Effective DSV designs?

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Fibonacci

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Spun off the previous thread to allow it to keep focus without an interesting sidetrack...:wink:

Just wondering what features experienced rebreather divers look for in an effective DSV?
Most appear to follow similar executions, but specifically I'm wondering:
  • Is the front vertically moving lever style of shutoff valve more intuitive or easy to use vs the rotary knob?
  • Would an additional brightly coloured indicator (easily visible from the rear) be a useful feature?
  • Ease of breakdown for cleaning and transport... most DSV's feature a threaded collar to connect the hoses but these do not always seem to be keyed so that the mouthpiece consistently points in the right orientation on reassembly.
  • Ease of service... uses snap rings and standard o-ring sizes?
  • Should the mouthpiece connection also be modular or are standard cable ties OK?
  • Is a 1.5" or bigger hose connection a disadvantage as it makes the entire DSV more bulky vs gas flow at depth?
  • What current DSV's do rebreather divers rate highly? Drager looks pretty good, but...
 
My personal favorites are a rotary twist compared to a lever (especially those rotary ones that you can extend the knob size, like the Golem or the PSCR-types). I have yet to find a lever that one can easily switch single-handed. A rotary design needs to be REALLY stiff to require two hands. Some lever-actuated ones are ok if they're part of a BOV where you have a large moment arm to brace against in order to flip the switch from loop to OC, simple DSV's like the ISC or SF2 ones are virtually impossible. It also serves as an easy visible indicator that the DSV is open or closed. With a rotary, if it's parallel, it's open, if it's perpendicular to gas flow, it's closed. With a lever, depending on the position, it's not as visible. I even saw one diver attempt to install his loop backwards because he thought the DSV was open based on the lever position, he simply had it upside down and the way it was hanging fooled him for a second. Not a real world issue so much, but it's something to be aware of.

I'm not sure some brightly colored indicator would be worthwhile. I'm not sure it would really hurt anything, but people disregard their HUD's, I don't doubt that they're quickly displace a brightly colored DSV switch from their consciousness.

I like bayonet connectors. They solve the issue of clocking the mouthpiece, ease of assembly and disassembly, and facilitate better loop cleaning since you have full access to the hose, the DSV, etc. A good many are simply hose-clamped directly to the DSV without any provision for ease of disassembly.

Ease of service will depend on the DSV design. Some are easier than others.

I'm not sure what you mean re:modular mouthpiece. All of the ones I've used take a normal mouthpiece and use a standard zip-tie. I personally spread a thin layer of silicone underneath the mouthpiece just to make sure there's nothing that could affect its ability to seal. It's frustrating finding a leak if it's coming from the mouthpiece stem. If you mean modular like the Golem where you can unscrew 4 screws and screw in a p-port adapter for FFM use, I'm not familiar enough with the other manufacturers units to tell you that this is common or not.

As for hose size, a modular one like the Golem or the Divesoft allows you to pick the matching hose nipple for your loop hoses. It's a pain trying to stretch a set of Coopers onto a connection that's too big, I can tell you that first hand. And because they are modular, you can choose loop hoses independent from what the unit is designed to use. I personally like Coopers, so I get the Golem hose nipples for Coopers and don't have to worry about it.

My personal choice is a Golem BOV (I'm a BOV advocate) but if I had to choose a DSV only, it would also be the Golem. I have minimal experience with the Divesoft, and I've heard mixed reviews, although I'm not positive that those were not early models and have had issues ironed out. I made my choice purely based on my own opinions about what is important to me. Other divers may choose something else for their own perfectly valid reasons. The ones I absolutely don't like are the whole barrel twist ones.
 
So a tube within a tube, no orings schlepped in silicone with 4 circlips
within the inner tube exerting pressure against the outer tube for sealing

I use corning 111 which is thick and helps make for a better seal than dive shop wet runny thin silicone
but it makes the DSV more difficult to operate, however if you leave out a couple of the circlips???

same design as the O.M.G. without the screw on hoses

full.jpg


gotta love it, with three circlips missing from previous dumkopfs
without having opened one before I already have plenty spares

full.jpg


what do you actually want to do mate
 
I personally spread a thin layer of silicone underneath the mouthpiece just to make sure there's nothing that could affect its ability to seal.

mate you always say smart stuff, so what's this, use saliva
 
  • Is the front vertically moving lever style of shutoff valve more intuitive or easy to use vs the rotary knob?
    • I think the knob is more intuitive because it's like a normal ball valve. That said, the levers are easier on my mouth because you don't have to control the torque from the mouthpiece. I can never remember on my Meg which direction is open, but it's really easy to use for me. The DSV on my double hose is a twist from the side version and that's a two-hand operation which is no-good.
  • Would an additional brightly coloured indicator (easily visible from the rear) be a useful feature?
    • no.... Granted, I'm a cave diver, so nothing visual can ever be relied on. The Poseidon bov has a rotary lever on the side, but it's second stage is on top which is unique
  • Ease of breakdown for cleaning and transport... most DSV's feature a threaded collar to connect the hoses but these do not always seem to be keyed so that the mouthpiece consistently points in the right orientation on reassembly.
    • I think the bayonets are easiest, but the threaded collars are fine with me. What I don't like is the Meg DSV where it is worm-geared on there which is a PITA
  • Ease of service... uses snap rings and standard o-ring sizes?
    • obviously for o-rings, but they're all standard to some extent. Snap rings SUCK since they require special tools to use properly and since DSV's are usually delrin, the "other" ways to get the off will scratch it to bits.
  • Should the mouthpiece connection also be modular or are standard cable ties OK?
    • Cable ties are fine with me. Sidemount should be able to rotate like the Golem Gear one, and that has the extra advantage of compatibility with a p-port for FFM
  • Is a 1.5" or bigger hose connection a disadvantage as it makes the entire DSV more bulky vs gas flow at depth?
    • no
  • What current DSV's do rebreather divers rate highly? Drager looks pretty good, but...
    • Golem Gear, Divesoft, and Poseidon for me
 
It's not to lube the mouthpiece stem. It's to seal the sealing surface to hedge bets against a torn mouthpiece of a broken zip tie.
 
Is the front vertically moving lever style of shutoff valve more intuitive or easy to use vs the rotary knob?
I like the rotary knob as used on the golem BOV and DSV. I have used the lever type on both ISC and Kiss versions and its smoother and lighter but less intuitive for sure.

Would an additional brightly coloured indicator (easily visible from the rear) be a useful feature?
Not sure what the purpose would be?

Ease of breakdown for cleaning and transport... most DSV's feature a threaded collar to connect the hoses but these do not always seem to be keyed so that the mouthpiece consistently points in the right orientation on reassembly.
The uniquely keyed left and right collars that swivel on the golem are fabulous for cleaning and drying the DSV and allowing airflow through the hoses. I've always been a bit concerned about the single tiny oring seal of these but 4 years in have yet to have one leak.


  • Ease of service... uses snap rings and standard o-ring sizes?
  • Should the mouthpiece connection also be modular or are standard cable ties OK?

The o-ring free design on the ISC DSV is genius. But snap rings are a pita. A screw driver is much more of a standard tool for assembly disassembly. Standard cable tie is fine.


  • What current DSV's do rebreather divers rate highly? Drager looks pretty good, but...

The ISC is a great minimalist design with some smart features to keep you from installing it backwards by accident (a real risk in some). These features were not mentioned your questions but I think they merit serious consideration - making sure that the DSV/BOV or the flapper valves inside are built correctly for the unit is super important.

Also critical is the design of the spiders, the WOB on the flapper valves, the total dead space volume, how water is cleared before opening the DSV, and how a HUD can be attached and HUD position adjusted.

The golem has a superior knob, can be broken apart for cleaning and widely available flapper valves.
 
I have yet to find a lever that one can easily switch single-handed

The Divesoft DSV is lever-style but has a pair of "tabs" that allow the operation to be completed one-handed. To close, you grab the bottom tab with your thumb and then the lever. To open, you grab the top tab with your thumb and pull the lever up. You can obviously flip that and grab the lever with your thumb and the tabs with your hands to open/close as well.

upload_2019-5-23_14-38-53.png
 
Thanks for the detailed replies, very helpful!
Just explaining a couple of my questions more thoroughly... sorry should have been more clear.

@JohnnyC re modular mouthpiece
Yes more like the Golem in that you could swap out a standard mouthpiece module for a p-port version or other variation. Or mount other accessories like a LED indicator etc
.Golem DSV - Ultra-compact high performing Universal Dive Surface Valve (DSV)
Golem Gear, Inc. - BOVs
Is a Scubapro G250 style deflector vane useful or only for DH OC where air at IP would also be venturi-assisted to some extent?

@rjack321
Not sure what the purpose would be?
The bright orange visual indicator idea was just meant to be an additional 'reminder' from the diver's POV... in some other DSV designs they can be partially open or closed and it is difficult to tell at a glance. Most current lever or rotary knob DSV's only indicate their status when viewed from the front, or by feel.

Also critical is the design of the spiders, the WOB on the flapper valves, the total dead space volume, how water is cleared before opening the DSV, and how a HUD can be attached and HUD position adjusted.
Good points, many of the CNC machined spider designs seem to be more oriented for ease of manufacture than minimal obstruction for efficient gas flow.

@tbone1004 agree snap rings can be a PITA and easily mar a soft CNC'd Delrin component unless you are very careful even using the correct circlip pliers! But fine screw threads can also easily get cross-threaded in soft Delrin...

@victorzamora yes flanges on the Divesoft are a good feature, they seem to offer a great deal of customisation of their DSV with different elbows, hose connections and accessory fitment points:
DSV | Divesoft
 

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