Trimix gas blend

[TheRedHead]

I have the "Oxyhacker" book and know how the math works. I also have a card for many free Nitrox fills from the LDS. And I also realize the real solution is a compressor.

 

[cool_hardware52]

That's the problem I wrote about earlier. The LDS will not top off tanks. They don't want anything to do with helium. And yes, it would take a lot of fills on the HP tank to a lower pressure tank to fill a tank. So there is not any easy solution to the problem aside from a compressor.

And finding an LDS that will top off tanks is not a useful solution in my area. They don't.

I have the "Oxyhacker" book and know how the math works. I also have a card for many free Nitrox fills from the LDS. And I also realize the real solution is a compressor.

If you get 32% at low cost you might consider just filling the tanks you want to dive with 32% and "Topping" with He. You'd need a booster and some means to drive it (shop air compressor) Might be cheaper, easier, take up less room etc than having your own OCA compressor, or CB setup. Just a thought. Just get a "short fill" on the 32.


Tobin

 

[TheRedHead]

If you get 32% at low cost you might consider just filling the tanks you want to dive with 32% and "Topping" with He. You'd need a booster and some means to drive it (shop air compressor) Might be cheaper, easier, take up less room etc than having your own OCA compressor, or CB setup. Just a thought. Just get a "short fill" on the 32.

Thanks, Tobin, this sounds like an idea worth investigating. I don't feel comfortable having a cylinder of O2 around with children. So I can get a Home Depot compressor, but where does one find the booster?

 

[JeffG]

Thanks, Tobin, this sounds like an idea worth investigating. I don't feel comfortable having a cylinder of O2 around with children. So I can get a Home Depot compressor, but where does one find the booster?

This is the compressor we used.

 

[cool_hardware52]

Thanks, Tobin, this sounds like an idea worth investigating. I don't feel comfortable having a cylinder of O2 around with children. So I can get a Home Depot compressor, but where does one find the booster?

Ebay, TDS, the usual places. If you are planning on boosting only He, you don't need a O2 clean booster. Many DIY boosters are very capable of boosting inerts.

Tobin

 

[dl348]

How 'bout we stick to the original question at hand. I believe it was a trimix blend poll.:no

 

[texdiveguy]

How 'bout we stick to the original question at hand. I believe it was a trimix blend poll.:no

I will 2nd. that!!!

 

[theskull]

Lets see , a nice 100 foot or even a few more dive , being less narked , longer NDL , faster off gassing , other than the price , why wouldnt you want that ???

For a nice 100 ft. dive. When I use trimix, 100 ft. is the END I prefer, so to put helium in the tanks for a 100 ft. dive would be a waste of money. Also, would require a separate inflation gas, would unnecessarily increase the risk of any unplanned ascent, and would still require a separate inflation gas for my next top-off.

For a nice 100 ft. dive I'll go with air or EAN 32. Just because I am certified to use helium doesn't mean I feel a need to breathe it on shallow dives. It gives me another option for my deeper dives.

theskull

 

[MikeFerrara]

Define HP for the tanks you are thinking about. 3500?

For a 130 cf tank that is rated to 3500 psi has 26.92 psi per cf. If you took a 130 cf containing 32% and filled an AL80 cf tank, rated at 3000 psi, with 32% you would only be able to fill the tank to 1750 psi. That's 65 cf out of your HP 130 cf tank. That only leaves you with 65 cf left in your HP 130 cf tank and your AL80 is only has 46.67 cf in it. At that when the O2 cools down in the tank you can expect a 10% loss in pressure, which would leave you with about 42 cf of 32% in your AL80.

Not very many fills at all. Interested in the math of how I figured that out?

rated tank pressure/rated tank volume = psi per cf

HP130 = 3500psi/130cf = 26.92 psi/cf

AL80 = 3000psi/80cf = 37.5 psi/cf

Difference in pressure between HP130 and AL80?

3500 - 3000 = 500 psi

When will the tank pressure equalize in the tanks?

1500 psi = half of the pressure of an AL80

500 psi / 2 = 250 psi.

1500 psi + 250 psi = 1750 psi.

How much volume does that leave in each tank?

HP130 = 1750psi / 26.92psi/cf = 65 cf

AL80 = 1750psi / 37.5psi/cf = 46.67 cf

This is not correct. Note that 56 cf in the 130 plus the 46.67 in the 80 only totals to 111.67 cf. You lost 18.33 cu ft someplace. LOL

The easiest way to do it...

P1 V1 + P2 V2 = P3 V3...where volume is the actual volume in cf

assuming a 130 is really a 130 and an 80 is really an 80 (rather than a 77 or something). We have...

3500psi * 0.546 cf + 0psi * 0.392cf = P3 * 0.938 cf
Sove for P3 and you get 2037 psi

Lets check it. ok?

2037 psi in an 80 gives 2037psi/3000psi * 80cf = 54.32 cf
2037 in a 130 gives 2037psi/3500psi * 130cf = 75.66 cf
75.66 cf + 54.32 cf = 129.98 cf. ok a little rounding error but we have it all.

 

[texdiveguy]

This is not correct. Note that 56 cf in the 130 plus the 46.67 in the 80 only totals to 111.67 cf. You lost 18.33 cu ft someplace. LOL

The easiest way to do it...

P1 V1 + P2 V2 = P3 V3...where volume is the actual volume in cf

assuming a 130 is really a 130 and an 80 is really an 80 (rather than a 77 or something). We have...

3500psi * 0.546 cf + 0psi * 0.392cf = P3 * 0.938 cf
Sove for P3 and you get 2037 psi

Lets check it. ok?

2037 psi in an 80 gives 2037psi/3000psi * 80cf = 54.32 cf
2037 in a 130 gives 2037psi/3500psi * 130cf = 75.66 cf
75.66 cf + 54.32 cf = 129.98 cf. ok a little rounding error but we have it all.

Gee fellows, my PST HP130 is only rated 3442psi........