My diy air compressor aftercooler

[BackYard_Mechanic]

I've been reading through and using these forums for years so this is my first post showing what I did with an old air compressor that sat in a shed for 25 years and was mounted to a peice of wood when I found it. I had also been experimenting with ways to dry my air for painting purposes and after seeing people using transmission coolers as an aftercooler I thought I might beable to use an old heat register for the same purposes on my build. I had an oiless compressor that had a 22 gallon tank and It was the perfect size. after welding a larger base to accommodate the much larger reciprocating pump I cleaned and then cut up the heat register pipe in 1 foot sections and silver soldered it together. After determining that I could not mount the cooler in front of the pulley as originally planned without a serious headache I decided to mount it directly to the tank base behind the pump. I attached the pump outlet to the top of the cooler with various fittings. The bottom I plumped to a water trap/ filter and from there used 1/2" copper tubing to connect it to the check valve leading into the tank. Its working very well as is but I do plan on adding a guard for the cooler along with a muffin fan wired to the pressure switch for extra efficiency. As is the outlet stays cool to the touch while the inlet to to the cooler is almost to hot to touch after running just a few min

 

[BackYard_Mechanic]

Sorry about the lack of photos throughout the build I had some trouble uploading my photos and this was my very first post ever. I will be posting photos when I get the muffin fan a gaurd finished. Anyone looking to make one themselves make sure that you use fittings and pipe as big as or larger than the original pump discharge tube and be sure that water cannot collect or return to the pump as that would be bad.. gravity is your friend on this project. Also I used silver solder because the air pressures are rather high and the temps can get upwards of 300 f so I wasn't sure if regular solder would be up to the job.. i did have one leak I found on the first test and had to remove that part of the pipe clean up and completely start over to ensure a nice seal. Just an FYI the cooler pipe diameter is 3/4" so its large

 

[metlmunchr]

I've mentioned this before, but it's worth saying again. The finned copper tube as used in hot water baseboard (what the OP is using) will shed 6X as much heat per foot of length as bare copper tubing. The OP's 4 ft of finned tube is equivalent to 24ft of bare 3/4" copper.

One suggestion from my own experience. Any reciprocating compressor will transfer a lot of vibration to the discharge piping. Over time, it will cause the copper tubing to crack. If you add a hose between the pump and your aftercooler it will isolate the vibration.

I've got a 10hp 2 stage compressor in my shop where I make a living. From the factory, the line from the compressor to the tank was a length of 1" soft copper. It was fine for a couple years and then it cracked. I removed it, patched the crack with silfos, and replaced it. After that, it would crack again in another place roughly every 6 months. Eventually I replaced it with a hydraulic hose and it's been trouble free for over 10 years.

 

[BackYard_Mechanic]

Thanks for the input.. I thought about the vibration but was worried the extreme heat coming out of the head would be to much for anything besides metal.. i may mount some rubber vibration pads under the cooler mounts like I already have underneath the pump if it becomes an issue.. also a side note If u noticed the pipe end cap sticking out beneath the cooler that was my solution to access to the oil drain from the pump as it was hard to get to with everything being in the way.. a 3" length of 1/4" black pipe works nicely

 

[Kaizen]

I've mentioned this before, but it's worth saying again. The finned copper tube as used in hot water baseboard (what the OP is using) will shed 6X as much heat per foot of length as bare copper tubing. The OP's 4 ft of finned tube is equivalent to 24ft of bare 3/4" copper.

One suggestion from my own experience. Any reciprocating compressor will transfer a lot of vibration to the discharge piping. Over time, it will cause the copper tubing to crack. If you add a hose between the pump and your aftercooler it will isolate the vibration.

I've got a 10hp 2 stage compressor in my shop where I make a living. From the factory, the line from the compressor to the tank was a length of 1" soft copper. It was fine for a couple years and then it cracked. I removed it, patched the crack with silfos, and replaced it. After that, it would crack again in another place roughly every 6 months. Eventually I replaced it with a hydraulic hose and it's been trouble free for over 10 years.

Can you find psi rating for baseboard? I didn’t see anything in slantfin site. It has a thin wall and usually runs at 30psi. That’s a Lot different then 150 psi


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[The Cobbler]

pretty sure fin tube is thinner wall than type m copper and not rated for even potable water pressure, never mind 125 psi plus air.

 

[metlmunchr]

Slant Fin rates theirs at a max safe working pressure of 202 psi @ 250°F.

I just miked the wall thickness of a new length of fin tube baseboard stored in my garage. The wall thickness is .025".

M hard copper wall is .032". Working pressure is 680 psi @ 150°F. This gives a hoop stress of 8236 psi.

L hard copper wall is .045" . Working pressure is 972 psi @ 150°F. This gives a hoop stress of 8478 psi.

Calculating pressure for the .025" wall tube using a hoop stress of 8000 psi gives a working pressure of 485 psi.

Slant Fin is likely derating their max pressure to make for a greater than standard safety factor for the 250°F temperature rating point since a failure carrying water @ 250°F would result in the water instantly flashing to steam which is a much more dangerous situation than a simple hot water leak.

In either case of working pressure, the finned tube the OP is using has more than adequate pressure capability for normal compressed air pressures.

Working pressures for 3/4" type L and M hard copper are from engineeringtoolbox.com Same source also has burst pressures for both types of tubing and these pressures are in the several thousand psi range.

 

[Kaizen]

Slant Fin rates theirs at a max safe working pressure of 202 psi @ 250°F.

I just miked the wall thickness of a new length of fin tube baseboard stored in my garage. The wall thickness is .025".

M hard copper wall is .032". Working pressure is 680 psi @ 150°F. This gives a hoop stress of 8236 psi.

L hard copper wall is .045" . Working pressure is 972 psi @ 150°F. This gives a hoop stress of 8478 psi.

Calculating pressure for the .025" wall tube using a hoop stress of 8000 psi gives a working pressure of 485 psi.

Slant Fin is likely derating their max pressure to make for a greater than standard safety factor for the 250°F temperature rating point since a failure carrying water @ 250°F would result in the water instantly flashing to steam which is a much more dangerous situation than a simple hot water leak.

In either case of working pressure, the finned tube the OP is using has more than adequate pressure capability for normal compressed air pressures.

Working pressures for 3/4" type L and M hard copper are from engineeringtoolbox.com Same source also has burst pressures for both types of tubing and these pressures are in the several thousand psi range.

Thanks for the detailed analysis


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[BackYard_Mechanic]

This stuff is very heavy duty and was about as thick as the elbows and such that I soldered to it.. its atleast type L copper tubing thickness wise which my entire air system is plumbed with atleast 40 ft of it is also from a very old house so maybey newer style is thinner all I know is that I have no doubts about this holding pressure and it does go to a check valve so Its not staying at pressure due to relief valve..nor is it even 150 since my compressor only goes to 125 psi. Has worked well after hours of using high cfm tools so far.

 

[Kaizen]

This stuff is very heavy duty and was about as thick as the elbows and such that I soldered to it.. its atleast type L copper tubing thickness wise which my entire air system is plumbed with atleast 40 ft of it is also from a very old house so maybey newer style is thinner all I know is that I have no doubts about this holding pressure and it does go to a check valve so Its not staying at pressure due to relief valve..nor is it even 150 since my compressor only goes to 125 psi. Has worked well after hours of using high cfm tools so far.

I have 20 feet of used baseboard that I was going to use as part of a precooler. Had visions of a burst and one of those aluminum squares flying. Mine is thin wall so think I will use it behind a wall just in case.


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[The Cobbler]

Slant Fin rates theirs at a max safe working pressure o....

good to know, thanks for posting

 

[bradpac]

Hmm, baseboard heaters...don't think I've ever seen one in person. Great build though, a cooler is definitely in the plans for my 5hp once I get a working garage again.

 

[Iron Beaver]

I like this idea. I might have to steal it some day to dry air for my plasma cutter

 

[chrispyny]

I should take pics of my cooler i made for my sand blaster. It’s a run from the compressor, across my garage, and into a water seperator, and regulator. 22’ of slant fin tube from a piece i cut out of my house while remodeling. 3/4” pipe. Because sand blasters are air hogs, by the time air reaches my sand blaster, the air is cool, and water condenses in the separator quickly. It leaves my cyclone blaster clog free and working 100% all the time.