Nice!
How does it compare to the old pump, piston-size wise and speed wise?
This is a much larger compressor, also twin but parallel twin instead of 90 degree V. This makes the pump deliver two strokes every revolution, one every 180 degrees so there isn't any higher order harmonics. A 90 degree V twin does two strokes every revolution too, only they are 90 degrees apart, with a 270 degree "dead zone". This is why Harleys have that "potato-potato" exhaust note.
This one also turns at 950 RPM. But because the pistons have three compression rings, all lubed by oil, it has much less blow-by. So the advertised rate is more realistic than oil free compressors that have one piston ring which leaks, cracks and runs hot.
Finally, the slower piston speed of a belt drive means less compression heating. This makes it more efficient because the energy from the motor is turning into cooler compressed air.
I sized the motor pulley to run it at the higher RPM range since the motor is a 4+ HP. Because it is rated for 145 PSI and the switch is a 120 PSI, the higher RPM isn't an issue. Since the unit has a good unloader, the compressor doesn't start at a 90 PSI dead head but rather the pump and line to the tank is drained. This lets the motor's start capacitor to spin up to where the motor will make more torque. The 60 cycle power has a condition where current lags voltage, a start capacitor corrects this and once the motor is up to about 2000 RPM, a centrifugal weight-spring system switches that off, relying on the run capacitor (the two bulges on the motor are the capacitors).
I could have suggested the larger compressor, rated for 5 HP and ran it slower but that is an overkill. Safety here is from the 120 PSI operation of a 145 PSI rated compressor, even though it is running at the upper RPM range. The motor is rated at 14 amps max running, that is 3220 Watts. that is 4.32 electrical horsepower. Sure, lock the rotor and the current will go to 20 amps, there you can say it is a 6 HP motor but it isn't doing any work. Take the SCFM ratings on many compressors with a grain of salt, that is under hypothetical situations.
Compressors are just reverse engines. Just like (some) generators are reverse motors. Or air conditioners are reverse steam engines. Thermodynamics, the laws were only discovered by humans. Nature wrote them. This is why engineers are better than lawyers
. Will need another 125 of argon soon.
