Question LP Diaphragm Production (For Older Poseidon and US Divers Regulators)

[Erik22]

Hey guys,

I have begun producing LP seats out of 1/16 EPDM and a 9/32 punch. I would like to now produce some LP Diaphragms as well.

I have had some success making the LP seats fit in the Poseidon Cyklon (don’t want to pay $20 a piece) but I haven’t found a good price for the 1189 diaphragms found in the Cyklon 300 reg and others.

After studying the material, it appears that the diaphragms are made of a fabric reinforced neoprene sheet.

I measured my used 1189 diaphragm and it is a hair over 36mm in diameter. Maybe that is because it has been in the reg for 30 years and has extruded slightly past 36mm. The thickness was also hard to gauge, but it was in the 2mm (80 thou) range.

I also compared a US Divers style LP diaphragm. It was made/procured from The Scuba Museum and is not the best quality. The thickness is 100 thou, which is thicker than the original. It is roughly 35mm in diameter.

Obviously, there are tolerances and these parts can be thicker or thinner and still function.

My idea is to use 1/16 material from McMaster Carr
SKU: 8698K71
punched out with 35 and 36mm punches

Erik

 

[Erik22]

This material was my second option
McMaster Carr
SKU: 2658T51

 

[Fibonacci]

Either of those materials would probably work... for a while.
You need to find Diaphragm Insert rubber sheet, which is specifically designed to flex repeatedly under load.
I usually use this, but there will no doubt be a US supplier of similar material.
Fibreglass reinforcement is the best for underwater use (Nylon is somewhat hygroscopic) , but very hard to find as Diaphragm specification.

Diaphragm Sealing | Oil Resistant | Nitrile Diaphragm

Reglin Nitrile Diaphragm is designed for use as a rubber sealing diaphragm, it is oil resistant and reinforced with a nylon fabric for high burst strength.

reglinrubber.com.au

 

[Erik22]

Thanks for the suggestion, Fibonacci. It appears that your material listed is similar to the EPDM Fibreglass reinforced material. Tensile strength for the Reglin Nitrile is 1800psi, 1500 for the EPDM. Durometer is 70 and 50. I might be able to make a suitable diaphragm out of this material. Of course I would love to beat the piss out of it while testing to see just what it can and cannot do and try to quantify that data in a suitable way.

In the mean time, I will look into securing some of the Reglin Nitrile.

Erik

 

[Bigbella]

I measured my used 1189 diaphragm and it is a hair over 36mm in diameter. Maybe that is because it has been in the reg for 30 years and has extruded slightly past 36mm. The thickness was also hard to gauge, but it was in the 2mm (80 thou) range.

I also compared a US Divers style LP diaphragm. It was made/procured from The Scuba Museum and is not the best quality. The thickness is 100 thou, which is thicker than the original. It is roughly 35mm in diameter.

Before any great expenditure on materials, I would procure an actual 3884 or 3886 service kit, now available over the counter, and measure a new diaphragm size, over any museum piece, since crap distorts, occasionally even shrinks with age.

My oldest diaphragm use record was a bit over eight years with an old Cyklon 300, which was flipped with each servicing and was eventually ragged around the edges.

Years ago (when spare parts were a huge issue and I was South of the Border), we experimented with cobbling together diaphragms for the 2980s, from a Mexican tire repair product, which came in a sheet sufficient for seven or eight strikes -- made of a damn tough rubber and fabric combination that closely resembled the original material.

The tolerances, for the diaphragm, to sit flat and remain airtight were awfully exacting; was far more difficult than it looked, and took quite a few attempts.

While it did finally work, it didn't last too long, perhaps due what @Fibonacci had mentioned about hydroscopic properties of the fabric (which hadn't ever occurred to me) within the diaphragms. After a few months of use, we began to experience incremental leaks and an odd black exudation from the rubber material itself . . .

 

[Erik22]

Before any great expenditure on materials, I would procure an actual 3884 or 3886 service kit, now available over the counter, and measure a new diaphragm size, over any museum piece, since crap distorts, occasionally even shrinks with age.

Silent Explorers Maple Grove Minnesot United States Online SCUBA

Silent Explorers, Brooklyn Park, Minnesota, United States, online sales vintage Aqua Lung Double Hose Regualtor parts, Poseidon Rebreathers Regulators, Professional CCR Regulator Service, Shearwater Dive Computers

www.silentexplorers.com

My oldest diaphragm use record was a bit over eight years with an old Cyklon 300; was flipped with each servicing and was eventually ragged around the edges.

Years ago (when spare parts were a huge issue), we experimented with cobbling together diaphragms for the 2980s, from a Mexican tire repair product, which came in a sheet sufficient for seven or eight strikes -- made of a damn tough rubber and fabric combination and closely resembled the original material.

The tolerances for the diaphragm to sit flat and remain airtight were awfully exacting. It took a few attempts.

While it did initially work, it didn't last too long, perhaps due what @Fibonacci had mentioned about hydroscopic properties of the fabric (which hadn't occurred to me) within the diaphragms. After a few months of use, we began to experience small leaks and an odd pitch-like exudation from the rubber material itself . . .

Bigbella,

I will be at my LDS tomorrow and have access to a 3884. I will also bring my callipers and measure the diaphragm.

I saw that the kits from Silent Explorers were available, but I didn’t like the price.

However, if you can get 8 years out of a diaphragm, that $40 really isn’t so bad. The seats and o rings are hella cheap too. I have a bunch from the Cyklon second stage rebuild.

Also, thank you again for sending me a spare Cyklon 300 pin. That was in back in 2021!

Erik

 

[Bigbella]

I saw that the kits from Silent Explorers were available, but I didn’t like the price.

However, if you can get 8 years out of a diaphragm, that $40 really isn’t so bad. The seats and o rings are hella cheap too. I have a bunch from the Cyklon second stage rebuild.

Also, thank you again for sending me a spare Cyklon 300 pin. That was in back in 2021!

Erik

Hey -- I am glad that the pin made it to you!

2021, really? Yikes!

No one really likes service kit prices, which recently jumped something like twenty percent in the last year; but they are still cheaper and more obtainable than those of Scubapro.

Now that I think of it, I currently have a few 2980s, that I haven't used for a while, that have four or five year old diaphragms, which still function perfectly. They were great regulators and so cheap to maintain, in the day, with only three o-rings in the first stage and those cool nylon washers in the ports, which lasted for years.

I have a sneaking suspicion why Poseidon got rid of those, in later models . . .

 

[happy-diver]

Renseal

I've bought double hose diaphragm fabric to replace German resin coated canvas diaphragms

Single hose first stage stuff, insertion rubber from any rubber shop for me