I'm rebuilding my 20 some year old speedy air compressor as an off grid soft start unit. The compressor went bad and it developed a pin hole leak on one of the welds. So I welded over the pin hole and took it to the local fire fighting supply store that does hydrostatic testing. They filled the tank with water, pressurized the tank to 250psi (the working pressure is 135max), held it at 250psi for 4 minutes and smacked it with a plastic mallet. So now that I know the tank is safe I'm building it back up.
I have found the only way to soft start a capacitor start motor is to uncouple the motor from the load, start the motor on a resistor, bring it up to full speed and full voltage, engage the belt with the compressor unloaded, close the unloader solenoid and build up air preasure.
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