Transferring air from 1 tank to another

[Diver0001]

Ok my daughter will be using a 50 cf tank. They are harder to come by and thus more expensive than just an 80. So my question is what do I need to move air from 1 tank to another. Yes I realize it won't fill up as the bleed will stop when each tank is the same psi. Thats ok we are just doing shallow water diving. So if we go for 15 min or 30 min it's ok. But it will come down to why hall 2 50 cf tanks and 2 80's when I can hall 3 80's and 1 50. At 53lbs and 4'6" tall unless she's freezing I bet she sucks down half a 50 in the same time I suck down an 80.

If the cost is a hundred bucks well I guess I'll just buy a 2nd 50 and be done with it. But if the cost is more like $25 then hey that makes sense.

I'll spare you the math but just working it out roughly, if you fill a 1/2 full AL50 from a full AL80 then the pressure in the AL50 (in both tanks, actually) once they've equalized will be roughly 160 bar (or +/- 2300 psi).

This is a rough figure but it won't be too far off in practice.

Is this the kind of pressure you're looking for?

R..

 

[Diver0001]

come to think of it, I won't spare you the math. It's easy enough.

I'm working in bar and litres here because it's easier

a 50cf tank has an internal volume of about 7 litres
an 80cf tank has an internal volume of about 11 liltres

3000 psi is about 200 bar = full

So a 1/2 full 7litre tank has about 700 litres of air in it (7 litres * 100 bar)
The full 11 litre tank has about 2200 litres of air in it (11 litres *200 bar)

Together that's 2900 liters of air

Together the tanks have a combined internal volume of 18 litres

So 2900/18 is 161 odd. or about 160 bar

Which is about 2300 psi.

....

So.... just taking this to the next step. If she breathes down the AL50 to it's reserve pressure of about 500psi = 34 bar then after filling it from the full AL80 the pressure would be

(34*7+2200)/18 or about 135 bar. 135 * 14.5 psi per bar gives us about 1950psi. All rough figures, of course.

Now that you know this you can work it out for any size of tanks or pressure differential.

R..

 

[rcs9250]

By removing the piston and then charging the reg all your gas will escape out of the ambient holes in the reg body. Ambient holes are drilled around the area where the large spring is.
If you want to go with the route using the regs just use a HP hose between the HP ports. The biggest issue that someone also posted was that the orifice size will slow down the transfer. Some regs have larger orifices than others but most of the time the hose end at the reg has a very very tiny hole in it to prevent massive gas loss in the event a hose blows. Gas doesn't have to move at high volumes in a HP hose. It dead ends into an SPG.
One could drill the tiny orifice in the hose end but then you have chips stuck in the hose and the possibility of them at some point getting blown into the receiving regulator. Not a good idea.
Unfortunately there is no cheap way to do it unless you stumble onto something on ebay.
If you do go the regulator route be sure you have a second stage or some sort of manual pop off valve to bleed the system so you can remove the yoke from the tanks.
The simplest equalizer I ever made was a bushing that was about 3/4'' long and each end was machined to fit into the valve outlet. I made a rectangular clamp that captured both valves and held the bushing in place. All this had to be laid down on a reasonably flat surface so everything lined up good and then tighten the assembly. Once everything was tight you open the valves a bit and equalize. The bushing had a screw in it for bleeding air. It was free ( I work in a machine shop). Obviously not the safest thing in the world but it worked. I made it because the dive shop I went to had to have a certain minimum psi in the tank or they had to do a VCI. Typically I just put in enough air to satisfy them.

 

[dumpsterDiver]

Jeez, what a bunch of nervous nellies you guys are. Dumpster, thanks for the classic line "you're gonna put an eye out with that thing" and the exciting embolism story.

Back on planet earth, ever had an o-ring in a SPG blow, or a HP hose? It happens, big deal. What about a tank o-ring? That's another HP leak. There's nothing different about this.

And how did this thread morph into a safe-diving-with-your-daughter thread?

There's a big difference. Have you ever personally seen what a blown LP hose can do to someone's arm? If not, then maybe you should think a little bit on it. I am not concerned about a leak. As mentioned repeatedly a HP port has a tiny orifice, so there is no opportunity to blow a high rate of gas. I've had a few HP hoses pop and it doesn't cause injury like a high flow, LP hose whipping around.

 

[halocline]

The guy's talking about hooking up two regs via their HIGH PRESSURE ports. The LP idea would not work because of the ports in the ambient chamber, (as someone already pointed out) so you'd have a big hiss, kind of like opening a tank valve. No exploding hoses, no embolisms.

 

[shogan]

good point RCS.

I think captain hit the most logical solution very early on in this discussion by using two older tank guages connected via an hp hose.

And using the two hp ports being a slower 2nd choice.

And clearly having a new hose designed for this project and not drug around the rocks with gashes or weakened from age is an important part of this project. .

And as indicated in original post at $100+ I would just buy a 2nd tank and not even mess with the project.

 

[redacted]

I made mine from two spare air fill adapters. Added HP hose and fittings ran about $40 at a local hydraulic shop. Have not payed for a pony fill or top off in about 8 years. It also works fine for equalizing two larger tanks when full tanks are not required.

 

[Damselfish]

But it will come down to why hall 2 50 cf tanks and 2 80's when I can hall 3 80's and 1 50.

Well, it's much easier to carry tanks in matched pairs. And when your daughter grows to the point where she starts helping, 2-50s would be a whole lot easier for her than a 50 and an 80. Actually probably easier than carrying a single 50.

The other part of your original premise is that an AL50 is more expensive and hard to find. So look here, same price they sell an AL80 for. A transfer whip makes sense for some uses, but in this case it seems to be a more complicated/expensive and less desirable solution to a simple or non problem.



Another thought, if starting each dive with part of a 50 works for her, if you really want to do it with one tank maybe get something like a 63 which is not that much bigger or heavier, just start with it filled and do 2 dives on it and skip all this. It will probably be a more useful tank over time. Or heck, get her 2 30-40 cf ponies for a bit less. Start with those filled, small and light, same amount of gas or more, and probably easier to sell later. If her BC can't hold the skinny tank, then you'll have an easier DIY project to mess with.

 

[oxyhacker]

But it will if he doesn't touch a thing inside the regulators, and just connects the HP ports together using an adaptor that screws directly into the HP port. Then the regs are still unaltered and usable as regs, and a 2nd stage can be left on to act as a bleed valve.

One can make an adaptor to connect NPT hoses to the HP port on a regulator out of a $1 brass compression fitting from the hardware store and an O-ring. Details in the book. I used several old regulators this way when I started out mixing, and they worked fine.

I also have a minsicule traveling whip, made from a little 10" long flexible grease gun hose (it being the smallest and cheapest hose I could find rated for HP) and two such adaptors, very useful for occasional use like putting some pressure in tanks when one arrives, and weighs almost nothing.

That won't work.

 

[rcs9250]

I am not absolutely positive but I believe you can remove the SPG and the spool out of the gage end of the HP hose in both regs and use one of these. here

I would have to look at one tonight to verify. If the hose end is 37 degree like the fitting, it is the absolute easiest and cheapest way to transfer.
In my case if the angle was not the same I would just put the proper angle on it at work.
It would not have to be stainless . Steel is more than adequate. If you keep it in your save a dive box it would be a good idea to use stainless.
I'm thinking the transfer rate through the tiny holes in the reg end would be acceptable and would make it kind of foolproof so as not to fill to quickly by accident.

Randy