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Neil, not to be nit picky but on the older compressors, the rule of thumb cfm/hp is more like 2.5 (2.5cfm/hp) The electric motors are much less efficient too. While the compressor head my be in excellent condition like the old Westinghouse I worked on last week, the motors are just too old to be of value anymore. On this unit, the motor ran fine but was only a 2 Hp and drawing upwards of 22 amps. While not being overworked or overloaded, the amp draw was normal. I replaced this motor with a new 3 Hp (220v / 1ph). Upped the speed on the compressor head 150 rpm to 650 (upper limit of head). New motor runs full load at 11.8 amps and cut the run times as follows: On at 110 psig off at 145 psig- was 8.9 minutes, now 4.5 minutes. Just about cut the amps and run time in half. Saves a lot on the electric bill. BTW, this compressor has to be from the 1950's and ran with no air filter for God knows how many years. I was called in because it was no longer building air. Cleaned the paint, dirt, leaves and strings from the check vlaves and it worked fine. Shocking part of this was when I pulled the heads, the pistons and bore look as good as day one when it rolled out the plant door despite no filtering of intake air. If this had been my unit, it would have died 30 seconds after taking the filter off.
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