oxygen concentrators

[waterlaz]

I wasn't sure if I should write this here but I hope it is ok.

Doug,

I've searched for an oxygen concentrator in Ukraine and this is how things look like:

Almost all shops in Ukraine sell some sort of rebranded "Healicom 7F"(something chinese, idk) line of oxygen concentrators. Usually these are 7F-3 (3lpm) and 7F-5 (5lpm) models.
The 3lpm models are from 13000uah and the 5lpm models are from 16000uah.
I've called a couple of shops that had lower prices on their websites but it turned out that they had not updated their websites yet.
Used Healicom 7F 5lpm are sold for about 7000-9000uah.
There are lots of Healicoms(rebranded as Biomed, Armed etc) here, so I guess it is possible to find them cheaper.


Other used concentrators:
Devilbis 5lpm - 14900uah (The seller claims that it has been in use for 5000-7000 hours out of 30000)
Airsep Visionaire 5lpm - $350 (I havn't called this guy, not sure if this is the real price. The ad sais the concentrator has been used for 40 hours only)
Invacare Perfecto2 5lpm - 600eur (less than 1000h in use)
AirSep New Life Elite - 13500uah


This is what the market looks like. If you find these prices acceptable, I will dig deeper into this.

PS note that $1 is about 25uah now.

[waterlaz]

Does anybody know a good source of used oxygen concentrators in Germany besides the German ebay? I will be visiting Dresden in about a week and thought I might bring one home.

[waterlaz]

I've bought a devilbiss 525 ks oxygen concentrator. However, my torch doesn't really work properly with it. It appears that I don't get enough pressure. The oxygen flashback arrestor is my first suspect right now.
Do you use them when brazing with an oxygen concentrator?

[waterlaz]

Ok, it works a bit better without the flashback arrestor but still not nearly good enough. I used to set my regultor to about 200 kPa for oxygen before and the concentrator provides only about 60 kPa.

[waterlaz]

I've put back the flashback arrestor and removed the injector from the torch. Works A LOT better. Now looking for your advice if what I've done is such a terrible thing.

[Doug Fattic]

Evgeniy, I don't believe there is any need for a flashback arrestor on the oxygen concentrator because there isn't a lot of pressurized oxygen inside. There isn't that much oxygen in the bladder inside the concentrator to explode if a fire went up the hose.

Haven't I read somewhere that there is some kind of difference between the pressures needed for torches used in Europe (and other countries) and American torches? It seems like Truls Johnsen has explained this somewhere. I use a Devilbiss 515 (an older model than yours) and I can run 2 American torches at the same time on mine without any problem.

[waterlaz]

As far as I understand there are two types of torches: injector torches and equal pressure torches. I have an injector torch that requires high oxygen pressure.
I couldn't find any reliable info on Smith AW1A. In fact, all I could find is this quote from some welding forum: "Most industrial oxy fuel torches are or equal pressure design ( Victor, Smith, Purox , Harris etc )"
If Smith AW1A is an equal pressure torch it would explain why it works.

[jclay]

It's equal pressure. Modern torches are. Injector systems are an artifact of the acetylene generator era that preceded widespread availability of acetylene in cylinders and at useable pressure.

Acetylene generators produced gas at extremely low pressure. Injector torches used higher pressure oxygen and an internal eductor to draw acetylene into the feed stream in spite of the low acetylene delivery pressure.

[waterlaz]

I've drilled my injector with a 1.5mm drill and it works like a charm!
1.jpg
The drilled injector.

2.jpg
The drilled injector screwed into the tip next to an untouched injector.

[jclay]

It should. By drilling out the eductor (injector) you turned it into a, more or less, equal pressure torch!

[Scheisserad61]

I am kinda /sorta familiar with all the benefits of Propane and using a Concentrator.

I was wondering if using something like Propylene / Chemtane would use less Oxygen and allow for safely running a bigger tip size, if needed ? Can you get a welding supply place to fill a portable BBQ type tank with the "enhanced propanes" ?

Thanks to Doug Fattic and everyone who has added so much to this discussion !

[Andrew R Stewart]

I am kinda /sorta familiar with all the benefits of Propane and using a Concentrator.

I was wondering if using something like Propylene / Chemtane would use less Oxygen and allow for safely running a bigger tip size, if needed ? Can you get a welding supply place to fill a portable BBQ type tank with the "enhanced propanes" ?

Thanks to Doug Fattic and everyone who has added so much to this discussion !

I think the safety of "running a bigger tip size" is largely the skill of the builder. Not the chemistry of the flame. Andy.

[Alistair]

I am kinda /sorta familiar with all the benefits of Propane and using a Concentrator.

I was wondering if using something like Propylene / Chemtane would use less Oxygen and allow for safely running a bigger tip size, if needed ? Can you get a welding supply place to fill a portable BBQ type tank with the "enhanced propanes" ?

Thanks to Doug Fattic and everyone who has added so much to this discussion !

The LPG fuels use MORE oxygen than Acetylene (around 20 - 25% more, iirc), not less. It's because of the combustion chemistry. Propane is C3 H8, Acetylene is C2 H2.

You can run a bigger flame with LPG type fuels, because you're not limited by the fact that the fuel has to evaporate out of a storage fluid ie. in the case of Acetylene, it is dissolved in Acetone. This means that the size of an Acetylene bottle limits the max. rate of fuel usage, and therefore the flame size.

Presumably Propane is limited also in the rate that it can change from liquid (under pressure, in the tank) to gas, (in the torch), but from what I've read that limit is quite a bit higher than that of Acetylene.


Alistair.

[waterlaz]

OK. I just have to say this. Buying the oxygen concentrator was the best decision in my life I've made in the past year =)
Turning the torch into an equal pressure torch made adjusting the flame so much easier.

[Mark Kelly]

The LPG fuels use MORE oxygen than Acetylene (around 20 - 25% more, iirc), not less. It's because of the combustion chemistry. Propane is C3 H8, Acetylene is C2 H2.

Alistair.

Yup: Molar ratios are 7 : 1 for propane vs 3 : 1 for acetylene but propane is denser (~2 kg/m^3 @ STP for propane vs ~1.1 for acetylene and ~1.4 for oxygen) so volume ratios are closer, ~5 : 1 for propane vs a little under 4 : 1 for acetylene.

[Tman]

OK, I have a question to add to this thread. I have the chance to buy an oxygen concentrator, guy has 3 different models to choose from. All are 5lpm and the same price. Which one would you choose? Invacare 5 OR Invacare Perfecto OR Devilbiss Sunrise? TIA Trent.

[Doug Fattic]

OK, I have a question to add to this thread. I have the chance to buy an oxygen concentrator, guy has 3 different models to choose from. All are 5lpm and the same price. Which one would you choose? Invacare 5 OR Invacare Perfecto OR Devilbiss Sunrise? TIA Trent.

There are several reasons I like my Devilbiss Sunrise (I have an older 515 model instead of the newer 525) better than my Invacare Perfecto. 1st, the outlet nozzle on my Devilbiss is a brass size B. That means I can screw the end of my brazing hose directly into the concentrator’s fitting. The Invacare has a barbed outlet that requires a bit of clear hose jammed into it that needs a plastic female size B adaptor on the other end. (Make sure you get this adaptor with a barb on one end and a female B on the other when you buy the Invacare.) The brazing hose needs a size B male/male brass adaptor to connect to the B size female plastic adaptor. It will work fine with all the junk needed to attach a brazing hose to a barbed outlet but the Devilbiss is a lot cleaner.

2nd, while both concentrators are rated 5 liters per minute output, they do have a different output ability. The Devilbiss can put out several lpm more (probably around 8 lpm). This doesn’t matter when using Victor TEN tips because 5 lpm is enough. However a rosebud or bigger Meco tip (they consume more oxygen than standard propane tips) needs more oomph.

3rd, the Invacare makes a more annoying screech when you forget to open up the oxygen knob on your torch handle when the machine is on. It is a really loud penetrating noise. This is a safety feature to warn grandma she is not getting oxygen. Furthermore once it starts screeching it won’t stop until the machine is turned off and on again. The Devilbiss will stop making noise when the oxygen line is opened again.

Some things you might also consider are how many hours are on each machine. They all have an hour use meter somewhere. My Devilbiss has over 20,000 hours. I’ve also heard from a concentrator repairman that the more they weigh the better they last. He considers both of those brands to be good.

[Tman]

Great Doug, thanks! You have confirmed what I thought after reading this thread. Appreciate your input and guidance. I will get a chance to look at these sometime this week. Guy is moving right now so I don't know when he will be in town.

[Tman]

Thanks again Doug, just brought home my Devilbiss machine. Guy must have had 50 of them for sale. He bought everything when a local place closed.

[Doug Fattic]

Thanks again Doug, just brought home my Devilbiss machine. Guy must have had 50 of them for sale. He bought everything when a local place closed.

Trent, glad it worked out for you. Is there any information about the seller that can be passed on for others looking to buy? Is he willing to ship? Was his prices fixed or negotiable? Did those in his bunch have varying amounts of hours used? The set up for brazing is fairly straight forward but feel free to ask questions if you run into problems. It might be helpful for others if there are any tips about using them that you can pass along.