Depth uncompensating MK17

[Packhorse]

Is there such a thing? can you modify a MK17 to make it uncompensating for depth?
Are there any SP regs you can do this to?

 

[herman]

Why would you want such a reg, the thing would breath hard at depth. No manufacturer has ever made one, why build a reg that gets worse as you decend when allowing it to compensate for depth is so easy to do. It would be fairly easy to modify any reg so it would not compensate for depth but I can see no reason anyone would want to.

 

[redacted]

From a conceptual engineering standpoint it might seem easy. From a user modification standpoint, I believe it would be quite difficult to eliminate or seal up the ambient pressure sensing mechanism.

 

[do it easy]

Don't rebreather divers use blanking plugs and orifices in their SCRs? Could you just use something that is a combination of a blanking plug and a CWK so that there was no ambient pressure transferred to the main spring? It would essentially make your reg into a backwards overpressure relief valve. I think it would be trial and error to set it, but it might work.

Why would you want such a beast?

 

[Packhorse]

Why would you want such a reg, .

For a rebreather.
KISS style RBs inject a constant amount of gas in to the loop regardless of depth. This is acheived by a Constant Mass Flow Oriface (CMF) which is just a small hole that will let a certain amount or gas to pass. (very) basicly if the input pressure is more than twice that of the output pressure the amount of gas that passes will be constant. Increase the input pressure (more depth on a standard reg) and the flow increases.

No manufacturer has ever made one,

Thats not true. Only (most but not all) regs used for scuba need to be depth compensating.


The Apeks DS4 is a popular reg for RB's and there are solid "plugs" readily avaliable that replace the environmental diaphram to disable the depth compensation.
Alot harder on a piston style scuba reg. But should be fairly easy on most diaphrams. I just havent heard of any other regs apart from the DS4 that has the part avaliable.

 

[bythesea]

I think you might get a better answer on RBW. The majority of people here are going to be skeptical if only because they don't know about regs set-up for CMF as opposed to depth compensating. I have an Oxycheq blanked. The environmentally sealed Zeagles should work. You could probably use an old Poseidon 300 by making a filler plug and a cold water rubber on the first stage. The DS4 is so popular because you can get the blanking plug from Martin at Tecme. I believe there are people using older sherwoods. Theres a guy in Nevado who regularly sells the 1st stages on Ebay for about $180. I think I'll toss out a post there and see if we can get a complete listing of whats been tried. It would be good info for a homebuilder sticky.

PS If you were up here in the Northeast instead of on the bottom of the planet I'd say use the 17 for diluent as it's got a good rep for high flow and good freeze protection which obviously isn't such a big deal on the O2 side of the equation

 

[Packhorse]

Thanks bythesea. All my regs are scubapro so I would like to stick with them.
Reason for asking here is I am hoping DA my chip in with his wealth of info on SP regs.

If I cant use a SP I will go with a DS4

 

[wedivebc]

Is there such a thing? can you modify a MK17 to make it uncompensating for depth?
Are there any SP regs you can do this to?

I believe this is the reason ISC switched from SP regs to APEKS on their meg rebreathers after they introduced the COPIS

conversion is pictured here Waters Edge

 

[DA Aquamaster]

The Mk 17 is a pretty typical diaphragm design in terms of how the spring adjustement pad operates. To remove the depth compensating feature all woud have to do is replace the flexible external diaphragm with a rigid metal one and seal it or perhaps solder or brave it to the groove where the flexible diaphragm usually seals. It would all be covered by the trim boot so looks would not be a big deal.

On second thought, it would be even simpler to just remove the white plastic piece that transfers pressure to the interior and put a fairly thick (1/8" or so) round brass plate in it's place. I'll have to look tonight to see if there is lip for it to rest on. If so, it would support the external diaphragm and prevent it from moving inward and rupturing while the diaphragm woudl stil provide a very reliable water and gas seal.

An old Mk 3, Mk 5 or Mk 10 the SPEC kit is another option as the small ambient pressure holes would be very easy to fill. You would also want to seal around the base of the swivel cap to prevent any gas or water leakage through the threads. A thin rubber washer or perhaps a small (1/16") diamter o-ring would probably work. The problem with using a piston reg is that the Ip is harder to adjust and for a CMF situation, the flow can be adjusted either by changing orifice size or by changing the IP. Adjusting the IP is potentially a more precise way to make flow adjustments and is easier to accomplish with a diaphragm design.

 

[Packhorse]

Thanks DA.
I would like the mod to be reversable so soldering/brazing is out of the question.
I assume you cant use a MK16 as it is not environmentally sealed?