Air Compressor Question

More accurately, this is an air compressorS question.

Anyone using more than one air compressor working on a single air system?

Sandblasters, die grinders and such have pretty hefty demands for air.

I have a 17 gallon Craftsman that can make about 6.5 CFM at 90 psi, but struggles with the sandblaster running. Sandblasting cabinet requires "5 to 15 CFM." Seems like a large range, but in any case, a friend donated me a second air compressor. It's an old 2 cylinder thing, around 15 gallons, that has a 1-1/2 horsepower 4 pole motor on it. (No CFM specs anywhere to be found.)

What are the rules for working them together? Do I need check valves? I am entertaining the idea adding some additional air storage in the form of a recently expired 100 lb propane tank. That would give me around 60 gallons of tank + any lines.

Dan

 

don't use a propane tank the particular laws in Canada regarding modifying air storage tanks or making one without certification in place are very short. In case of accident you have one option "Plead Guilty" opening up all sorts of lawsuits for anyone that may get injured from a failure. Oh and household insurance will find a way of not paying out any claims so you would be on the hook for the full amount.

Air compressors in parallel will need valves to dump pressure right before a manifold also backflow prevents so as not to place any extra strain on the compressor during start up.

 

http://www.servicenl.gov.nl.ca/safety/bulletins/sb_pressure_vessels.pdf

 

well that was fast. usually takes me a couple of minutes to find those documents.

 

Hi John,

What is the reason for the valves?

My thinking is the two compressor tanks are plumbed together and act as one tank. Either the pressure in that combined tank is low and the compressors start up or it is enough to open their respective switches and they shut off. No compressor should see any pressure higher than the highest of the two pressure switches dictate. It's unlikely that they will start at exactly the same.

There aren't many clear answers on the web about this.

Dan

 

You want the pressure to be dumped after it shuts off. This reduces the stress on the compressor during startup and If memory serves you do not want to be back feeding a compressor either.

 

I found this video that makes some sense of it. (until the guy hooks up the extra 7 hoses! LOL)


This is effectively what I want to do.

 

the key to what he was doing is having matched compressors and for the limited use probably never find the need for pressure dumps. They are on the compressor separating the piston from the tank typically so you may actually have them and they make that little pfft sound when the compressor shuts off.
Or you may not have them, if you are not running them 8-12 hours a day you may never notice any problem. If the breaker kicks off during start-up then that is from the extra load of having the compressor exhaust above atmospheric pressure and loading up the motor

 

His point of common coupling is before the regulators. If you couple them after their respective regulators, the a check valves should be used. This prevents damaging the regulators with back pressure.

Got it.

Thanks,

Dan

 

That makes sense, it has been a few decades since I played with pneumatics.

 

I'll do some experimenting...with full body armour of course. LOL
I'll post what I have learned.

Dan

 

I have both my old compressors running in tandem.

The one on the left is a 1.5 horsepower (mystery CFM) with a 14.5 gallon tank.
The one on the right is a 1.0 horsepower twin cylinder 6.5 CFM@90 psi and 17 gallon tank.
Pressure switches are both set to 120 psi. From the tanks I run through ball valves and into the 5 port manifold.
If I just want the extra capacity, I can switch one compressor off and let the one that's running fill both tanks.
Also, on the manifold, I have extra ports for adding another additional tanks.

I can run the die grinder or sand blaster continuously with this setup. Mission accomplished.

Dan

 

I was contemplating going down to the store and dropping $800 on an 11.5 CFM, then the washing machine crapped (ka-ching) out, was needing new tires (ka-ching) etc. So I reckoned I could improvise something. I had the one compressor for years and looked after it. I swapped a kitchen knife for the other. With a bunch of plumbing they work like a single unit with the CFM and extra storage that comes in handy. Maybe when I sell a few more knifes I can get a new one and put those compressor motors to use. Hmmmm.

Dan