Page 2 of 2 FirstFirst 12
Results 16 to 21 of 21

Thread: Compressor, CFM Increase, Pullies?

  1. #16
    Join Date
    Feb 2011
    Location
    Central WI
    Posts
    5,666
    Compressor pumps may or may not be rated to run within a range of rpms. If the same pump is used with different size motors to provide different cfm, you might be able to swap out but changing pulleys, motor, and starter electrics might cost more than it is worth. Quincy pumps were made to run from 600-1200 rpm but they were made a million times better than most aluminum head hobby level units. If your particular pump is also used on a larger motor at a higher rpm you might make it work. I'd sell it and find a used larger compressor with a larger tank though. More cfm benefits from a larger tank to cool the air and drop out the moisture into the tank. Used industrial quality compressors are pretty cheap and rebuilding them is pretty easy if needed. Dave

  2. #17
    Join Date
    Jan 2017
    Location
    Marina del Rey, Ca
    Posts
    1,934
    MH--good post.
    "Anything seems possible when you don't know what you're doing."

  3. #18
    Join Date
    Jun 2012
    Location
    New Westminster BC
    Posts
    2,981
    Quote Originally Posted by Mike Henderson View Post
    Just a correction - Induction motors are not synchronous motors. They always have some "slip" (the difference between the hertz and the RPM). As the motor is loaded (any loading, not just overloaded) the slip increases, which means the RPM decreases. The specification of the RPM of a two pole 60hz motor is usually 3450RPM which means that at full load, the motor will run at (approximately) that RPM. When loaded lightly, it will run at a higher RPM. When loaded beyond the specification of the motor it will run at an RPM less than 3450. The change in RPM is smooth (up to a point), meaning that if you add a small increment of load, you get a small decrease in RPM.

    If you load it enough the RPMs "crash" towards zero (the motor stalls). When you overload a motor, the motor is trying to create more HP than it was designed for. HP is torque times RPM (times a constant) so as you ask it to create more and more HP, the RPMs go down. If the motor cannot generate more torque to counter the slowdown in the RPMs the HP goes down. Once you reach that point, the motor stalls. Most motors can actually produce a bit more HP than the nameplate but they will be drawing excess current, which leads to excess heat. If continued, the motor fails from the heat.

    Even when completely unloaded, an induction motor will not run at 3600RPM. An induction motor requires some slip to operate.

    There are synchronous motors and those have an energised rotor - meaning that there are brushes and current is provided to the rotor. In an induction motor there are no brushes and the current in the rotor is "induced" by the difference between the hertz and the RPM.

    Mike
    Agreed, my terminology was not precise, my point was that putting a bigger pulley on a motor won't speed up the motor. Your explanation is more detailed and better than mine.

  4. #19
    From what I see on the specs, they have the same Pump, but different Motors and Pulleys, which I would expect.

  5. #20
    Join Date
    Sep 2016
    Location
    Modesto, CA, USA
    Posts
    9,885
    If you increase pump rpm you have to lower cutout pressure. Most are set at 150 PSi or higher. For most folks 100-120 PSi is more then enough.
    The real way to figure out cutout pressure is to run the bigger pulley until the amp draw is right at FLA. Read the pressure gauge and the set the cutout pressure a little below that pressure.
    Bill D.
    3-5Hp is the range where a two stage piston pump will be more efficient and worth the extra cost in energy savings. 10-15HP is the point for a rotary screw compressor and it's maintenance cost. A screw machine has to be run often enough and long enough to dry out the oil. that expensive oil has to be changed several times a year regardless of use.
    A piston pump is a better choice for those who do not run it for continuously for hours everyday
    Bill D

  6. #21
    1. You may strain/burn the motor with at added torque/load of the larger pulley.

    2. You may damage the pump with the increased rpm.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •