Max Helium fraction continuous blend

[tmassey]

Interesting testing. Better your compressor than mine for now... But I too would like to scavenge He too... Could you tell us more about your compressor? brand, number of stages, CFM capacity (or motor HP even). Do you know if your compressor is splash lubricated or pressurized lubrication?

Compressor head temp measuring seems straightforward. How did you measure oil temp or frothiness?

And what was your thinking to go with straight He instead of 21/35 in the stick? You mentioned waste, but it’s not that much — especially if you stop the He just a bit early... It does make it easier to change the blend if there’s problems with the He in the compressor (like selectively leaking out...).

But thank you very much for writing this up! I am enjoying it.

 

[rjack321]

my 3.5cfm alkins has 3 stages and is splash lubed with 751 synthetic oil
it has a oil sump window for checking the level - and/or bubbles

I pump 100% because I can do that at much lower pressures. CBing 10/70 up to 3600psi was audibly hard on the pump. I could hear the blowby and the pistons banging around. Just pumping 100% at lower pressure seems friendlier, no banging, no measurable heat.

 

[michael-fisch]

Take a look on thedecostop.com and search for "Omni Booster". I invented it almost 20 years ago and mine is still going strong.
When I return He tanks they have 5-10 psi in them and I pump helium to 320Bar.

Michael

 

[taimen]

Which compressor you use for this and do you see any significant helium loss?

 

[Valyngar]

Ok well I got a temporary setup pieced together and did some tests. The focus was just to see how much He I could affectively extract from an industrial K bottle and into empty/swept large OC tanks. After which, CB some Nitrox on top to make 21/35.

Before even starting I acknowledged that you can PP several bottles with enough He to accomplish a 21/35 mix so I eliminated that from my waste calculations. I let some locals with CCR’s grab the top off the He K for their little dil bottles. So I started with a K of He at just a smidge above 1k psi.

I also realized I didn’t really need my stick. I don’t need to blend or decant anything so why waste He filling it. I just put together a basic whip to connect the He reg to the compressor, and just used the reg to set flow control on the fly. This might be a little harsh on the compressor on first start and shutdown.

My process wasn’t a fast one but it did work! While pumping the 100% He I monitored compressor head, case, and oil temps closely with a calibrated thermometer and only noted a slight increase in the head of about 20 degrees compared to head temps while pumping air. My oil never got frothy/foamy and was also monitored closely.

After the He was in the tanks I let the tanks stabilize for a few hours and re-rigged the compressor for CB’ing nitrox. All my tank pressures were happy so I started pumping again. Once the first tank was done I was bummed at what the analyzer was indicating. Both O2 and He fractions were way off and the analyzer was constantly changing its mind.

I talked with the owner of the analyzer (loaner from one of lucky RB dil bottle owners) and they said to just let it sit for a few hours and stabilize and check it again. Well that did it. The analyzer was consistently indicating 21.5/37. I guess packing nitrox on top of pure He takes a little while to mix? Maybe stir it next time.

After all was said and done I wasted less than 5% of the He I started with and I’m sure most of that was in the whips. I highly suspect I waste way more O2 in the stick but that’s cheap and needs to be decanted for safety reasons obviously.

for now I believe I have continued to elude buying a booster. Only time will tell how hard this is on the compressor. Hopefully my trimix needs (minimal) won’t lean on it too hard. Last step is going to be to send a few samples off and see what the report sniffs out.

Actually takes about 12 hours to helium mix stabilize. Have been doing checks with my analyser. Remember to put bottles laying and roll a bit.

 

[rjack321]

Take a look on thedecostop.com and search for "Omni Booster". I invented it almost 20 years ago and mine is still going strong.
When I return He tanks they have 5-10 psi in them and I pump helium to 320Bar.

Michael

These are fancier than I need, I use a wine cork with a hole in it attached to a small grocery bag. The cork goes in my prefilter and I just manually keep the bag partially inflated with a drilled out ebay oxygen regulator.

Like you I posted about pumping 100% helium over 10 years ago on TDS, seems like SB is just catching up

Which compressor you use for this and do you see any significant helium loss?

There is no loss of helium from any (modern) oil lubed compressor, rig blow-by is routed back to the first stage inlet.

Don't do this with any oil-less compressor​

 

[taimen]

There is no loss of helium from any (modern) oil lubed compressor, rig blow-by is routed back to the first stage inlet.

Yes, this is what I have always understood. But a lot of confusing comments always pop up. Some of them confuse loss of efficiency with loss of gas. Others seem to be pure misinformation. Anyway, I haven't yet built my He compressor setup.
Are there any real life differences between 3-stage and 4-stage compressors for pumping helium (relatively light use)? And now I am asking about small-ish regular scuba compressors, not dedicated helium compressors which are too expensive.

 

[Miyaru]

...
There is no loss of helium from any (modern) oil lubed compressor, rig blow-by is routed back to the first stage inlet.

...​

Here's an example of a Bauer compressor suitable for pumping Helium:

Any gas escaping in case of over-pressure is routed back to the first stage.​

 

[RayfromTX]

Like you I posted about pumping 100% helium over 10 years ago on TDS, seems like SB is just catching up

I thought I recalled reading an old thread about this when I started scouring all the historical threads on all the websites about these topics as I was getting my system setup.

Indeed, you didn't just talk about it on the other website, you also discussed it here ten years ago. Continuous Trimixing Question

There are some other threads from back then and since then as well.

Also interesting to learn that @michael-fisch invented the omni-booster.

 

[rjack321]

I thought I recalled reading an old thread about this when I started scouring all the historical threads on all the websites about these topics as I was getting my system setup.

Indeed, you didn't just talk about it on the other website, you also discussed it here ten years ago. Continuous Trimixing Question

There are some other threads from back then and since then as well.

Also interesting to learn that @michael-fisch invented the omni-booster.

I gave up on the little hargraves sampling pump pretty quick. It works to route your trimix inlet gas to a helium analyzer (since they rarely have a remote sensor like an O2 cell). but its just not necessary to CB trimix at all when you can pump raw helium and top of with 32%