# increase flow rate from compressor by using tank ?



## membrane (Jul 10, 2012)

Hey guys,

A newbie here.

I have an air driven motor, which consumes something like 27 cfm at 80 psi. I found an air compressor within my budget which has a max psi rating of 220 psi and a flow rate of 2.5 cfm (at max psi).

Now I'm not sure if that air compressor can deliver the required 27 cfm at 80 psi (2.5 cfm @ 220 psi is the only spec they have). So my question is this, can I put a decent sized tank between my motor and air compressor, and pressurize the tank to a little bit higher than 80 psi, to have the tank act as a buffer and deliver any additional cfm not being able to be delivered by the compressor ?

Thanks


----------



## typoagain (Feb 27, 2012)

Well, yes and no.

I have not figured air usage and stuff like this out for years, but this is I how I remember it_. Hopefully someone who knows more than I do will jump in and correct my errors._

27 cfm is a LOT of air. 27 cfm is about 200 gallons a minute. You could but a large tank in the middle and pump it up to...say 150 psi, and this would supply your needs for a little while. But you're talking about a couple of minutes of continuous use before the tank runs dry. Probably a lot less than 1 minute of use before the tank pressure drops too low-if that long. And I am talking about a 100+ gallon tank. 

That small compressor will run for around 12-15 minutes to pump up the tank enough to get 6 seconds of run time. If your looking at anything near continuous use at 27 cfm, then your looking a big, expensive, two-stage compressor. You're probably looking at a minimum of at least a 7-½-10 hp compressor. I would go with something even larger.

Sorry, but I have to ask what on earth your looking at using that big of an air motor for? 

Just moving that much air will create a lot of noise from the air movement alone. If you try to dump that much air out a ½ inch line you will be able to hear it for at lease a city block away.

Air powered motors are great. You can stall them for long periods of time and they do not get hot, and they are about as tough at they come. But they are an expensive way to generate torque. You can get 2 ½ HP motor and probably do the same job for a lot less money. Heck, even a hydrolic motor is probibply a better choice than an air motor.

_Just remember, all this hot air is worth just what you paid for it. I highly recommend you get another opinion. _


----------



## corey872 (Jan 10, 2010)

Assuming the 'ol 'P1V1 = P2V2' equation would hold relatively true here...pressure1 x volume1 = pressure2 x volume2 so

220psi x 2.5cfm = 80psi x (?)cfm...solve for ?

220x2.5 / 80 = about 6.9cfm at 80 psi

A couple other things would come into play...those are probably max ratings for the air motor, so you may get by with even less pressure/cfm if you are moving something light weight / low friction. 

Your add on tank would help in a surge situation...assuming the air motor runs some / stops some, and the compressor fills a small tank and shuts off in between, then adding a tank would help allow the compressor to store up more air. But if the compressor is already running 100% of the time, adding a tank won't give you anything extra.

As posted, for the cost of a compressor and tank, or likely much cheaper, you could probably get an electric motor to do the same job... assuming you don't need the stall capability and the ability to run in a flammable/hazardous atmosphere like an air motor can.

(probably more hot air from me too!)


----------



## craigsrobotics (Oct 12, 2009)

*don't forget*

don't forget about the duty cycle of the compressor motor...overrun it beyond its duty cycle and you're sure to burn the motor...


----------



## membrane (Jul 10, 2012)

Thanks for the info guys ...

The problem is this air motor is used as a stirrer in a chemical reactor. It will be stirring something 10 times more viscous than honey for something like 24 hrs. So this is why chemists recommended an air motor instead of an e-motor.

I guess then for 24 hrs, as previously said, the tank won't do much. I'll probably look for a beefier air compressor then.

Thanks again


----------



## typoagain (Feb 27, 2012)

membrane said:


> Thanks for the info guys ...
> 
> The problem is this air motor is used as a stirrer in a chemical reactor. It will be stirring something 10 times more viscous than honey for something like 24 hrs. So this is why chemists recommended an air motor instead of an e-motor.
> 
> ...


For something that thick I would think that you might be better off going with large paddles turning at a low RPM. For that I would look to an electric motor and a large reduction belt drive system.

I have also seen large vats stirred with hydraulic motors.

If you plan on using this much try to keep operating cost in mind. 

I know a guy who wanted a HUGE overhead crane. So he bought a building with one already in it. 

What he never considered is that the electrical draw was so high that it placed a big demand on his meter. Due to the demand, just firing up the crane once a month drove his electric cost up over $300 a month.

It sounds like an interesting project. Let us know how it comes out.


----------



## corey872 (Jan 10, 2010)

'brane - WOW - this sounds like a 'real project' not just some cobbled together creature for a few scares! Sounds interesting...care to share details? ...or if it's secret, I understand, too!

Yes for a 24 hour continuous run, a tank won't get you anything additional. It would only help for off/on cycles.

The chemists who told you this - are they working in big industrial complexes? Most likely that is what spurred the use of an air motor as most industries have HUGE air compressors and compressed air systems, so 27 CFM is virtually nothing and running 24/7 is nothing.

For a home/garage/shop environment, that is a pretty big compressor and a long run. The catch is, while compressed air has it's uses it's terribly lossy to transfer power. I have a fairly large "6.5hp" compressor, 60 gallon tank, ~12cfm, and it's about all it can do to keep up with a decent sized air grinder. I have a 1/2hp electric grinder which will go all day and outperform the air grinder by a fair amount. 

If this process is flammable, gives off explosive vapors, etc - then an air motor is definitely the way to go. But if that is not needed, a properly sized, rated, and geared electric motor would still work just as well. If the motor is rated for continuous duty and running within it's rated operating parameters, then it doesn't care what it's doing...directly stirring chemicals...or running an air compressor to compress air to run an air motor to stir chemicals.  

As typo says, you'd probably need a gear reduction, but as long as that is sized to keep the motor at rated rpm/hp, you should be fine.


----------



## membrane (Jul 10, 2012)

I'll share .. No secret 

Basically, I'm synthesizing a polymer from scratch, and the mixture is highly acidic and highly viscous at room temperature (like 5000 Pa-s; which is 1000 times more viscous than honey). So to bring the viscosity down to something 'sane', like 100 Pa-s, temperature needs to go up to 200 C. This is near the flash-point of the mixture.

So those chemists recommended I use an air motor as a safety precaution. And yes they are used to industrial scale air compressors.

Now, the building this setup will be in has compressed air pipes, and my lab does have compressed air outlets. I know those are all connected to a main compressor (or maybe more than one), except I didn't check the ratings yet. Once I do, I'll ask you guys for an optimal setup. Cuz I don't want my motor to stop spinning when someone else in the building decides to use 'share' the compressor with me.


----------

