Drager Jets

[David Parker]

I have always calulated out the burn time by working out the volume of gas in my cylinder & dividing it by the flow rate. ie 150Bar X 10Lcyl = 1500L of gas divided by 15.5 for 32%jet = 96.77Min

How is this effected at depth ??

(my gas does not seem to go quicker at depth, why is this?? when physics say it should ????)

Cheers
Dave

[Odin]

Doesn't change it - and why use the 32% jet?
It guzzles gas!
Search for articles by Freelow.
He dives a dolphin and has written some good stuff (even got a bit on my experiments in one of the articles!)
Enjoy it!

[David Parker]

the 32% jet was used as an example only ever used it once, ps. it was the only one I could remember ??

Dave

[Odin]

Try this...
Semi Closed Rebreather diving gas calculations.

[David Parker]

Originally Posted by Odin

Try this...
Semi Closed Rebreather diving gas calculations.

Its not what I am looking for. What I want to know is will my cylinder empty quicker at depth like open circuit but through the jet? as stated above. I use this calc I got off a spread sheet I downloaded. however it seems to work out even at depth but I can not figure how it does this? unless I just can not see the difference?

Dave

[David Pye]

It isn't depth dependent - the flow rate through the jet should be constant regardless of the depth you're at.

Your oxygen consumption doesn't vary at depth, so why should the flow rate of the injector?

David

[David Parker]

would the gas be subject to depth thou ie. the deeper the more gas would flow through all be it compressed ie.

at surface pressure the 32% jet would be delivering 15.5 L per min

at 2 atmospheres the 32% jet would be delivering 15.5 L per min but the gas compressed 2 times.

so will I burn more gas at depth?

[David Pye]

No, according to my understanding (which isnt 100% certain, I've not dived an sCCR), the gas flow of the injector is constant.

Which means that the gas throughput through the jet remains EXACTLY the same regardless of depth, and so your gas utilisation will not change based on depth, unlike open circuit.. I would assume that the regulator was like the O2 reg on the KISS, in that it has a fixed IP, and is not compensated for by depth but as I've not trained on them, I'd wait for someone else to confirm!

David

[Neil McLeod]

Which means that the gas throughput through the jet remains EXACTLY the same regardless of depth, and so your gas utilisation will not change based on depth, unlike open circuit.. I would assume that the regulator was like the O2 reg on the KISS, in that it has a fixed IP, and is not compensated for by depth but as I've not trained on them, I'd wait for someone else to confirm!

This is correct. So long as the supply pressure is at least twice the downstream pressure then the sonic valve will deliver a "constant" mass of gas. The Cylinder gas consumption can be calculated in exactly the way outlined in the original post. The First stage is not depth compensated as stays at about an absolute IP of 17+1 Bar; so unless you take the unit to 80-ish meters, or so, expect it to work as planned. One other caviat - the IP will fall slightly once the cylinder pressure reaches about 30 Bar.

Other useful but reassuring facts: Each Sonic valve is in fact a double. If either blocks then the other should still add O2 containing gas such that if the VO2 is less than about 1.5 L/min then a hypoxic mix is avoided. Further, if a disaster occurs and both were to be blocked the IP will rise and the Second stage is then designed to leak fresh gas into the loop. This along with the system acting as open circuit reg. (if you flush the loop) should allow the remaining primary gas to be used before going to bailout. (just a further escape option so long as you know the loop PO2.)

Neil

[Freeflow]

The Dolph has a CMF design of jet-Constant Mass Flow. If you look at your first stage you will see that there is no diaphragm or holes into it to take into account the ambient pressure of the water.

The 32% jet is a waste of good nitrox. If you have a pO2 meter you can work out your vO2 [Oxygen consumption] and then tune your cylinder gas to a slower flowing jet, I use 40% through the 60% jet to get maximum extention [down Amy-Ward], although this will lean the mix I breathe to 30% under a heavy workload.