Compressing Helium Mixtures

[iain/hsm]

Can't seem to find a good answer to "What percent of helium is safe to run through a compressor?"
Any input for those who actually know would be appreciated.
thanks

They say never answer a question with a question but this is an exception so I will add two more as I’m sure most if not all of us would like to know.
First off why does an oil lubricated scuba air compressor run so hot with helium.
Second and why do those folk that say it’s no problem, do it for such a little while then go silent.
But in answer to the original question you won’t find a “good” answer but hopefully only a correct one
and it’s that answer that no one wants you to hear.
For every one else just simply read the label on the compressor or in the manual where it states: Gas. Helium.

 

[Wookie]

Is my masterline not a compressor? It doesn’t seem to get hot with hours of helium compression.

 

[Vicko]

Really? Just have a service head kit to hand and a twin pack of seal kits on the side and know how to use them.
Again and again and again so much so after a while it will become second nature. That or just use it for pure oxygen.

Really?

Shop next to ours also uses it and they had almost no problems in the last 500+ operating hours, runs helium and 100% o2 on it. Ours only has 200 hours on it and just got a overhaul, doubt it will give us much trouble in the forseable future.

 

[iain/hsm]

Heat is an issue with high Helium percentages. We pumped tube-trailer quantities of pure Helium and HeO2 with less than 6% Oxygen on saturation diving systems. The best compressors we found for continuous duty had water cooled interstage heat exchangers. You can just monitor head temperatures for the small quantities recreational and rebreather divers would use. Add a big fan and stop pumping for a while if necessary. A non-contact Infrared temperature gun would be a good investment.

Akimbo.

The DSV helium gas transfer compressor your describing is a million miles away from a scuba diving air compressor. Having said that its just the same engineering principle offshore and you couldn’t use that Gas Transfer Kelly tube trailer compressors for Helium Chamber/Bell recovery or gas reclaim. Two completely different animals.

That said I’ve seen offshore so called professional divers plumb the heat exchangers back to front (twice) and wonder why the gas gets so hot so fast LOL. Here’s the build list: DSV Tosia Palladin, DSV Ocean Commander, DSV Endevour, DSV Cal Dive, DSV Bibby Sapphire using both He transfer and recovery.

 

[iain/hsm]

Is my masterline not a compressor? It doesn’t seem to get hot with hours of helium compression.

No its a single stage booster pump with two heads, you are describing, Now I'm not sure if you have the U101 seal kit fitted and the ceramic discharge valve or if your using the brown bronze filled PTFE seals. No matter
your using the term "Masterline" as a brand name and expect everyone to guess the model type and build specification.
Non the less its a booster not a compressor.

In addition now if you want a booster built for helium you get ring changes and valve changes you also get a two stage design. That curly wire is attatched to a RTD on the dischage side of the second stage that gives you the gas temperature HOT off the 2nd stage head onto a digital display of temperature on the front panel.
The gas is measured HOT before cooling for good reason.
Not cold as you have described after wizzing around that finned 1/4 bore cooling coil attatched to a darn big fan.

Here's one I built earlier for a client two stage double acting with modifed head and high temperature cut out switch and digital temperature display. 240VAC 50Hz

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The helium build design used a larger Nickel Bronze modified 1st stage head coupled with the smaller standard stainless 2nd stage head as a two stage design.
63mm Gauges (with pulsation frits)
RTD Temperature control
Hi temp cut out (hot side final stage discharge) prior to heat exchanger
Reduce bore tubing to instrumentation for oxygen safety
Gas flow direction bypassing Gauge line on branch tee for oxygen safety
U101 helium/oxygen seals
“Mirror smooth” valve castings and ceramic seals with bronze liners and Monel Springs
Gas Pulsation Dampning interstage
Safety Relief Valve (ported)
TEFV Motor Eff2 IP 54 rated (not drip proof)
Ported Vent HP
All piston liners were bronze "cupped" (not stainless on stainless) to reduce stainless friction fire risk.

 

[iain/hsm]

Really?

Shop next to ours also uses it and they had almost no problems in the last 500+ operating hours, runs helium and 100% o2 on it. Ours only has 200 hours on it and just got a overhaul, doubt it will give us much trouble in the forseable future.

Really.
200 hours and your overhauling it already!!! Your kidding right, and have missed another zero off those numbers
Most of us in the diving industry wouldnt need change an filter at 200 hours let alone a rebuild overhaul.
Look a typical compressor designed for helium runs 8500 hours between service.
A typical small 2cfm oxygen compressor 4000 hours
The dive shop next to you runs 500 hours
Shoot even Woolie will claim 500 hours for his Masterline
Your bringing up the rear dude at 200 hours
That or you ain't doing it so right.

 

[Wookie]

7000a2. O2 booster. Yes, I get 500 hours. I’m at 1200 hours, no issues yet, but I do keep a spare seal kit handy.

 

[iain/hsm]

7000a2. O2 booster. Yes, I get 500 hours. I’m at 1200 hours, no issues yet, but I do keep a spare seal kit handy.

The 700A2 is a single stage double head design each with an identical head but plumbed for two stages of compression but still using Two Identical stainless steel heads for both the 1st and 2nd stage.
100mm gauges
No Temperature control
No high temp cut out
U104 seal kit
Stainless piston and liners

Would be interested to see those piston and liners when you finally get around to change out the seals for scoring and scuffing metal to metal especially in a oxygen rich environment. I guess your waiting for the seals to fail before changing the rings. As you say "No issues yet".

 

[Akimbo]

The DSV helium gas transfer compressor your describing is a million miles away from a scuba diving air compressor.

No question. The point I was trying to make is that there is a significant difference in heat transfer on compressors pumping high percentages of helium; regardless of the system. Other that leakage, all those problems ultimately translate to heat and taking extra measures to manage heat buildup can prevent premature failure. Production operations like sat systems or gas plants manage the problem with added cooling capacity. That cooling capacity can be integral to the compressor design or added to the system by increasing heat exchanger capacity at the head and/or between stages.

A private/garage operation can manage the problem with increased cooling and/or intermittent operation. Of course that requires the ability to measure temperatures, typically at the head or outlet of each head. This general principle applies to any system from a single stage pneumatic booster through multistage piston and metal diaphragm compressors.

 

[iain/hsm]

A private/garage operation can manage the problem with increased cooling and/or intermittent operation. Of course that requires the ability to measure temperatures, typically at the head or outlet of each head. This general principle applies to any system from a single stage pneumatic booster through multistage piston and metal diaphragm compressors.

Akimbo.
No way near can a dive shop even get close using a standard oil lubricated scuba air compressor for helium.
Name your brand of choice Bauer, Mako, Coltri it makes no difference. Stick helium in a scuba compressor and you’ve got so much helium “blow by” whistling Dixie out the crankcase breather from past the piston rings, making the compressors interstage compression ratio rise into double digits, So much that if the loss of helium alone leaking out the thing don’t put the scuba shop lot off I don’t know what will.

Maybe your increase in head temperature may do it, who knows but once it is approaching that of the planet Venus and oil breakdowns so fast at the discharge side of the valve your left wondering why the funny metallic taste after the dwell time “shoot through” across the chemical filter tower bed.

Better they read the label on their compressors it’s an Air compressor and leave it at that.
But measuring head and metal temperature with a IR gun on a silver metal reflective surface is no way close when what you really need to know is the gas temperature and the oil vapour temperature across the discharge valves before cooling and not the colder metal casings and tubing surrounding it.

A can of matt black high temperature spray paint on the reflective may give a better reading.Then again the lucky ones may get sleepless night once ignorance makes way for reality.