On 2009-03-10, rigger wrote:
Think of your air system as a battery. When it pumps up to (a charge)
of 160# and turns off nothing is lost.

Rigger, this is untrue and Richard Kinch is correct within his set of
assumptions (which probably do not apply to your home shop).

If you use a given amount of energy (such as 1 kilowatt-hour) to
compress air to 120 PSI, you can then use that air to power your air
tools and get back some good fraction of that energy.

If you use the same 1 kilowatt-hour to compress air to higher
pressure, such as 175 PSI, you will get less energy out of your tools.

This is because compressing air to higher pressure heats air more than
compressing air to lower pressure, and that heat is completely wasted
(unless you are also heating your shop in winter, for example).

So it is indeed true that compressing air to more than the required
pressure wastes energy. And it is partly a reason for rotary screw
compressors.

However, many "home shop" owners do not particularly care about the
cost of energy, as they use their compressors very little, say an hour
per week. A more important issue for them could be availability of a
lot of air for short bursts of air use. And under these circumstances,
maintaining a higher pressure makes sense.

When you use part of the charge for air motors, etc. you only use
the portion going through your device. Nothing is lost.

Energy is lost when compressing and heating.

i

Perhaps you're thinking of a system that pumps to a reservior past
a pressure relief valve to a hydraulic tank; an air system doesn't
work this way.

dennis
in nca

--
Due to extreme spam originating from Google Groups, and their inattention
to spammers, I and many others block all articles originating
from Google Groups. If you want your postings to be seen by
more readers you will need to find a different means of
posting on Usenet.
http://improve-usenet.org/