Oxygen Transfill whip - digital or analog?

[Warren_L]

Hello everyone, not sure which forum this topic would fit in, however, this is as good as any I suppose.

Question for anyone with experience in gas blending. I've been doing my own gas blending for a while mostly nitrox, up to 100% oxygen. The facilities that I use have a digital pressure gauge which makes it easy to control the flow rate. And with oxygen, I have a heathy respect for the dangers it presents and I take no chances when it comes to filling oxygen.

However, here is my dilemma. I am going to be transfilling oxygen from a larger tank to my smaller rebreather tank using a transfill whip. I have a choice of getting one with an analog gauge or one with a digital gauge. The digital gauge is going to be significantly more than the analog one. By an extra $500 or so. Question is whether flow rates can be consistently controlled in a safe manner using an analog gauge or is it better just to bite the bullet and get the digital gauge?

 

[cool_hardware52]

Hello everyone, not sure which forum this topic would fit in, however, this is as good as any I suppose.

Question for anyone with experience in gas blending. I've been doing my own gas blending for a while mostly nitrox, up to 100% oxygen. The facilities that I use have a digital pressure gauge which makes it easy to control the flow rate. And with oxygen, I have a heathy respect for the dangers it presents and I take no chances when it comes to filling oxygen.

However, here is my dilemma. I am going to be transfilling oxygen from a larger tank to my smaller rebreather tank using a transfill whip. I have a choice of getting one with an analog gauge or one with a digital gauge. The digital gauge is going to be significantly more than the analog one. By an extra $500 or so. Question is whether flow rates can be consistently controlled in a safe manner using an analog gauge or is it better just to bite the bullet and get the digital gauge?

This question has no one right answer. How do you quantify an unknowable potential increase in safety? It's a "Pay your money, take your chances" dilemma.

I'd point out that the smaller the tank being filled, the more difficult it is to control the rate. RB tanks are typically range from small to tiny.

On the digital gauges I've used you can set the display to update once per second. One PSI per second = 60 psi / minute. Nice.

I've seen a number of analog gauges used to fill small tanks, without a problem, but my first choice would be a digital.


Tobin

 

[boydski]

Question is whether flow rates can be consistently controlled in a safe manner using an analog gauge or is it better just to bite the bullet and get the digital gauge?

Hi Warren,

You can control the flow rate when transfilling Oxygen using analog gauges ( I do this with my Masterline Booster ), it is just easier to do with the digital gauge. If you are looking at a $500 in cost between an analog gauge and a digital gauge, it might pay to look at an alternate source.

You can pick up an excellent digital gauge at NE Scuba for $200, and there are versions available for as little as $100.

Good Luck,

 

[Warren_L]

Hi Warren,

You can control the flow rate when transfilling Oxygen using analog gauges ( I do this with my Masterline Booster ), it is just easier to do with the digital gauge. If you are looking at a $500 in cost between an analog gauge and a digital gauge, it might pay to look at an alternate source.

You can pick up an excellent digital gauge at NE Scuba for $200, and there are versions available for as little as $100.

Good Luck,

Hi Boydski, are you able to confidently control fill rate at 1 psi/sec or thereabouts? I'm not certain how to do it, as when I fill regular air, I can hear it flow. But when I fill oxygen at proper rate, I can't hear anything.

Do you have a link for those gauges?

Warren

 

[loosebits]

The smallest tanks I fill with O2 are 40's so I think an analog guage is fine. Wouldn't touch a 6 or 13 with one.

 

[boydski]

Hi Boydski, are you able to confidently control fill rate at 1 psi/sec or thereabouts? I'm not certain how to do it, as when I fill regular air, I can hear it flow. But when I fill oxygen at proper rate, I can't hear anything.

Do you have a link for those gauges?

Warren

Hi Warren,

I use a needle valve to control the flow rate, so 1 psi/sec can be done. I typically fill slightly faster than that (otherwise a deco bottle would take 50 minutes to fill), although I'm certainly not advising speed with oxygen.

You can find a nice Dwyer Gauge at NE scuba (actually, you can buy the whole whip there). A less expensive version can be found on page 543 of the McMaster Carr catalog ( www.mcmaster.com) , although having used both, I much prefer the Dwyer Gauge for accuracy and ease of use.

Good Luck,

 

[rescuediver009]

I think that while the 1 psi per second is a good guideline, it is important to keep in mind that this will represent different gas volumes for different size cylinders. Thus, I think that if you hear the gas moving it might be a little to fast. I think that an analog guage will suffice seeing as you can always slow down the rate if you can physically see the needle moving.
Dive centres use the digital guage moreso for percision rather than control flow rate. As a blender you know that the amount of oxygen added controls the end mix very precisely.

Hope this helps.

 

[Warren_L]

I think that while the 1 psi per second is a good guideline, it is important to keep in mind that this will represent different gas volumes for different size cylinders. Thus, I think that if you hear the gas moving it might be a little to fast. I think that an analog guage will suffice seeing as you can always slow down the rate if you can physically see the needle moving.
Dive centres use the digital guage moreso for percision rather than control flow rate. As a blender you know that the amount of oxygen added controls the end mix very precisely.

Hope this helps.

Daniel - the issue here is that if the needle isn't moving and I can't hear it, I don't know if it is filling or not, as well it is still possible that the fill rate is too fast even if it can't be heard. I'd rather err on the side of caution. Even if it means spending a bit more money to do so.

 

[rescuediver009]

I suppose that developing a complacency in this game is less than ideal. I can totally understand where you are coming from, however with a 2.5" gauge, if you can see it moving ever so slightly, I would think that you are in about the right range.

I think that at this stage it becomes an opinion based matter as to whether you are comfortable doing it the way you do it, because that is all that matters. And we all know that no matter how we do things there will always be someone out there who thinks we should be doing it differently (their way).

 

[karstdvr]

60 psi per minutes kind of fast for a rebreather O2 tank which won't be a large tank.