# CFM - pump or tank size?



## johnnyv49 (Nov 4, 2014)

Hello all,

I have a small shop and am looking at another compressor. I don't have a 220 line in there and being I'm building a new shop in my garage it doesn't make sense to run it to this shop. 

the compressor I have currently is just not cutting it. I'm looking at a 6hp 29gal (oil) compressor. 5.9 CFM @ 90 PSI, 7.3 CFM @ 40 PSI

I have a large tank in my shop. If I join the two tanks together will that get me by? What would the second tank do?

Probably the largest things I will use is a cup gun for spraying fiberglass and some auto-body air tools.


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## OldMasterTech (Jul 25, 2014)

6 HP at 115vac would draw over 60 amps, do you have #6 CU wire and adequate service for this application?

The extra storage capacity tends to give less dramatic pressure drops/rise while working. One of my systems has 3 100 gal tanks and 800' of 1" copper tubing and two compressors each delivering 100 cfm - very stable pressure there!


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## Osviur (Sep 7, 2015)

*Compressor*

Hello Johnnyv49,

I think that there must be a mistake in the numbers that you mention about the 6 HP compressor or I am not understanding your explanation ( sorry for the latter): A 6 HP comp. will deliver at least 15 CFM at 90 PSI, in a single stage pump configuration, normally may be in the 18 - 20 CFM range. With this displacement, the 29 gal. tank will be filled in a very few minutes and discharged three or four times longer using your shop tools continuosly, not normal. Adding a second, larger tank, the compressor will wok for more extended periods, reducing the frequent starts, when the motor takes , during some seconds, up to six times the nominal current, overloading the power lines inside your shop. Not good.

With the extra tank the air discharge will last longer, with less noise and power consumption. If you still have not bought the new compressor, I would advice you to adquire a two stage one, working at 175 PSI and in this way gain in afficiency and air capacity. The same tank working at 175 PSI will contain 150% mor air than at 120 PSI (aprox) .


Regards


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