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Post by vance on Jun 6, 2019 17:46:50 GMT -8
Finding a tabbed diaphragm in good condition these days is tough and no one appears to be making them currently. It is (was) awesome that replacement parts for the DA were being made. I hope that it isn't a marketing ploy by the maker/seller to discourage restoring these old regs to stock by not providing this option, thereby making it necessary to replace the stock second stage with a redesigned second stage (that they produce and sell) that uses the single stage type diaphragm. I don't want to be cynical, but there are other hints that DA parts are not being made any longer (except for upgraded, non-stock regs) and those who are interested in restoration, not modification, are SOL. I understand that the production of restoration parts is probably expensive, the market is small, and it might not be feasible to continue supplying parts. Oh well. End of an era. I guess we're lucky to have an alternative at all.
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Post by scubalawyer on Jun 7, 2019 20:09:38 GMT -8
Good thing I have a few extra from old DA Aquamaster teardowns. The next reg I restore that needs a tabbed diaphragm I'll just use a new single stage silicone diaphragm and attach the old tab plate as I've done before. M
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Post by Michel on Jun 11, 2019 5:50:14 GMT -8
That's a great idea if your originals are torn or really bad. I have rarely seen any that were beyond serviceable except for being a little stiff. I think VDH was making tabbed silicone ones at one time but may have stopped for reasons to concentrate on their new improved horseshoe set up and using their single stage(Mistral type)silicone diaphragms. IMHO the silicone diaphragms don't really make a huge difference to me except for flexibility and longevity so I don't worry about it. Michel.
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Post by Fibonacci on Jun 11, 2019 14:01:37 GMT -8
The biggest problem I can see with the VDH diaphragms is the total lack of standoff flanges, bosses or ribs.
On my Nemrod Snark DH I did a quick test: Connected up the unrestored Snark III to a couple of tanks just to see how it may go... the reg seemed nearly new very few dives... all rubber parts supple. NO leaks at all! Breathed very well.
Checking on the Magnehelic:
OEM Nemrod diaphragm, hoses, mouthpiece. Tank pressure 115 BAR (1668 psi) 1.1"
As above with VDH silicone diaphragm 0.9" improvement of only 0.2"
OEM Nemrod diaphragm, VDH Kraken hoses and DSV. Tank pressure 115 BAR (1668 psi) 1.1"
OEM Nemrod diaphragm, VDH Kraken hoses and DSV. Tank pressure 215 BAR (3118 psi) 0.8"
The Nemrod Snark OEM diaphragm has radial 'anti-sticktion' ribs, a central standoff boss AND two domed metal pillars inside the can... no way it is going to 'suction cup' against the exhaust valve!
From what I can see on my RAM OEM diaphragm, it appears the stainless plate was co-moulded with the rubber, not glued. There is tell-tale flash and manual trimming marks. These would be tricky to replicate in low volume, but not impossible.
Wonder what the market for accurate 'restoration quality' USD diaphragms would be?
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Post by Deleted on Jun 12, 2019 8:18:30 GMT -8
It is impossible to second guess why something was done in the past by anyone unless it was documented.
That said; Having not seen nor heard of any documentation of why the RAM diaphragms have a tab, I can only surmise that, given USD was still a small company with minimal profit margins and trying to cut costs in every way, then comes along some poor design engineer who makes a mistake mathematically and had the stamping molds for the 2nd stage lever made with the lever length and height too short. Upon discovering this, USD opted to just alter the stamp molds for the diaphragm disc by establishing a second stamping process that cut the tabs and bent them vs the expense of having a new stamping mold made for the lever. Saving money. IE: a work around.......common in design and pre-production.....achieves the same thing with less cost....except the poor design engineer either was demoted or fired.....or most likely promoted due to his or her solving the problem created by their mistake..........to me it is interesting when one gets into the history of why something was done vs our ever loving 20/20 hind sight on how it should have been.....
A new stamping tool could be made today, reversed engineered. I would estimate between $500 and $3000, depending on who you have do the work. However, that cost most likely will never be recovered. It would be cheaper to have a new mold made for the diaphragm's and just transfer the old tabbed disc's like Scubalawyer stated he does.
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Post by SeaRat on Jun 12, 2019 12:15:51 GMT -8
I am going to chime in here, as to understand the reason of the tabs on the USD LP diaphragm, you need to know the underlying technology. In the 1940s and early 1950s, metal work was in its infancy. Surfaces could not be polished like today in a cost-effective manner. So the original engineer, probably Emilie Gagnan, came up with the metal tab on the diaphragm interfacing with a convex surface of the LP horseshoe lever. This means that the thin convex edge of the tab impacts the convex surface of the Horseshoe lever. There is minimal surface area touching both surfaces, which decreases the resistance (friction) as the two surfaces move against each other. In addition, as the diaphragm moves down upon the lever's convex surface, the two meeting points move slightly as a tire would move, Therefore, even in the first DA Aqualung, resistance to movement is minimized.
In contrast, the polished surfaces of the compound lever system in the DW Mistral (and its predecessors), slide against each other, and against the smooth diaphragm plate. Here, the resistances are compounded.
Later, the single hose regulators incorporated the Teflon-coated lever to minimize this resistance. Modern double hose regulators are using this latter concept, and see no need for the flanges used by USD. This simplifies repair (the technician doesn't have to closely align the tabs with the horseshoe lever), and comes closer to the resistances of the original tab/horseshoe lever system without having to machine the convex surface for the horseshoe.
Also, since USD used a duckbill exclusively as the exhaust valve (which I still feel is superior to the mushroom valve), there was no need for any anti-suction ridges on the outside of the LP diaphragm.
John
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Post by snark3 on Jun 12, 2019 12:43:18 GMT -8
I just did the opposite of reglueing. I have a DAAM that looks like it ended up on the wrong side of a car tires (like under them) the cans are severely bent and the diaphragm was severely distorted. I took the metal plate off so I can cut it down and hopefully make an exhaust valve for a Northill. This one looked like the rubber had actually molded into the holes in the metal where the tabs were cut from.
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Post by Fibonacci on Jun 13, 2019 21:35:01 GMT -8
My RAM diaphragm is still quite supple and in good condition, well bonded to the tabbed plate... so I don't want to disturb it. Would anyone be able to accurately measure the plate diameter using a vernier (in MM) please?
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Post by vance on Jun 14, 2019 8:03:25 GMT -8
My RAM diaphragm is still quite supple and in good condition, well bonded to the tabbed plate... so I don't want to disturb it. Would anyone be able to accurately measure the plate diameter using a vernier (in MM) please? The plate in my single stage diaphragm (the only USD diaphragm I have not inside a regulator) is very close to 82mm. It should be the same diameter plate as the tabbed one. Has anyone tried the super glue I suggested?
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