and it seemed to work fine.

The one concern I had was hard breathing/high cracking pressure. If you look at most any diaphragm, you'll notice a billows type feature near the edge. That's there to allow more travel with less resistance. Obviously my homemade diaphragm won't have that, and I hope this will lead to only slightly higher breathing resistance.

 

[knowone]

Are you talking about diaphragms or speakers.

The black stuff is almost paper thin, very fine fabric reinforced epdm.
Helmut the seal guy had the right size cutters, out of a flat sheet and
a hundred O rings or so for twenty bucks. He happens to be a diver.

The internal rubber sealing ring is original and although difficult to gauge is
thicker than the epdm.
The cans sealing ring, thick 2mm silicone I cut using fruit tins as templates.

This stuff is very strong and yet you can cut it, seal it, glue it, make tabs.

This setup uses no adhesives for sealing, only compression.

It is does not stretch and is very laterally flexible therefore
offering no resistance to ambient or vacum when breathing.

Very good.

 

[elmer fudd]

That looks like a great setup. If I were to build something similar, add some holes to the center of the plate and then put an exhaust valve in the center it would work.

I picked up the silicone sheeting today, but I'll check out the fabric EDPM too as the silicone seems pretty thick.

 

[knowone]

I omitted (manufacturing diaphragm material used for hundreds of non diving related)

You could look up DIA.COM, or WarwickMills, a couple of USA mobs as an indicator.


This thing is an old locally made single hose.

It is silicone on an aluminium frame and breathes exceptionally well.

Do you have any photos of your crumbling crusty things.

 

[Double Diver]

Yes, at one time I had one of these damed things. They were the noisest regulator I ever saw. They were eqipped with a shut off at the mouthpiece. The unit exhausted under and through the diaphram, a dangerous arrangement. If you lost the mouthpiece without shutting it off the entire system would flood! Then lifting the hoses above one's head would not stsrt the air flowing. The only way to get air flowing was to pinch the hose at the mouthpiece and extend it upward. Sometimes this would start the air flowing. Then you would get about half air and half water. Start rolling and blowing and maybe you gould clear it. Aside from that it was well built from brass castings. Only dive it in a swimming pool.

Ben did yours have the non-return valves installed? It was a later upgrade as I heard it.
And the guy I heard it from bought two of them in 1955 and he and his wife dove them for years. I have both of them now and have rebuilt one. I tried it with and with out valves in the pool and you are right! But with them in place it works well.
Also he gave me his original copy of the instruction/parts/overhaul manual and the exhaust NR valve must be located next to the exhaust port not the mouthpiece as is the norm on DH regs.

 

[Double Diver]

I'm lucky I have 3 Northhills with good diaphragms, but there's nothing like silicon to lower cracking presser. So I was thinking about using speaker rebuild kits. There are a number of them that use very thin EPDM or silicon and the trick would be finding the right diameter for the primary diaphragm, the exhaust could be any silicon material thick enough to not get pushed through the exhaust holes.

 

[elmer fudd]

Double Diver,

Mine doesn't appear to have the non return valves. I'm not sure whether it's an earlier model or they're just missing. My understanding is that the exhaust NR has to have a hole in it because of the way the diaphragm is activated.

Do you have any information on how that works? How big the hole is? Any effect on work of breathing?

My guess has been that the hole is located in the center and just the fact that gravity will tend to keep water low means that water will tend to be below the level of the hole.

 

[knowone]

Did you manage to get a hold of those manuals, elmer fudd?

 

[elmer fudd]

I have a manual on order. It's supposed to be a compendium of DH service manuals, including the Northill manual.

 

[Double Diver]

Double Diver,

Mine doesn't appear to have the non return valves. I'm not sure whether it's an earlier model or they're just missing. My understanding is that the exhaust NR has to have a hole in it because of the way the diaphragm is activated.

Do you have any information on how that works? How big the hole is? Any effect on work of breathing?

My guess has been that the hole is located in the center and just the fact that gravity will tend to keep water low means that water will tend to be below the level of the hole.

Mr. Fudd,
These specs are per an original operation and repair manual which includes the supplement on the NRVs.
The NRVs are located in the hoses. They are pushed in to the hose about 2 or 3 ribs.
The intake is next to the mouthpiece and the exhaust is located next to the can. The you are right about the exhaust having a hole in it, the 1/4" hole is off-center. As fare as WOB it does not effect it in any big way.