Woohoo! Got the Northill working.

[elmer fudd]

I've got it all sealed up and breathing, using my original diaphragm idea of 1/32" silicone sheeting sandwiched between two modified CD's with a SeaQuest exhaust valve fitted to the center.

Cracking pressure is somewhat high at about 2.5", but I think a little tuning and a redesigned diaphragm will correct that. For now, I think it's functional and I plan on taking it out diving tomorrow.

 

[herman]

Blasted vintage diving virus is a pain ain't it?
I got it from an old reg someone gave me....the %^##!!, now I have a couple of dozen regs and a machine shop set up to build the parts I can't get.

 

[elmer fudd]

I dunno, I think getting into vintage diving has pretty much shattered any ideas I might have had about scuba gear being too complex for the average diver to understand or work on.

After rebuilding 3 doublehoses and a few single hoses, fabricating parts, etc..., I don't think I'm going to feel the need to get any of my regulators serviced at a shop anymore. I've been studying regulator designs for the past few months now and it's been quite a learning experience.

It would still be nice to get into a factory regulator service class sometime though and maybe find a reasonably priced source of SP parts. There's something wrong when I can get new parts kits for obsolete regulators for about half the price of rebuild kits for modern regs.

 

[elmer fudd]

Well, it appears I only have it kind of working. I did a very short dive with it today, for about 5 minutes and to 10 feet before I had to abort and surface.

In the water, the reg wanted to free flow for some reason. I didn't abort the dive because of this though, as the air wasn't flowing that bad. It did make for very easy breathing though.

After about 5 minutes, I started to get some water in the mouthpiece. At first, I just checked the surface/dive mechanism to make sure I hadn't rotated it accidentally, but when it was clear that I hadn't, I decided to surface.

Looks like I have some more tuning and tweaking to do.

 

[Double Diver]

Well, it appears I only have it kind of working. I did a very short dive with it today, for about 5 minutes and to 10 feet before I had to abort and surface.

In the water, the reg wanted to free flow for some reason. I didn't abort the dive because of this though, as the air wasn't flowing that bad. It did make for very easy breathing though.

After about 5 minutes, I started to get some water in the mouthpiece. At first, I just checked the surface/dive mechanism to make sure I hadn't rotated it accidentally, but when it was clear that I hadn't, I decided to surface.

Looks like I have some more tuning and tweaking to do.

The factory spec for lever height is 1/6" below the top of the can. This is of course this is with the original diaphragm. So your levers will need to be tweaked to your new diaphragm accordingly. Did you rebuild the non-return valves? If not this is part of your cracking and water ingress problem.

 

[elmer fudd]

It's got no non-return valves in it. It didn't come with any. I'm not sure if that's because they're missing or if it was an early model that just didn't have them.

My theory on what happened is that I got it adjusted badly to begin with and things just kind of cascaded from there. I was doing the original trial and error with an 1800 psi tank that got partially discharged over about a two week period as I tinkered with things. When I finally thought I had things ready to go, I set the levers as high as I could manage without a free flow, to decrease the cracking pressure.

Unfortunately, I hadn't taken into account the higher tank pressure on a fresh lp72 pushing that floating valve up higher and depressing those levers against the diaphragm. I'm pretty sure that's the explanation for the free flow.

As far as the water in the mouthpiece, I'm still not quite sure. I'm mostly suspicious of the mouthpiece though. It just seems to me that the other vectors for water to get in would have been minimized by my position in the water and the fact that the reg was free flowing.

On my next dive I'll use a hose assembly from an Aqualung just to help rule things out.

I'm going to try a new diaphragm design as well. Since this is a flat diaphragm, that means that the material has to actually stretch to activate the levers. On an accordion type diaphragm the baggy material or the little roll of rubber near the edge allows movement without much actual stretching.

I followed pretty close to the original dimensions, so between the solid portion of the diaphragm and the cans there is a ring of silicone rubber perhaps only a quarter inch wide. That's not much stretchable material and I think it's raising my cracking pressure considerably.

On my new diaphragm, I plan on putting a plate on the bottom that will contact the levers and using a smaller diameter plate on top with the silicone sandwiched between the two. This should allow me to extend the stretchable portion of the diaphragm considerably and should allow for easier breathing.

 

[Double Diver]

Well I think you have a very good grasp of the situation with the exception of one point. The floating valve which is unique to Northhill does not push the levers up as the tank presser rises. In point of fact it lowers them to compensate for the higher presser by increasing the tension on the HP spring. As this is a down stream HP seat it would definitely free flow at higher pressers, but since it is compensated for by the use of a floating HP seat I believe your problem is the lack of flexibility in the diaphragm material. PM me if you would like to talk about this further.