Interesting discovery - DS4 LOW Ip settings stable!

Genesis

Here's an interesting one folks....

Fooling around with some DS4s today, working hose routing and such for the K1.

I have been curious about their stability at LOW IPs. Why? Because for Oxygen, a very low IP makes a lot of things easier to handle. A stuck injector, whether solenoid or otherwise, is less dangerous in that the gas flows much slower. Low IP means less fire risk on the secondary side of the reg and downstream from there (doesn't do anything on the HP side of course)

Most regs can be adjusted over a relatively narrow band. But the DS4s adjustment is the large nut inside the balance chamber, which bears on the spring and ultimately the diaphram. The actual force on that nut is not very high, all-told (if it were it would rip right through the diaphram itself, of course)

Anyway, I decided to see how low I could crank it down, whether there were stability problems with it set low, and what the limits were mechanically.

I'm not sure exactly where the limits are - but I achieved STABLE performance at 40psi, while retaining enough clearance for the pressure transducer (the black disc) to go back in and work properly, along with the environmental seal and cap!

I do not know if there is a potential problem actually trying to use it set up this way as of yet, but it doesn't look like it.

This looks like a fairly significant safety improvement all the way around. Yes, I realize that setting up like this makes the O2 and Dil regs non-interchangable, but they're not anyway in that if one goes south you're not diving in any event (you need both) and the hose setup is going to be different in any case.

Thoughts?

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Scuba_Vixen

One of the advantages of low IPs is that the solenoid draws less current to open, the catch 22 is that it has to stay open longer. Surge current versus battery drain is what you have to work out the pros and cons of. I'd be inclined to stay with IPs around 100# or so, where everything generally works as predicted. .... But who knows, you may be onto something.



Darlene

nigelh

What range of depths was it stable over? We use the unsealed ones on the Inspirations as the sealed ones apparantly fluctuate at depth. I've never thought to dive with an IP gauge fitted.

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nigelh

Genesis

The sealed ones are "overbalanced" and thus will add more than the actual "depth" at depth. The reason is that the black disk is of a slightly larger diameter than the active area of the diaphram.

However, with the adjuster backed off this far I suspect there will be a problem when very deep because the transducer will impact on the adjuster, and thus no longer adjust.

This could be solved easily by going to US4s, of course, which have no transducer, but are unsealed, or leaving the black cap and "window" out but screwing the end cap back on (basically making a DS4 into a US4) You would then get ambient adjustment only with no "overbalance."

The real advantage seems to be the much lower risk of a PO2 runaway before you can deal with it with the lower gas feed pressure and thus slower addition. There's basically no time I can come up with where you NEED to pop the PO2 up fast (I'll leave off a blow-up ascent since you're not supposed to do that in the first place!)

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

dave t

I exeperimented with low IP's on my inspiration (ds4) and had two solenoid stuck open incidents. one at 50m and one at 65m. I think that as the solenoid is an upstream type there wasnt enough pressure to close it. I was running about 3-4bar and I know that sounds like plenty and maybe it was coincedence but after uping the IP to 7bar it has never happened again

HTH

Dave

Genesis

Interesting.... will see how it all works out.....

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

Ben Field

Not sure of the relavence but just in case its of interest....

The machines I work on in the food industry use solenoid ejectors, very much like rebreather solenoids, I have 160per machine to play with so get a good idea how they react to varying feed pressures.

If the pressure is too low they either don't shut (freeflow) or don't shut fast enough (over ejection for me, too much O2 for you) high IP makes them jam open but thats not an issue here.

Worst of all is when they shut, albeit slowly, then creep open alittle again as the pressure dosen't back up fast enough behind them, this leads to a slow trickle which is inaudible in a factroy and simply leads to air starvation, in a Rebreather situation with would have the effect of turning an ECCR into a KISS without you or the electronics knowing.... not sure that would be a good thing?!

(Our machines run at a somewhat different rate to Rebreather admittedly, solenoids have a life of 1billion+ cycles at over 1000 ejections per minute, the machines use between 25 and 100 litres of air per second when working flat out.)

BEN

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nigelh

I've just spent quite a while looking at the exploded view of a DS4 and I can't see this. To get a pressure step up/down you need a seal between the two 'pistons'.

Maybe I'm being dumb and missing something but unless the ES diaphragm stops moving freely I don't see a pressure difference to cause "overbalanced". I assumed the problem with errors at depth was something becoming tight and adding a new force.

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nigelh

Genesis

Its actually intentional on the DS4s, if you believe Apeks. I can think of a number of reasons why it shouldn't overbalance, but it does.....

The solenoid behavior depends much on the actual type of solenoid. There are two general designs - one uses and requires the pressure of the fluid being switched to make the seal, the other does not.

The former have both a minimum and maximum pressure rating, the latter have only a maximum.

I'm using solenoids of the latter type.

__________________
"A venturesome minority will always be eager to get off on their own, and no obstacles should be placed in their path; let them take risks for Godsake, let them get lost, sunburnt, stranded, drowned, eaten by bears, buried alive under avalanches - that is the right and privilege of any free American."
http://www.denninger.net
http://www.diversunion.org/liability.htm - Fix the Diving Cert racket

whoizrob

Low IPs could be nice for people running KISS style valves as you could use a larger orfice. I'd imagine a larger orifice adds a bit of robustness to the system (even with a good filter .003 is a darn small orfice).

From a DIY standpoint I also have a much larger selection of orfices available to me in the larger sizes, .003 being close to the minimum size for cost effective commercially available orfices.

Just a thought...

Rob