Question for Dave Sutton

divingtactics · October 10th, 2012, 01:10 PM

Hi Dave,

Having watched your presentation video on YouTube, you mention using the DIL first stage with a lower IP as a manifold via the LP ports to bring off board DIL in using QC6-DESO fittings and a higher IP on the off board first stage. Nice concept, one, I'd like to play with.

Question: How much IP difference would there need to be between the regs? 10 psi 15 psi 20 psi?

Many thanks in advance for such a simple but useful concept.

Jase

Peter L · October 10th, 2012, 02:09 PM

I have done this but biased it the other way aka IP higher on DIL than BO by .5 bar / ~7PSI. I was at the time however using an Omniswivel one way shut-off QC so I am unsure of the DESO impact as it's two way but in the instance of 7 PSI I would find that my DIL would be at .5 bar remaining after a full bailout then it would start taking down the BO tin.

I suspect with a DESO two way connection it would average out the pressures to some extent but that's for Dave to tell as I did not test it this way.

Tiptopperoo · October 10th, 2012, 03:27 PM

What would happen if both first stages were set to the same IP?

Mr Walker · October 10th, 2012, 03:50 PM

Quote: (Originally Posted by Tiptopperoo)

What would happen if both first stages were set to the same IP?

you wont know for sure which tank goes first.

Peter L · October 10th, 2012, 04:07 PM

Quote: (Originally Posted by Mr Walker)

you wont know for sure which tank goes first.

If they were equal IP and no one way valves in the mix then Boyle's law states that they will equally drop pressure on demand.

Simon A · October 10th, 2012, 07:12 PM

You shouldn't need more than 1 bar difference, however check your regulator output pressure with a full cylinder ans a nearly empty cylinder, it is likely to not be the same. this is why regulator manuals when setting the IP also specify an input pressure.
HTH
Simon A

seppu · October 10th, 2012, 10:08 PM

hi
you need less than 0,01 bar.

Hanssing · October 10th, 2012, 10:37 PM

Quote: (Originally Posted by seppu)

hi
you need less than 0,01 bar.

Thats nonsense, and shows you do not know flow-dynamics, nor how a regulator works.
When the gas is flow you will see pressure-drop through the system, and this can cause the regulators to become active. The more flow you have from a regulator the higher the pressure-deviation from its setpoint is, both facts means you haev to have a larger difference.

But its EASY to set. Turn the tank with the lowest pressure off, and look at the SPG while purging from the manifold. If the shut-off tank drops on the SPG, then the difference is too small - simple as that.

Hanssing

Dave Sutton · October 10th, 2012, 11:37 PM

Heck, I just open the valve that's installed at the offboard QD input and turn off the onboard cylinder valve. Makes it completely uinambiguous.

But with that said, unbalancing the regulators works well. The thing I did (do at times still) is to reduce the onboard regulator IP by about 1 BAR, so any offboard bottle can be used. I use the onboard for BOV at surface as well as for dil MAV/ADV and when I get to transition depth I flip open the valve which allows the offboard to backp-feed the first stage and now the offboard feeds BOV, MAV, and ADV. The lowered IP of the onboard is only used shallow, so the performance degredation associated with a lowered IP is not really an issue.

0.1 BAR as suggested "works" in a perfect world, but as flow changes the IP of the supplying regulator will fluctuate by more than that, and it all gets ambiguous again. Plus reguilators creep, and you want the delta P to be enough to ensure a boas towards the higher IP without any ambiguity. 1 BAR seems to work fine. With that said... see what I first wrote. I usually flip the valve, and then reach behind me and secure the onboard bottle valve "just to make sure". Belts and Braces, so to speak.

Dave

.

divingtactics · October 10th, 2012, 11:59 PM

Okay, thanks Dave - understood. I already have all the equipment here and will run a few tests over the next few days at various pressures before actually fitting it on to my rig. It was really to prove a proof of concept for a mate who is running the standard 3 litre cylinders on his rig. I'm using larger 7 litres on mine. I'd be inclined to keep the onboard DIL reg at 9.0 bar and put the offboard at 10 bar. Not sure I like the idea of shutting down an onboard cylinder valve as the QC6's don't have a locking mechanism and then we have a single point of failure if it became disconnected.

October 10th, 2012, 01:10 PM	#1 (permalink)
divingtactics Serious Swagelok Addict Join Date: Mar 2012 Location: Melbourne Australia Posts: 156 Thanks: 17 Thanked 16 Times in 15 Posts	Question for Dave Sutton Hi Dave, Having watched your presentation video on YouTube, you mention using the DIL first stage with a lower IP as a manifold via the LP ports to bring off board DIL in using QC6-DESO fittings and a higher IP on the off board first stage. Nice concept, one, I'd like to play with. Question: How much IP difference would there need to be between the regs? 10 psi 15 psi 20 psi? Many thanks in advance for such a simple but useful concept. Jase
(Offline)

October 10th, 2012, 02:09 PM	#2 (permalink)
Peter L New Member Join Date: Apr 2012 Location: London Posts: 299 Thanks: 12 Thanked 19 Times in 13 Posts	I have done this but biased it the other way aka IP higher on DIL than BO by .5 bar / ~7PSI. I was at the time however using an Omniswivel one way shut-off QC so I am unsure of the DESO impact as it's two way but in the instance of 7 PSI I would find that my DIL would be at .5 bar remaining after a full bailout then it would start taking down the BO tin. I suspect with a DESO two way connection it would average out the pressures to some extent but that's for Dave to tell as I did not test it this way.
(Offline)

October 10th, 2012, 03:27 PM	#3 (permalink)
Tiptopperoo CCRx Supporter Join Date: Mar 2012 Location: Melbourne Posts: 98 Thanks: 21 Thanked 10 Times in 7 Posts	What would happen if both first stages were set to the same IP?
(Online)

October 10th, 2012, 03:50 PM	#4 (permalink)
Mr Walker Relax /Frankie Join Date: May 2012 Location: Karlskrona, Sweden Posts: 204 Thanks: 56 Thanked 54 Times in 36 Posts	Quote: (Originally Posted by Tiptopperoo) What would happen if both first stages were set to the same IP? you wont know for sure which tank goes first.
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October 10th, 2012, 04:07 PM	#5 (permalink)
Peter L New Member Join Date: Apr 2012 Location: London Posts: 299 Thanks: 12 Thanked 19 Times in 13 Posts	Quote: (Originally Posted by Mr Walker) you wont know for sure which tank goes first. If they were equal IP and no one way valves in the mix then Boyle's law states that they will equally drop pressure on demand.
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October 10th, 2012, 07:12 PM	#6 (permalink)
Simon A Duvet Diver Join Date: Mar 2012 Location: UK Posts: 97 Thanks: 0 Thanked 6 Times in 5 Posts	You shouldn't need more than 1 bar difference, however check your regulator output pressure with a full cylinder ans a nearly empty cylinder, it is likely to not be the same. this is why regulator manuals when setting the IP also specify an input pressure. HTH Simon A
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October 10th, 2012, 10:08 PM	#7 (permalink)
seppu New Member Join Date: Mar 2012 Location: rosenheim Posts: 25 Thanks: 5 Thanked 0 Times in 0 Posts	hi you need less than 0,01 bar.
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October 10th, 2012, 10:37 PM	#8 (permalink)
Hanssing New Member Join Date: Mar 2012 Location: Denmark Posts: 72 Thanks: 9 Thanked 4 Times in 2 Posts	Quote: (Originally Posted by seppu) hi you need less than 0,01 bar. Thats nonsense, and shows you do not know flow-dynamics, nor how a regulator works. When the gas is flow you will see pressure-drop through the system, and this can cause the regulators to become active. The more flow you have from a regulator the higher the pressure-deviation from its setpoint is, both facts means you haev to have a larger difference. But its EASY to set. Turn the tank with the lowest pressure off, and look at the SPG while purging from the manifold. If the shut-off tank drops on the SPG, then the difference is too small - simple as that. Hanssing
(Offline)

October 10th, 2012, 11:37 PM	#9 (permalink)
Dave Sutton Banned Join Date: Mar 2012 Location: Union Beach, New Jersey Posts: 1,281 Thanks: 73 Thanked 189 Times in 103 Posts	Heck, I just open the valve that's installed at the offboard QD input and turn off the onboard cylinder valve. Makes it completely uinambiguous. But with that said, unbalancing the regulators works well. The thing I did (do at times still) is to reduce the onboard regulator IP by about 1 BAR, so any offboard bottle can be used. I use the onboard for BOV at surface as well as for dil MAV/ADV and when I get to transition depth I flip open the valve which allows the offboard to backp-feed the first stage and now the offboard feeds BOV, MAV, and ADV. The lowered IP of the onboard is only used shallow, so the performance degredation associated with a lowered IP is not really an issue. 0.1 BAR as suggested "works" in a perfect world, but as flow changes the IP of the supplying regulator will fluctuate by more than that, and it all gets ambiguous again. Plus reguilators creep, and you want the delta P to be enough to ensure a boas towards the higher IP without any ambiguity. 1 BAR seems to work fine. With that said... see what I first wrote. I usually flip the valve, and then reach behind me and secure the onboard bottle valve "just to make sure". Belts and Braces, so to speak. Dave .
(Offline)

October 10th, 2012, 11:59 PM	#10 (permalink)
divingtactics Serious Swagelok Addict Join Date: Mar 2012 Location: Melbourne Australia Posts: 156 Thanks: 17 Thanked 16 Times in 15 Posts	Okay, thanks Dave - understood. I already have all the equipment here and will run a few tests over the next few days at various pressures before actually fitting it on to my rig. It was really to prove a proof of concept for a mate who is running the standard 3 litre cylinders on his rig. I'm using larger 7 litres on mine. I'd be inclined to keep the onboard DIL reg at 9.0 bar and put the offboard at 10 bar. Not sure I like the idea of shutting down an onboard cylinder valve as the QC6's don't have a locking mechanism and then we have a single point of failure if it became disconnected.
(Offline)