Gas Booster questions

[Capt Jim Wyatt]

I need to make my gas blending more efficient. Currently I am PP blending nitrox & CF filling Trimix. I am not pleased with the CF method for various reasons.

A gas booster would solve some of the problems with the CF & PP blending. I know next to nothing about boosters other than the theory behind how they work.

There are practical questions I have regarding their use. One of the boosters I am looking at has a volume of 6.2 in3/cycle. Generally speaking what is the cycle rate of such a booster?? 1 cycle per second?? If it is 1 cycle/sec I come up with about 4.5 scfm for the booster, which is adequate for me, I think.
http://www.steammachines.com/ae2-Haskel.asp This one is $2500 new.

Does this booster seem adequate for filling say 3 or 4 sets of double 100 FT3 tanks a few days each month & maybe 15 80FT3 nitrox bottles per week?

Thanks in advance...
Does anyone have any better suggestion as to the type/model pump in this same price range? Any ideas where I can get one?

[Uncle Pug]

what is the CF method?

I use continuous blending for both trimix and nitrox.

[Capt Jim Wyatt]

Its the method I set up about 9-10 months ago with pressure regs on the He & O2 bottles.

I have yet to be able to get the flow rates to be consistent. The percentages just fluctuate. When I make a change in the regulator pressure the resulting % takes several minutes to show up on the He & O2 meters.

You helped me a LOT with this when I set it up & your help got me as far as I did get...but the lag time between changing flow rate & the resultant indication on the meters causes me to run around like a ckicken with its head cut off.

The other thing is...last week I was filling 6 sets of double 120's and the compressor got hotter than I was comfortable with....If not for the compressor getting so hot I would consider trying to tweak my system.

Uncle Pug--thanks again for your help last year when Scott Klopin & you helped me set this up.

[Uncle Pug]

OK... now I remember... CF = CB :D
Jim, I know that Omar was toying around with analyzing pre-compression... and it is true that post compression analysis has a lag time of several minutes... but... once you get it set up it shouldn't fluctuate back and forth... it will change with the fill pressure but you can allow for this.

I have tape on my ball flow gauges marked with the starting points for the various blends I want. I might waste a little gas just to make sure that it is where I want it but once set I rarely adjust.

What I have found is that ambient temp seems to affect where I must set the ball on the tape to begin with. So I fudge one way during the winter and another during the summer. Where you live that shouldn't be a problem. :D

I try to make the dial-in setting by bleeding off enough gas to get xxxxpsi (whatever is the median pressure between start and end) on the manifold so that during the fill, mix variation from low to high pressure will offset itself.

Nitrox is a snap. Trimix takes a little fiddlin' since increasing the HE requires you to also increase the O2 and the same with decreasing either.

As for compressor heat... I can't remember what compressor you ended up with but I have a fan blowing on the front of my RIX. I am waaay past the projected run time for changing out my 3rd stage rings (all I pump is nitrox or mix) and I attribute that to the extra cooling fan.

Some days I am filling two sets of dbl 104s and the bank of three 250cf (3500psi) and the temp never goes up beyond what I can touch the first stage cylinder head with my finger... this is my scientific test for okey dokey status.

Questions???

[Capt Jim Wyatt]

Mine is not a Rix .. and I am starting to fret over that fact--particularly flowing O2 into it.

I think if I did more fills I'd find those setpoints - but I just don'd do that many fills over a period of several months.

[Uncle Pug]

Omar uses an IR type 30 (I believe) and he, as well as others felt that I would not get good service life out of the RIX... so far so good.

Anyway...

The solution might be for you to set up a Bank for your nitrox since that is what you are doing the most of and that is also easiest to blend. You are only adding 11% O2 to get EAN32 so that isn't that big a deal. When I fill our deco bottles with EAN50 I PP blend using O2 and EAN32 from the bank.

For your trimix fills you might not be adding very much O2 (depending on your He%) so that shouldn't have you fretting either. You are using the correct oil?

What are you using for flow meters after the pressure gauges on the O2 and He bottles?

And what mixes are you usually dealing with?

And is it feasible for you to set up a bank?

[Capt Jim Wyatt]

we are using a high grade of synthetic oil. And I use a Dwyer flow-meter and flow the gas into the meters at 2 LPM

18/40 is the usual mix...doing banks may not be feasible .. yet.

[Uncle Pug]

Capt Jim Wyatt once bubbled...
we are using a high grade of synthetic oil. And I use a Dwyer flow-meter and flow the gas into the meters at 2 LPM

18/40 is the usual mix...doing banks may not be feasible .. yet.
Try an extra cooling fan and fiddle with it some more. You are not adding much O2 into the intake to get 18/40.

When you wrote "flow the gas into the meters at 2 LPM"... did you mean "into the analyzers"?

You are using flow meters between the O2 & He regs and the blender???

[Capt Jim Wyatt]

Yes--flow meters between O2/He bottles to intake/blender

and 2 LPM flow to the analyzers, yes.

[Uncle Pug]

I think you should fiddle with it a bit more... especially try to get the extra cooling thing going. What compressor did you get?

And start looking for some storage cylinders! :D

[omar]

Jim,

As you are aware heat is a killer for compressors. As UP suggested an additional fan would do wonders to help cool the compressor. As he also mentioned, I didn’t select a RIX because of the supposed maintenance and durability issues of the third stage. If I get another unit I will strongly look at a RIX. Interestingly, the ANDI site has a couple of I-R type 30’s, which is what I use, for sale.

As for the continuous blending stuff. You need to have a little patience and trust that the marks you have set for the percentage are correct. Constantly tweaking the flow for the gas addition will cause it to jump around and it seems that you can never get it just right. This is somewhat common with units that have low output and fairly sizable filtration setups.

Renting or even buying some storage tanks is a heck of a lot cheaper than a booster. With storage tanks you can bank the gas you want and it also allows you to figure out the correct flow rates. I don’t run my compressor for filling individual sets of doubles, I wait until the bank is down and I have tanks to fill and then run the unit all day. I now bank a bottle of 30/30 and 2 of 21/35. If I need a higher helium content I can usually just add some helium to the tanks directly and then top with either of the storage mixes. I have found that this is the easiest and best way for my trimix blending needs.

I have got a setup where I analyze the mix right after the blender and before the compressor in addition to after the compressor. There are some differences between the two that I am working out. I expect that I will have them figured out in the spring. (I am not doing a lot of diving right now).

As for boosters I would look at an electric drive unit. This way you will not need a second high volume compressor to drive the booster. FYI, there are 1728 cubic inches in a cubic foot so a output of 6.2 in^3 @ 1 cycle a second will get you 0.21 ft^3 per minute. A very slow process. As for boosters you get what you pay for.

omar