I have a low-end Harbor Freight 8 gallon air compressor that has many
times over earned its $100 cost.

However, there are times when I would like to have a larger air supply
tank such as when I am blowing out my irrigation system. Of course the
steady-state is limited by the compressor motor to about 4-5 CFM@90 psi.

But I was wondering whether I could extend at least the initial volume
by adding an additional tank.

Harbor Freight for example sells an 11 gallon portable air tank
(http://www.harborfreight.com/11-gall...ank-65595.html)
for about $38. It is rated up to 125 psi (same as my compressor) and
comes with a gauge and a tire-type fitting.

I was thinking that I could re-plumb to NPT and attach it to the drain
hole on my compressor tank (with a T-fitting and ball valve to still
allow drainage).

This would then give me effectively 19 gallons of initial air supply.

Of course, I would need to be careful about duty cycle since filling up
19 gallons vs. 8 gallons would be like doing 2 1/2 continuous fills of
my original tank.

But assuming that I am careful about duty cycle is this a reasonable way
to temporarily extend the initial air supply for occassional uses where
I need to get the advantages of a larger tank?

(Note that it seems that several of the Harbor Freight compressors use
the same HP motor with similar CFM ratings for a range of tank sizes --
probably because the HP is ultimately limited by the 110V 15A supply
circuit)

Thanks!