"Tom Gardner" wrote in message
et...
My air supply is in stages. One 7.5 hp 3-phase 230v Quincy can usually
carry the load. It come on at 90 and runs to 120, or there about. If the
demand is bigger, another Quincy gets put on line. I also have a 10 hp.
Hydrovane as a back-up. I have yet another Quincy in reserve. I hate not
having air! We're looking at #1 that seems to be about 50% duty cycle
with just less than 1 minute off time One of my ideas was for the lowest mechanic to catalog every air leak and
repair them...they add up quick. It seems we can go about a year before
they become an issue.


We had a 25 hp Quincy where I used to work. When we were doing a
system blowdown, it could barely keep up as long as we kept the
blowdown pressure under 40 psig. During a normal process run, it would
cycle at about 45 second intervals. In talking with our
service company, anything that cycles more than 15-20 times an hour
needs to run in unloader mode. We reset it to unloader mode and
it ran cooler and cut our power consumption by a significant amount.

As to ganging the compressors, set the 7.5 to a 95-120 split, unloader
mode, and the second one to a 90-115 split, on-off mode. That way if
you sag below 95, the second
one comes on to boost capacity. If you watch your power consumption
prior to setting the 7.5 to unloader and then after, you will be
definately suprized at the savings, especially
if you are on a peak demand pricing contract for power.

Craig C.