I really hate top posting. sci.physics dropped from the
list. This is a simple wrencher's problem. send me email
if necessary as I don't read the other groups. My answers
are interspersed in the text.

Grant Erwin wrote:

Alan Horowitz wrote:

Pardon the fairly wide net of groups I'm posting to; I'm trying to
catch the guy who knows how to answer this question.....

Harbor Freight has a 5-gallon, 125-PS air tank that is small enough
to be hauled around inside a rolling peice of luggage, which is how I
would do it in my field-service type of work.

Can that amount of air, run a impact wrench long enough to crack a
tough-dog nut to the point where a normal long-handled hand wrench
would handle it? My experience is that I can do it by hand once it's
down to 70 foot-pounds of torque. Depending upon how badly placed the
thing is inside a crowded cabinet, above/below my arm level, etc. But
let's use 70.

Given an air tank rated in X gallons @ Y PSI, how do I calculate the
time it would deliver air at Z psi to an impact wrench at a
consumption rate of Q cfm, where Z is smaller than Y? And how much
power is that, in terms of (let us say) watthours?

You don't need to go through all this exercise when all you want
is high torque long enough to break free a difficult nut. It
is only torque you need, not "work."

Buy a really good electric impact and forget air. After
all, you can always put a pipe wrench on the extension
to give the power tool a boost if needed. That's been my
solution to "need more torque" since I was a kid with
worn out impact tools. A 3/4 impact driver, now there's
a man's tool. If air you won't run that very long off a 5
gallon tank.

Don't forget, air pressure in a small tank with an
undersized compressor drops rapidly as does the torque
it produces. An air impact will maintain torque running
continuously all day, till you plain wear it out.

Who sells a flexible drive that is (say) five feet long, and can
handle the torque required to bust open a rusted nut, if the
emplacement is such that I can't get a power tool directly onto the
socket?

You cannot direct the torque 100% in a flexible drive
5 feet long.

If this is for your work, Alan, I suggest you invest in buying
one of the small tanks and trying it out. Time is money ..

If he is on the clock already, time is money in his
pocket.