Surface Supplied Tank Diving

[Ingolf]

I have a question regarding a tethered dive i want to put together.

I have a 6.5 Cubic meter breathing gas tank i want to keep on land/boat. and have a 50-75 foot air line running to my regulator.

The primary regulator is a standard high pressure gas regulator capable of reducing 5,000 psi down to anywhere from 1-500 psi.

I figure if i dont go any deeper then 10-25 feet (which i know i will Not) then i don't see a reason why i would need a balanced first stage regulator to make any adjustments if i manually set my incoming air supply to my second stage reg at somewhere between 130-160 psi. It would be immediately reduced to 130-160 coming out of the bulk tank so my 75 feet of 300 psi operating pressure hose should handle it, and at 3/8 diameter i think the air supply would be more then adequate.

Does anyone see any issues with this or anything i am overlooking? I am seeing this as basically a hookah diving setup except im not running low pressure.

 

[spectrum]

So what is this proposed first stage? Is it as reliable as a scuba product?

You are talking hookah which runs low pressure to the diver's 2nd stage delivery valve.

 

[GrimSleeper]

I have a question regarding a tethered dive i want to put together.

I have a 6.5 Cubic meter breathing gas tank i want to keep on land/boat. and have a 50-75 foot air line running to my regulator.

The primary regulator is a standard high pressure gas regulator capable of reducing 5,000 psi down to anywhere from 1-500 psi.

I figure if i dont go any deeper then 10-25 feet (which i know i will Not) then i don't see a reason why i would need a balanced first stage regulator to make any adjustments if i manually set my incoming air supply to my second stage reg at somewhere between 130-160 psi. It would be immediately reduced to 130-160 coming out of the bulk tank so my 75 feet of 300 psi operating pressure hose should handle it, and at 3/8 diameter i think the air supply would be more then adequate.

Does anyone see any issues with this or anything i am overlooking? I am seeing this as basically a hookah diving setup except im not running low pressure.

If you're keeping the first stage on the tank on the boat, it doesn't make the slightest difference whether it's balanced, unbalanced or set pressure - a SCUBA first stage simply adds a set intermediate pressure to ambient pressure, and in the scenario you describe the ambient pressure on the first stage isn't going to change, since it's not going underwater. So, as long as your chosen second stage is ok operating in the intermediate pressure range you describe, it should work as long as you are operating in the sort of depth range you describe.

My big concern would be that you don't have any way of checking pressure remaining in your supply tank, unless you've got a gauge on the first stage and plan to have someone on the boat monitoring it with some way of signalling you.

Oh, and Spectrum's right - since you're describing supplying low pressure to a second stage, it doesn't really make any difference whether you're doing it with a hookah compressor or a big tank and a reg, what you're doing is essentially hookah diving.

 

[spectrum]

If you're keeping the first stage on the tank on the boat, it doesn't make the slightest difference whether it's balanced, unbalanced or set pressure - a SCUBA first stage simply adds a set intermediate pressure to ambient pressure, and in the scenario you describe the ambient pressure on the first stage isn't going to change, since it's not going underwater. So, as long as your chosen second stage is ok operating in the intermediate pressure range you describe, it should work as long as you are operating in the sort of depth range you describe.

My big concern would be that you don't have any way of checking pressure remaining in your supply tank, unless you've got a gauge on the first stage and plan to have someone on the boat monitoring it with some way of signalling you.

Oh, and Spectrum's right - since you're describing supplying low pressure to a second stage, it doesn't really make any difference whether you're doing it with a hookah compressor or a big tank and a reg, what you're doing is essentially hookah diving.

Grim sleeper...

You are confusing depth compensation with balancing. (Been there, done that)

Balancing maintains IP across the range of cylinder pressure. An unbalanced regulator will have some tolerable effect.

With the cylinder and 1st stage topside the regulator will not be able to depth compensate. For the shallow depths mentioned its immaterial, if the second stage is taken deeper it will eventually become objectionable.

Pete

 

[GrimSleeper]

Grim sleeper...

You are confusing depth compensation with balancing. (Been there, done that)

Balancing maintains IP across the range of cylinder pressure. An unbalanced regulator will have some tolerable effect.

With the cylinder and 1st stage topside the regulator will not be able to depth compensate. For the shallow depths mentioned its immaterial, if the second stage is taken deeper it will eventually become objectionable.

Pete

Probably just failing to make myself clear... It's not unkown. By -

So, as long as your chosen second stage is ok operating in the intermediate pressure range you describe, it should work as long as you are operating in the sort of depth range you describe.
​

I meant exactly what you've said : ie. "for the shallow depths mentioned it's immaterial". When I said

If you're keeping the first stage on the tank on the boat, it doesn't make the slightest difference whether it's balanced, unbalanced or set pressure ​

I meant that the reg won't compensate for depth, but within the shallow range Ingolf describes and the constant pressure he expects to get from his reg, the set-up he proposes will work.

I think we're both actually saying the same thing. I'm just not saying it very concisely.

 

[spectrum]

Understood. I commented since it will make the "slightest difference" just not a significant one.

Pete

 

[Fishpie]

What 1st stage pressure reducing regulator are you proposing?
Does it flow enough gas to support a diver?

 

[Ingolf]

I tried it out this weekend, went down to about 10 feet and played around for a few hours. Worked fantastic. I only had it set to 60psi and the air and that was more then enough

 

[Rich Keller]

As you have already found out it is not a problem. What you may want to do is add a life line to the hose making a small umbilical so as you move the stress is on the line not the hose. Also consider how you are attaching the umbilical to yourself. A simple quick release snap shackle on your harness would be the best way to go.