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Air compressors in series?
Air compressors in series?
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Old 17th August 2018, 02:38 AM   #21
Andrew Eckhardt is offline Andrew Eckhardt  United States
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This probably won't help but I used to know a guy with an auto shop that ran a small block Chevy V8 on four cylinders and used the other bank as an air compressor. I've never seen a bigger air compressor.
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Old 17th August 2018, 05:03 AM   #22
1audio is offline 1audio  United States
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Air compressors in series?
I just checked and a 5HP compressor (premium industrial grade) should be able to provide 15 CFM continuously. A cheap "gas station" grade more like 10 CFM. The 3 to 1 price difference does get you more value and probably many more years of service if you do run it at full throttle. If you empty your tank that fast (4 cf or 30 gal. is not that big, most compressors here for industrial use have 60-80 gallon tanks (sorry for the ongoing dimension conversion stuff. I live in a backwards country and don't use international units enough to know them) then something is not quite right. I found this which was really illuminating: https://mastertoolrepair.com/images/...CFM_Output.pdf
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Old 17th August 2018, 06:03 AM   #23
PRR is offline PRR  United States
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Quote:
Originally Posted by Andrew Eckhardt View Post
...I've never seen a bigger air compressor.
They are not found in nice neighborhoods.

A LOT of the money made in the African diamond district was actually made by the air compression companies. Hopefuls would rent jackhammers and buy air from extremely long pipes, and dig until they hit diamonds (or went broke). Hundreds of jackhammers in one area use a LOT of air.

Old books/mags----
Compressed Air: Its Production Uses, and Applications {1909}
Compressed Air, 1901

Current examples---
Large Compressor Packages Project Case Studies
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Old 18th August 2018, 03:40 AM   #24
Dave Zan is offline Dave Zan  Australia
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Quote:
Originally Posted by 1audio View Post
...If you empty your tank that fast...
I don't empty the tank that fast, that's the time before the pressure drops to the point that the compressor should kick in.
My calculation is exactly the same as the link you provided, so no mistake.
The point was that an increase in tank size makes little difference, a move to 60 gallon (AKA 8 cubic feet) adds only another 15 seconds before the compressor needs to start.

Quote:
I live in a backwards country and don't use international units...
I am OK with cubic feet and CFM, but why is it then customary to quote the tank volume in gallons?
I did a triathlon in the USA with the 1500 yard swim, a 25 mile cycle and a 10 km run.
MAKE YOUR MIND UP!

Best wishes
David
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Old 18th August 2018, 05:13 AM   #25
suzyj is offline suzyj  Australia
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Quote:
Originally Posted by Dave Zan View Post
I already have a tank 1.2 m wide, this is not a small portable compressor, it's a fixed, fairly heavy duty professional unit that holds about 4 cubic feet.
A 1 atmosphere drop is about the limit before the blaster becomes unacceptably inefficient, so at 16 CFM that happens in only 15 seconds or so.
What work have you done where this is a "significant portion of the job"?
I wish my jobs were so short, I've never even seen a job like that.
Sand blast work always seems to require sustained full output, it's not like some little touch-up spray job where you hit it for a few seconds, check the finish, think about the next pass...
So I don't think more receiver volume is a useful option.

Best wishes
David
The air compressor that I have connected to a sand blasting cabinet is reasonably large, about 20-30CFM with a ~300l receiver.

Most of the components that we blast are reasonably small, and there's maybe 60-90 seconds of blasting, then a couple of minutes of stuffing about. That's where the thought of just going to a bigger receiver comes from.

One option for the odd bigger job is renting. We have a trailer mounted diesel compressor that we primarily use for running air hoists that would be perfect for sand blasting - probably 30-40cfm. I'm sure the hire places have similar units.
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Old 18th August 2018, 08:35 PM   #26
daqvin_carter is offline daqvin_carter  United States
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All of this talk of PSI, BARS, CFM, KM, Miles reminds me of a slightly amusing (or disappointing) meeting I had at work years ago.
My company made computer controlled routers that cut circuit boards out of panels with a small cutting bit rotating about 30,000 RPM. The bearings in the spindles had a limited life and required replacement from time to time.
We were just assigned a new President who barely earned a Biology degree in college. I really thing that degree was a struggle to get for him. He just had good family support it seems.

Anyway, we were testing a new air bearing spindle that would not require replacement unless you crashed the bit into something hard. All went well with testing and we had a design meeting to see if we should use this new spindle on our new machine.

One person brought up one requirement that could be a problem for some places. Most of the machines on site require air so clients are sure to have about 80 PSI of air though this air bearing spindle used about 2.5 CFM at 80 pounds which would be more than what many sites could provide.

Dear president hears the 2.5 CFM argument and immediately asks how much is that in bars? The bravest people in the room tried to explain the difference between air pressure and air volume using little words that would not offend the president. This went on for maybe 30 minutes annoying everyone in the room. I do not think dear president reached any understanding and we were able to exit the meeting eventually.

We eventually did lose dear president after key employee departures.
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Old 18th August 2018, 09:01 PM   #27
multisync is online now multisync  Canada
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Equipment that I used to work on had 2 compressors. Most of the functions were handled by one compressor. When additional functions were required a second compressor would start up to provide additional air volume. The outputs of both were connected together with check valves. There were 2 tanks and 2 pressure regulators.

Each compressor could do about 50-60PSI before stalling. A buddy of mine took home a marginal compressor and hooked it up to 2-40gallon hot water tanks (no longer used for hot water). No they didnt blow up. He would run the compressor for a few hours, then he would use the "air tanks" to pump up his tractor tires.

Maybe all you need are very large air tanks and a regulator
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Old 18th August 2018, 09:03 PM   #28
PRR is offline PRR  United States
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> Dear president hears the 2.5 CFM argument and immediately asks how much is that in bars?

In terms of animals: CFM is how fast the elephant makes a puddle. PSI/Bar is how far he can throw his pee.

A dog may throw his pee pretty far. But he can never make enough pee per minute to cool a hot bearing.

Yes, I have known top-bosses of similar education who still would not get it.
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Old 18th August 2018, 09:12 PM   #29
PRR is offline PRR  United States
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Quote:
Originally Posted by Dave Zan View Post
... ... why is it then customary to quote the tank volume in gallons?...
Yeah!!

Propane is sold by the gallon. Which has to be corrected for temperature.

Propane tanks are rated by the weight of water they could hold. Not gallons, a traditional water-measure (and what you see on air-tanks), but weight.

I guess this makes it easier for the tank-maker. A scale will count pounds much easier than pouring measuring-cups of water. Though ideally it still needs temp-correction.
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Old 31st August 2018, 06:06 AM   #30
Wot is offline Wot  Australia
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The easiest way to increase your compressor volume is to hook up a pair of 45kilo gas bottles which can be had for very little or free at the local tip. Then you only have to buy the fitting with the left hand thread to connect them. The big benefit is they form a condensation trap and you end up with nice dry air at the end.
It's good to fit a drain **** on the first one after the compressor as this will eliminate moisture by the time it gets into the second one.
Having one fully pumped up you can inflate a car or tractor tyre out in the paddock with no extra power. A couple of pieces of angle iron welded on the sides will allow them to be strapped on the back of the ute without rolling around.
I'm not sure what the pressure limits are on those bottles but it's well over 100psi as long as they aren't rusted out of course.
But for continuous use you're still going to need a bigger compressor.
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