On Wed, 4 May 1994, Olin Kane wrote:
> Scott Fisher sez -
>
> > - 75 feet of hose and 50 feet of extension cord work just great,
> > allowing you to get anywhere you want, and for those of us with
> This 50 extension cord better be pretty hairy to handle a 4 hp motor. A
> regular cord will not handle the current (cord will get hot, motor will
> run slow and eventually a fuse or breaker will blow). Be sure to get use
> a very heavy duty cord such as those used by commercial contractors.
>
> If you have the choice of buying an extension cord or an extension hose,
> buy the cord. You lose pressure at the end of a long air hose vs whats
> available at the tank.
>
I agree with Olin about the need to use a very heavy duty extension cord,
but I don't agree with his final paragraph. If it is a choice between an
extension cord and and extension hose, I would recommend the hose. You
can compensate for pressure drop in the air hose by increasing the
pressure at the inlet, but you cannot compensate for voltage drop along
the extension cord, which is bad for the motor. Incidentally, the 3/8
inch hose that commonly is sold is on the small side--get a larger size
because the resistance of the hose is proportional to the inverse of the
fourth power of the radius. A hose with a 1/2" internal diameter has less
than 1/3 the resistance of 3/8" hose.
Where the exact pressure is critical, as it is for finish coat spraying,
you should have a pressure gauge on the spray gun inlet, in which case the
pressure drop in the hose is not especially important--just adjust the
pressure until you have the correct pressure with the tool operating. The
pressure on the tank is never an accurate measure of the pressure at the
tool, because there is pressure drop in any hose of practical diameter.
Ray Gibbons Dept. of Molecular Physiology & Biophysics
Univ. of Vermont College of Medicine, Burlington, VT
gibbons@northpole.med.uvm.edu (802) 656-8910
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