20-11-06

Pumping helium through a personal compressor (English)

The easiest way of blending trimix is by partial transfilling from storage bottles.
However, once the supply pressure drops it gets hard to get enough pressure in your dive tanks.
Especially with the expensive helium it gets very ineffective after a while since it’s getting very hard to remix anything and it becomes necessary to just empty your tanks before blending it again… which is a waste of perfectly good gas.

One solution is a booster pump, but they tend to be quite expensive and slow once the storage bottle pressure gets low.
You can also get adventurous and try pumping it with your compressor… which is what I do.
Doing this is not hard.
The hardest part is providing the helium to the compressor.
There are several ways of doing it ranging from bleeding the helium into a garbage bag, or filling via an old demand regulator… and supplying that to the compressor intake.

However I use an industrial pressure regulator.
These things can be bought fairly inexpensive from your local gas supplier.
Mine had an integrated flow restrictor and a l/min readout for argon and CO2.
I removed the flow restrictor since my Bauer Junior needs a lot more flow than the reg. could provide.
Now the flow meter becomes a normal IP pressure gauge with no flow restrictor anymore. (but still has the l/min scale)

From the regulator I fix a 2m piece of 18mm flexible garden hose.
This will transport the helium to the compressor and act as some sort of buffer to dampen the pulsing nature of the compressor intake.

For fixation I shoved a smaller hose made thicker with duck tape inside the garden hose and clamped it down… Not an elegant solution, but it works regulator_640






 

On the other side I shoved a piece of aluminum pipe with an outside diameter of 20mm into the hose and clamped it down.
This pipe fits perfectly into the compressors (Bauer Junior) intake without the need of O-rings etc.

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Now it’s time to get pumping…

What I do is turn the IP adjustment of the regulator all the way down…
Then I open the storage bottle all the way…
The first gauge should read the storage bottle’s pressure.
The second should read “0”
Insert the pipe with garden hose into the compressor intake.
Now adjust the IP slowly to “some” pressure… I use 1 bar overpressure…
The first time it takes a little trial and error to find the sweet spot, but the idea is to start the compressor and immediately adjust the IP to somewhere above “0”… because the high compressor flow will cause a severe pressure drop inside the hose and you don’t want the compressor “sucking” on your regulator creating a vacuum and wearing your compressor out, thus you need to slightly increase the IP of the regulator and therefore  increasing the flow so that there is a slight constant atmospheric overpressure in the hose.
You will see the needle bounce a little bit up and down above the “0” point on the scale, this is the setting you want…

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Once you have figured out the sweet spot, you can set the IP to this setting next time before you start and not have to adjust any more.
In my case it is around 1 bar overpressure, or 8l/min on the second gauge scale…
After I start the compressor the needle drops to just above “0”

To stop I first pull off the hose from the compressor intake, shut it down and close the storage bottle’s valve.

I also use this setup to boost argon… In fact all the pictures on this page are while topping off my small argon travel-buffer.
However, with argon the compressor tends to heat up pretty fast and I limit pumping only by starting with a cold compressor and limit times to 10min max… which is enough to top off the small 10l cylinder I use for transfilling it into my dive argon bottles.
After which I let the compressor cool down completely…
Don’t forget to let the compressor run a couple minutes after pumping argon to flush out all the argon or you will pump it into your diving cylinders next time, and argon seems to be very narcotic.
I found the compressor doesn’t heat up much when pumping helium, but the electric  drive engine gets very hot when pumping high pressures for a long time like +250bar…
Also the compressor flow begins to stall indicating the helium starts to bypass the final stage plunger…
!!!Watch the intake regulator during pumping!!!
You will notice the IP creep up because of the compressor flow reduction…

I generally don’t find a need to pump helium higher than 200 bar… so it doesn’t present a problem.

It is also advisable to use synthetic oil in your compressor…
Normally all recent compressors come with this oil, but old types may still have mineral oil which can’t stand as much heat as synthetic oil and will break down faster.
BEWARE: usually you can’t just drain the mineral oil from your compressor and pour synthetic oil into it…
Please refer to your manual for proper oil change procedures.

Filling this way has made logistics a lot simpler and more efficient.
Now I can pump helium on top of an existing mix and top it off with nitrox from my continuous blender…
But even without a nitrox stick it is still very efficient since O2 is cheap and being able to scavenge every bit of helium helps; also only having 1 storage bottle in stock keeps bottle rental down…

BEWARE:
Don’t be tempted to start pumping pure oxygen through your oil lubricated compressor!!!
Chances are it will go up in flames with a big bang!!!

And always keep an eye on your setup when pumping helium/argon.

Happy boosting.

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11:42 Gepost door Davy in dive gear projects | Permalink | Commentaren (1) | Tags: blending |  Facebook |

Commentaren

Interesting write up on boosting helium, Thanks. I have been reading up on the subject today. I will be picking up helium tomorrow and will be filling my inspiration dil bottle.
Since writing this article have you made any changes, or still using as shown in the post?
Thanks Again, Al

Gepost door: Al Fossum | 22-09-08

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