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Unloader valve on compressor switch...

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  • Unloader valve on compressor switch...

    I'm refurbishing an old compressor and intend to put a new pressure switch on it. McMaster shows switches both with and without unloader valves. What determines whether this feature is necessary or desirable?

  • #2
    The switch unloader valve usually dumps pressure in discharge line before tank check valve.

    This allows compressor to spin a turn or two with-out load to facilitate starting.

    Some compressors have a centrifugal rig on crankshaft to do the unloader honors, and you don't need one on the switch.

    Hth Ag
    Last edited by agrip; 11-25-2009, 07:02 PM.


    • #3
      Thanks agrip, I guess I'll go with the unloader.


      • #4
        or you can go the third route like my old 2hp compressor uses, where you just plug the unloader port on your check valve poorly (see, pipe plug but no teflon tape used), or have a small hole drilled (like #80 small), and assume that it will be at least 10 seconds beween the compressor turning off and it comming back on again (pressure just constantly bleeds from before the check valve, making compressor about 1% less efficent due to leakage, but works well as an unloader)
        Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


        • #5
          On my compressor, a really cheap one, there isn't enough capacity in the feed line from the pump to the tank to allow the motor to come up to speed before pressure builds. Consequently it blows the breaker from time to time on start-up. I have to do something about that, since my alarm clock is on that same circuit.
          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


          • #6
            darryl: add a longer feed line Idealy that cooling fined stuff but copper pipe is fine too.
            Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.


            • #7
              Darryl, it's entirely possible your check valve is sticking at first. Maybe you should see if it's worn out and causing binding.