$500 Compressor Kit

[joebob24]

How many people would be interested in a $500 kit that you could assemble with basic tools that would produce a compressor capable of something like 3-4 SCFM at 3500 PSI? Motor, filtration and mounting not included. Just trying to gauge interest at this point.

 

[Gone for diving]

The compressor head is rated to 1000 rpm. I just need to get a new pully, so I can get it up to that speed and hit the target 3 cfm. Heat generation is a real concern though, so I have been working on verifying temperatures before I speed it up much.

Sounds like you need a 3phase motor and a VFD

You must be moving enough oil for it to stay together this long...

Are you running it a bit over full?

I have done that on a vintage compressor that I can't get parts for, the oil level is just higher then the bottom of the scotch block,
Quiets up the clicking.

 

[joebob24]

Sounds like you need a 3phase motor and a VFD

You must be moving enough oil for it to stay together this long...

Are you running it a bit over full?

I have done that on a vintage compressor that I can't get parts for, the oil level is just higher then the bottom of the scotch block,
Quiets up the clicking.

Already running a three phase motor with VFD. The motor is only rated to 1745 RPM at 60 hz and I am running it at 120hz. (it is inverter rated, but for some reason I can't find the maximum rated RPM for it) Just need a bigger pully on the motor side. I just looked at the compressor specs again and it has a minimum rating of 655 rpm and maximum of 1000 rpm, so I am pretty close.

It runs surprisingly quiet, other than the cooling air.

The last time I had everything apart there was plenty of oil in the cylinders, so I think it is getting enough. I added holes in the tops of the pistons to allow oil to blow up onto the pistons of the stages from the bottom during retraction.

 

[tmassey]

I haven't posted much about the filtration, because it really isn't the interesting part of the project.

Funny, that’s the part that is interesting to me! Mainly because, assuming the compressor does not actually turn itself into shrapnel, the filtration is the only thing between you and death from either CO or lipoid pneumonia.

Dramatic, maybe, but CO at depth is *much* more deadly than on the surface, and only real cure for serious lipoid pneumonia is a double lung transplant — something that has killed users of questionably-sourced vape…

So I’m glad to hear you have high-grade filtration. As long as you add a blast shield to the process , there’s not much left to hurt you. (The tanks are another story: maybe some sacrificial aluminum tanks? ).

My question is: seeing as the point of this is cheap, and seeing as commercial pressure vessels for filter stacks cost roughly double your target price… What are you using for the pressure vessel for the filter?

 

[joebob24]

My question is: seeing as the point of this is cheap, and seeing as commercial pressure vessels for filter stacks cost roughly double your target price… What are you using for the pressure vessel for the filter?

I am not sure I want to open this can of worms, but I machined one out of 7075-T6. Even after doing all the analysis, which shows the stress way below yield, the filter housings are the only part that I really don't like to be in the same room as. I have it set up so I can blow it down before entering the area.

I think if I didn't have the option of making one, I would buy a replacement filter housing for any of the commercially available compressors. This one is only $310: https://nuvair.com/products/purification/hp/pb-6-05-021.html The kit has the wrong filter element with it, but you get the idea. The correct filter for the same housing is around $35. No matter what you do, you are going to have to shell out some cash for filtration.

Dramatic, maybe, but CO at depth is *much* more deadly than on the surface

I was thinking I should probably get a CO meter to check the air. Any recommendations for one? At some point, I want to send the air out for analysis as well. I found one of the test kits that you send in for $160 ish, which would be worth it.

 

[tmassey]

Funny you should ask…

Forensic Detectors Carbon Monoxide (CO) Detector Review

Like everything I write, this is long and detailed, and you may not need much of this detail. I use a CO monitor both for continuous CO monitoring of my compressor, as well as ad-hoc checking of tank fills I get elsewhere. This is divided into sections so that you can skip the sections you...

scubaboard.com

 

[Gone for diving]

Where is the CO coming from,?
As long as there is no engine around, and using the right oil, and temp down, I don't see a problem..... there are alot of gas powered compressors around and use a filter with Hopcalite
Is the right thing to use in that case.

 

[tmassey]

I think if I didn't have the option of making one, I would buy a replacement filter housing for any of the commercially available compressors. This one is only $310:

Ugh, I just knew it would be that one…

The MCH6 cartridge is pretty much universally considered by everyone – except maybe those who actually sell MCH6 compressors – as being too small to be useful. As a duplex cartridge, meaning without CO protection, they last maybe a dozen tanks. As a triplex cartridge, even less.

Even the Bauer P0 filter/coalescer system are uncomfortably small, and they are significantly larger than the MCH6 filter. And much more expensive.

I have been following this thread with interest. But that is my main problem with your project. While a $500 compressor that compresses 3 ft.³ a minute is impressive, it’s far from complete. The big elephant in the room is filtration. And unless you want to make a homemade grenade, you either better know very much what the heck you’re doing before you create your own pressure vessel holding 4500 psi of pressure, or you by a premade one. And I haven’t seen a premade one actually worth owning for less than about $800. Add on other extras like fill whips, a gauge or two to know what’s going on, etc. and you’re approaching $2000.

For something put together out of spare parts and Harbor Freight.

I give you all the props in the world. What are you doing so far looks amazing. But by the time you’re done, I think you’re going to understand exactly why compressors cost what they cost. This reminds me very much of someone who builds a custom roadster, or their own RV camper or some such thing. For a talented builder, they can achieve absolutely amazing results. But if you try to aim for reproducibility (which usually precludes extensive use of found or repurposed materials) and factor in the value of your time (which usually precludes extensive use of hand – manufactured parts), the costs absolutely skyrocket.

But I wish you much success: I hope you prove the naysayers – including me! – wrong. And I will continue to follow with interest.

 

[tmassey]

Where is the CO coming from,?
As long as there is no engine around, and using the right oil, and temp down, I don't see a problem..... there are alot of gas powered compressors around and a filter with Hopcalite
Is the right thing to use in that case.

Thos thread probably isn’t a good place to debate this, but plenty of people have become ill or even died from bad scuba air that was pumped by electric compressors. There have been specific examples where a truck unknowingly idled outside of the intake while the compressor is running.

I have had it myself once, when my wife was mowing the lawn while I was running the compressor. She was dozens of feet away, and the mower wasn’t exactly sitting still underneath the intake. Still has enough carbon monoxide that I was able to detect it with my sensor. I have since added triplex filters and a carbon monoxide sensor on the intake, not just the output.

In addition, lubrication pyrolization is a thing.

Does it happen often? Not at all. The problem is, the consequences are severe: 10 ppm carbon monoxide might not even be noticeable at 1 atm. At 5 atm? now you have a problem.

 

[rjack321]

Read the rest of the post you quoted. I was only talking about the inlet air moisture content, which is what would be removed by an interstage moisture trap. The air isn't even saturated yet between stages because it is coming in pretty dry. It does saturate after the final stage, which goes thorough a separator then this filter:

The fact that you don't realize that air, even at 150psi, is completely saturated is a big red flag for me.

 

[Gone for diving]

Thos thread probably isn’t a good place to debate this, but plenty of people have become ill or even died from bad scuba air that was pumped by electric compressors. There have been specific examples where a truck unknowingly idled outside of the intake while the compressor is running.

I have had it myself once, when my wife was mowing the lawn while I was running the compressor. She was dozens of feet away, and the mower wasn’t exactly sitting still underneath the intake. Still has enough carbon monoxide that I was able to detect it with my sensor. I have since added triplex filters and a carbon monoxide sensor on the intake, not just the output.

In addition, lubrication pyrolization is a thing.

Does it happen often? Not at all. The problem is, the consequences are severe: 10 ppm carbon monoxide might not even be noticeable at 1 atm. At 5 atm? now you have a problem.

So your examples all but one have an engine around and running...

And keeping temps down is important.


If you're running you own compressor anywhere, you need to know what you're doing, and need to pay attention,
that just makes sense,

Ugh, I just knew it would be that one…

The MCH6 cartridge is pretty much universally considered by everyone – except maybe those who actually sell MCH6 compressors – as being too small to be useful. As a duplex cartridge, meaning without CO protection, they last maybe a dozen tanks. As a triplex cartridge, even less.

Even the Bauer P0 filter/coalescer system are uncomfortably small, and they are significantly larger than the MCH6 filter. And much more expensive.

I have been following this thread with interest. But that is my main problem with your project. While a $500 compressor that compresses 3 ft.³ a minute is impressive, it’s far from complete. The big elephant in the room is filtration. And unless you want to make a homemade grenade, you either better know very much what the heck you’re doing before you create your own pressure vessel holding 4500 psi of pressure, or you by a premade one. And I haven’t seen a premade one actually worth owning for less than about $800. Add on other extras like fill whips, a gauge or two to know what’s going on, etc. and you’re approaching $2000.

For something put together out of spare parts and Harbor Freight.

I give you all the props in the world. What are you doing so far looks amazing. But by the time you’re done, I think you’re going to understand exactly why compressors cost what they cost. This reminds me very much of someone who builds a custom roadster, or their own RV camper or some such thing. For a talented builder, they can achieve absolutely amazing results. But if you try to aim for reproducibility (which usually precludes extensive use of found or repurposed materials) and factor in the value of your time (which usually precludes extensive use of hand – manufactured parts), the costs absolutely skyrocket.

But I wish you much success: I hope you prove the naysayers – including me! – wrong. And I will continue to follow with interest.

You can always buy 2 for 620$