Aqualung Legend LX First Stage Failure at depth

[lexvil]

As you said, the Sherwood SR design is pretty vanilla. A piston is a piston. But where Sherwood has excelled is in its dry designs. It caught a lot of flak over the years for its bubbling, and that filter in the base of the piston was classic for getting gunked up by naive technicians who smeared silicone grease everywhere, thus killing the reg. But it was still unique. And Sherwood's Bellevue washers are a very sturdy way to balance the design. Classic!
The SR-1/2 approached dry design differently, using an approach I hadn't seen in decades, but I can't remember which other regulator it was:
There is an environmental chamber that seals the area behind the piston. Instead of ambient water pressure pushing on the back of the piston, there's a cylinder that gets depressed by a secondary environmental sealing diaphragm, which has three thin legs that pass through the wall of the reg body, and come out against the back side of the piston. I sure wish I could remember the old brass reg that had three pins that did the same thing. In any case, it's an ingenious throwback technique to sealing a piston that is very underappreciated. And the piston itself has a HUGE bore. In fact, it's a two part piston that's assembled at the time of service, because the overbalancing head with the knife edge is too large to fit through the bore where the shaft seals. Instead, the shaft is inserted in the reverse direction and mated to the piston head at the time of reassembly.

@Luis H , can you remember which old piston had those three transmitter pins in the wall? I'm wracking my brain!

Anyway, without piling up too much on @Jiminy , the Sherwoods are very underrated. They just don't market well on the West Coast. The SR's had a brief issue with turret bolt torque, and the SR-1 second had a brief issue with the spring catching, but that was fixed in the -2 with a simple metal washer. Great regs! There just aren't as many of us out West here with service experience.

Not having seen one in person, the SR 2 looks a lot like an Atomic in pictures.

 

[rsingler]

Well, we've pretty well derailed @databob 's thread on the Aqualung ACD problem, lol!

 

[JackD342]

Are you thinking of the Sherwood SRB3100 series that used 3 pins?

 

[rsingler]

Are you thinking of the Sherwood SRB3100 series that used 3 pins?

YES! Way to go, Jack! Yes, that's the one!
I guess they didn't pirate anybody's design, but resurrected their own concept, with a dry chamber and environmental diaphragm.
I remember when I took the SR-1 service class, commenting that it was a "diaphragm piston", lol!

Yeah, the 3100 just used those pins as a quick way to adjust IP on the piston, as I recollect, instead of disassembling and adding shims. I wonder what smart engineer had a light bulb go on and used the same force transmission concept to transmit ambient pressure to a dry spring chamber. Very cool.

 

[JackD342]

YES! Way to go, Jack! Yes, that's the one!
I guess they didn't pirate anybody's design, but resurrected their own concept, with a dry chamber and environmental diaphragm.
I remember when I took the SR-1 service class, commenting that it was a "diaphragm piston", lol!

Yeah, the 3100 just used those pins as a quick way to adjust IP on the piston, as I recollect, instead of disassembling and adding shims. I wonder what smart engineer had a light bulb go on and used the same force transmission concept to transmit ambient pressure to a dry spring chamber. Very cool.

It was an externally adjustable piston. Including a design for the locking set screw on the adjusting cap that is best described as “you have to be kidding me!”
I had one come through the shop last year. After replacing a couple of internal parts, got it working back to spec.

 

[rsingler]

It was an externally adjustable piston. Including a design for the locking set screw on the adjusting cap that is best described as “you have to be kidding me!”
I had one come through the shop last year. After replacing a couple of internal parts, got it working back to spec.

Wow! I didn't realize you could still get parts. It's from the '80's, isn't it? I always figured those pins would be a sure lock up from verdigris corrosion. At least the SR's use plastic pins which, though they might break, at least won't corrode inside the wall of the reg body.

 

[JackD342]

I don’t remember for sure what parts I replaced, I think the main spring, and maybe even the piston. After initial adjustment the cap was hanging on by only a couple of threads and I didn’t trust that to last. I did NOT come out ahead on my labor charge versus time spent troubleshooting.
Not everything is still available, but I think every generation of piston can still be had.

 

[JackD342]

Wow! I didn't realize you could still get parts. It's from the '80's, isn't it? I always figured those pins would be a sure lock up from verdigris corrosion. At least the SR's use plastic pins which, though they might break, at least won't corrode inside the wall of the reg body.

I would say probably yes to the 80’s. No copyright on the 3100 scan, but the 3200 scan includes a Technical Bulletin dated 1988 about a running change to the piston.

 

[Diving Dubai]

As @Diving Dubai will tell you, the ACD is very nice to have in sandy environments to keep foreign material out. And rental guys love them, in case a knucklehead doesn't put the cap back on before rinsing the regulator after diving. But you're right - there was a flaw there that demands some attention.

When I purchased my 1st Legend, I had no idea about the ACD - it wasn't' a selling point (I brought all my starter dive gear from one shop at the same time)

Years later, I'm still a fan of the ACD. I have non-ACD regs as well, but the level of security the ACD give to my diving is hugely beneficial. Whether it's changing tanks on a moving boat, rinsing my regs at the same time as student, with the risk of them being submerged, and crappy sandy conditions , All give them a superior level of confidence.

To be fair I converted mine to Din early on, and while the ACD can't suffer the same failure, the dust cap on an A clamp is superior in it's fitment. My Apex regs have a screw on cover - which in comparison to the ACD is a faff to locate, screw on and off etc. Not a huge faff, but when you dive every week it gets tedious (especially when hunting for the caps because you put then in a safe place)

The ACD issue we had here appears to be a "perfect storm" in that faulty service procedure in conjunction with a small hole on a tank insert.

I've been diving convertible cylinders for over 5 years - I've never seen a 6mm insert, not even at the dive centre. I know because I have a huge selection of hex keys to cover every eventuality additional to those on my dive tools. Never had to use a 6mm, And I suggest I've been exposed to more convertible cylinders than most.

This side of the water, the main brands are AL, Apex, ScubaPro, Cressi & Mares. The Atomic Titanium is occasionally stocked to satisfy those who attribute price to quality. Others like Oceanic and Dive-Rite stocked by those dealers who can't get access to main brands. Brands that may be well known in the US not known or dismissed this side of teh world

I do have the security in AL/Apex and SP that anywhere in the world my wife and I travel to we can get them sorted if there's a problem. Whilst Brand X may have similar internals to a main brand, try telling that to a service tech who doesn't want to touch something they don't' know.

Both my Legends and my Apex get used hard. They may go a week with nothing more than a quick sprinkle with a fresh water hose, get left on cylinders over night, or thrown into a dive bag wet to go to another dive centre the next day. They get pushed far beyond their service intervals all while performing flawlessly

So while I respect people's aversion to risk, it should be remember that all equipment can be subject to poor service practices but is you want a bomb proof reg, have ADC on a DIN.

 

[Yellowdog]

I have read this thread with interest as I have both Titan LX and Legend LX 1st and second stage regulators that fall within the AL service bulletin serial numbers. I had both sets serviced at Diver's Supply in early December 2018 before reading this information. Can I assume that since both reg sets were serviced by an authorized dealer after the bulletin was issued that the ACD yoke system has been properly tightened to the recommended torque specification?