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Tool Talk Discussion Forum

Dual air compressors - would it work?

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Mattlt

05-17-2005 05:50:14




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Had a wild hair. Would it work to connect two small air compressors together? Would they "fight" each other? Would it double the SCFM, or are there other factors to consider?

What about the cutin / cutout pressure switches? Would they need to be set slightly different so as not to cut in/out at the same time? Maybe one pressure switch could be used with both compressors?

Lots of questions. Just happened to think about it. Figured you guys would have opinions.

Thanks.

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Big Jim

05-18-2005 21:07:37




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 Re: Dual air compressors - would it work? in reply to Mattlt, 05-17-2005 05:50:14  
Only caution is that they should be the same type of compressors - all single stage or all 2 stage. I worked in a shop that had 6 assorted 2-stage units all hooked to the same manifold.



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jeffcat

05-18-2005 10:12:23




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 Re: Dual air compressors - would it work? in reply to Mattlt, 05-17-2005 05:50:14  
Sure you can. In my basemant I have a small 2.5hp China unit from Pep Boys and a nice Emglo K15-8P unit hooked to the same lines. Also have three old Freon tanks in line to provide more volume. This set up allows me to use my little hand sand blaster out in the yard with no problems. The Emglo kicks on first and then the other. The Emglo also has the unloader heads and will "coast" at 120lbs. All of it works great. Jeffcat

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Mark - IN.

05-17-2005 14:51:13




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 Re: Dual air compressors - would it work? in reply to Mattlt, 05-17-2005 05:50:14  
Once had one, manufactured that way from some place in Ohio. It was a 100 gallon tank with two compressor heads driven by two seperate 1 HP 208 3 phase motors. I got it for free after making a joke that it'd be nice to have without really looking at it. Then the guy kept after me to come pick it up for months, until I finally did and realized that it took four guys to lift and took up the entire pickup bed. Nonetheless, I took it home, mounted it on dollies, but never took the time to rewire or replace the motors for 220 single phase, and gave it away. Now I wish I had it.

Can it be done? Absolutely. Can't remember the manufacturer, but was out of Ohio, was big and blue (industrial), had a dryer for moisture between the heads, and think began with the letter "L".

Good luck, Mark

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captaink

05-17-2005 10:44:05




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 Re: Dual air compressors - would it work? in reply to Mattlt, 05-17-2005 05:50:14  
Well, I might as well chip in here. I have two, one on each end of my shop. One is a three horse (about 25 years old) the other a 7.5 horse (less than a year old). Both are two cylinder single stage compressors. The big one has a 60 gallon tank on it; the other has no tank and pumps directly into the air line in my shop. Both are connected to the air line in my shop. The small one kicks in first, the big one five pounds lower and also cuts out at 5 lbs higher. I have two 100# propane bottles (I was using them for a pressure tank for the smaller one when it rusted through) that I can add by opening a valve. I have them wired on two different 240 volt circuits and two different pressure switches. I love it! Under low CFM demand (filling tires etc) the old three horse can keep up, but when I have high CFM loads (two or more of us working with air tools) I can open up a bunch of air storage, and both compressors will be running to provide lots of air flow.

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Bus Driver

05-17-2005 10:08:36




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 Re: Dual air compressors - would it work? in reply to Mattlt, 05-17-2005 05:50:14  
More than 50 years ago, I had two identical belt-driven refirgeration compressors. My selection of motors included one 1/3 Hp capacitor start and two 1/6 HP capacitor start. So one compressor is driven by the 1/3 HP and the other compressor is driven by the two 1/6 HP belted together- Two compressors, three motors, into one tank, no check valves. The pressure switch is double pole, fed by 120/240. The 1/3 motor is fed from one pole of the switch, the two 1/6 from the other pole. They all start and stop at the same time. Feeding 80 galon tank at 100 PSI maximum. Air volume delivery is low, but it fitted the budget at the time. All components but the tank came for the junk pile. Great for tires and shop work, but not sand blasting nor painting. I do not live there now but the air outfit still works.

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Bryan in Iowa

05-17-2005 07:13:33




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 Re: Dual air compressors - would it work? in reply to Mattlt, 05-17-2005 05:50:14  
I have 2 compressors in my shop . Both feeding all plumbed air lines . One compressor kicks on at lower psi than the other .Mostly run the one , but when air demand is high , 2nd compressor kicks in . Work great when couples guys using air tools at same time , or sand blasting . But more and more these days using battery powered impacts .



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buickanddeere

05-17-2005 07:09:56




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 Re: Dual air compressors - would it work? in reply to Mattlt, 05-17-2005 05:50:14  
It's done all the time. The pump(s) already has a check valve to keep air from flowing back from the tank. Usually in industry three 50% capacity compressors are used. One is on standby. The other two alternate,taking turns. If demand requires, the 2nd pump starts. You DO NOT want both pumps to start at the same time. The typical wiring to compressor motors is too long and too light a gauge. Starting both together is just going to drag the voltage to brownout & burnout levels. That is if they will even start at all due to low torque from low voltage.

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sawtooth

05-17-2005 18:41:01




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 Re: Dual air compressors - would it work? in reply to buickanddeere, 05-17-2005 07:09:56  
A factory where I used to work had four 800 h.p. compressors. Like you said, one would usually be on standby (down for maintenance), but 3 were often running at the same time, feeding the same lines.



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buickanddeere

05-18-2005 08:43:09




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 Re: Dual air compressors - would it work? in reply to sawtooth, 05-17-2005 18:41:01  
Biggest piston compressors I've seen were 200HP V twin two stage oil-less units with unloaders for low pressure instrument air. Dry carbon piston rings and isolation form the crankcase to ensure no oil in the air. They have a sound all of thier own. 12 of these compressors sitting in a row. Then there are the HP instrumnet compressors, service air compressor and breathing air compressors.And a bank of four compressors making 4500psi for the switchyard airblast breakers.

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Coliron

05-17-2005 07:09:19




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 Re: Dual air compressors - would it work? in reply to Mattlt, 05-17-2005 05:50:14  
Matt, Retired from an Aircraft mfg in Seattle area a few yrs ago. They had huge compressors in a battery that had lead, lag capabilites. The lead, lag system was changeable to make any comp the lead and each other comp could be made to come on line in order of set up. Like old said in the previous post, there were check or non-return valves in the system. Failure of the check valves would cause problems. You could have as many as 5 comps running flat out on all four stages with the 6th comp floating its four stages to control the air press. There would be times when several of them would be idling along during low demand of the supply which varied greatly all day. You could probably do it by setting one comp at the high end of your press range and the second comp at the low end of your range. It would help to have a receiving tank to keep the two comps from cycling at a rapid pace. On the discharge form the receiver you could have a pressure reducing valve that would maintain the line press as a constant. If it doesn`t work you can always try something else. The CFM of the two comps would add up. System flow would be affected by line size as well as hose size. You can only flow X amount of air through a certain size line at a given pressure.

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Chad Franke

05-17-2005 06:50:44




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 Re: Dual air compressors - would it work? in reply to Mattlt, 05-17-2005 05:50:14  
It could work, you would need to wire them so they both use 1 pressure switch (turn both on/off at same time). I don't know, but I would think it would work best if they were pretty well matched (SCFM).

If they each had a separate switch, one set lower, the lower one would almost never run, you would have to dump the pressure from the higher low setting to the lower low setting before the first compressor could stop the pressure drop...

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old

05-17-2005 05:57:33




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 Re: Dual air compressors - would it work? in reply to Mattlt, 05-17-2005 05:50:14  
It might work but I think you would need check valves in each compressor line before the tank, That way one could not back feed on the other.



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