In the Weeds with the Poseidon Jetstrream / Xstream Niederdruckmanschette . . .

[Bigbella]

Much like a contractor whose kitchen remodel is never quite complete, my gear is often the last in line for repair.

Both were heavily-used Jetstream second stages which required attention -- one from my day-to-day gear, and the other, part of the Atmosphere full face mask, the "PP" (positive pressure") version, which uses similar Xstream guts, and adds a "check valve," basically, a thin silicone gasket, to the top of the valve housing nut (#4951), for good measure.

While disassembling both second stages for the ultrasonic cleaner, I had forgotten that my Jetstream still had one of the older brass / silicone -- get this --"Niederdruckmanschette," or "low-pressure cuffs," (#3440) which most of the world still calls the damn thing.

The main difference between the older versus newer "second stage valve insert" was in its construction -- whether of a more conical brass model with a pinhole opening (seen right); or an extruded plastic of some form -- and the presence or lack of a sintered white filter at the hose end -- intended to further clean the breathing air of particulates. Both had similar silicone sheaths.

The older model never possessed any filter -- though I hadn't noticed any real differences between the two, and wondered whether anyone else with some of that older gear, had noticed anything?

 

[Fibonacci]

Very interesting... I also recently acquired an older Jetstream with the machined metal inner.

After an ultrasonic clean and replacing all the o-rings I pressurised it on an XStream MK 3 and noticed far less initial hiss as the Valve Insert bladder filled and sealed against the LP Valve housing vs the more modern style #3440 with integral sintered secondary filter.

I then compared my recently overhauled XStream primary with a new Valve Insert, vs the octo with a thoroughly cleaned (I thought...) Valve Insert... there was a noticeable difference in hiss between the new and the old insert as they pressurised.

So it seems like #3440 should routinely be replaced at major overhauls...
The first stage air is well filtered at the tank, I wonder why (apart from cost) they changed from a machined metal inner with no filter to an injection moulded inner with bonded integral secondary filter?
The benefits would have to outweigh the risk of another potential failure point if the very fine secondary filter became clogged?

 

[Bigbella]

So it seems like #3440 should routinely be replaced at major overhauls...

Weirdly enough, I have never replaced any of my own, since none of them ever appeared cut or damaged; though I once did see the aftermath of what could happen to that silicone piece, in the event of a first stage failure.

It had been extruded through the tiny vents of the LP valve housing, like strands of capellini . . .

 

[Fibonacci]

The worst silicone sheaths I've seen so far had tiny dimples where they had started to extrude through the fine air bleed holes.

I recall on the Tekna 2100 we used to have trouble if you ever disassembled the inner barrel as the small diaphragm also developed these dimples and would never line up perfectly on reassembly, causing annoying leaks unless you replaced it routinely.

So I'm wondering if a similar situation could occur with the Poseidons, the small dimples on #3440 would also never properly line up with the air bleed holes on reassembly, and cause an increased 'hiss' as they initially pressurised before deforming and sealing?

 

[Bigbella]

So I'm wondering if a similar situation could occur with the Poseidons, the small dimples on #3440 would also never properly line up with the air bleed holes on reassembly, and cause an increased 'hiss' as they initially pressurised before deforming and sealing?

The only time that I had ever seen that "dimpling" -- aside from some gear that I had serviced for others -- was when I had the Oceanair / Thor with the 2940 first stage; and the original IP for that model was 12.5 bar -- 3.5 bar (about 50 psi) more than what is currently specified.

That old brass 3440 is as good as new and I had often wondered whether that dimpling was just the product of an improperly cranked IP?

 

[Fibonacci]

~snip~
That old brass 3440 is as good as new and I had often wondered whether that dimpling was just the product of an improper IP . . .

Every used Poseidon I've bought has had wildly different IP from spec, including both the XStream Mk 3s which should have 8.5 BAR so perhaps a very high IP could easily start it extruding?
I found one Jetstream with the rear edge of 3440 folded over itself, must have been dislodged as it was pushed home dry (I use soapy water when assembling) but by the look of the deep crease it had been used that way for years!

 

[rsingler]

The older ones were/are great. The new filter doesn't "filter" as much as it gives additional passageways for servo valve air pressure if there's crud in the input. The problem with the old one was a pinhole that could corrode shut if there was salt-water induced verdigris. The new filter is obviously bigger, but with the necessary flow restriction.

As for the silicone bell, the "capellini" is indeed a function of prior IP. And as noted, if the pimples don't line up on reassembly, the valve leaks. My replacements with new have been because the silicone split, usually at the neck that slips over the conical pinhole. I don't know of a source for replacements, and haven't tried taking apart a blue one to see if it fits over the old carrier.

 

[Bigbella]

The older ones were/are great. The new filter doesn't "filter" as much as it gives additional passageways for servo valve air pressure if there's crud in the input. The problem with the old one was a pinhole that could corrode shut if there was salt-water induced verdigris. The new filter is obviously bigger, but with the necessary flow restriction.

I am glad that you chimed in -- that bit about the purpose of the "filter" was from an old foreign catalogue entry, "Inside [3440] is a small sintered filter [which] becomes clogged with rust particles when using unclean air."

Yeah, sure . . .