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Old gardner denver comprendo question...

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  • Old gardner denver comprendo question...

    this things from the 1960's - it's a two stage model ADK 1001 SN 5525599 great compressor --- on top of the heads it has the small classic little copper lines that are T-eed together and then run off to what we thought would be the pressure switch box --- yet the lines don't seem to have any pressure in them even when the unit pumps up and or is running or whatever, are these lines used for something else? perhaps they actuate something in the heads themselves? anybody know? thanks ahead of time

  • #2
    Maybe filled with crud?

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    • #3
      Its for "unloading" the compressor
      There is a timer which usually kicks off after about 15 seconds (Varies !)
      When the compressor stops, there is comppressed air in the chamber and that would stall the motor on a restart
      so the unloader valve dumps the air and allows the compressor motor to start without a tremendous load. (Amp draw too !)
      The copper lines will have pressure in them during running , and then they "Vent" the compressor.
      If you stand near a compressor when it stops, after 10 to 60 seconds you will hear a wooosh sound, that is the unloader valve as they call it
      Rich
      Last edited by Rich Carlstedt; 03-24-2020, 05:39 PM.
      Green Bay, WI

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      • #4
        Yes - Rich, that's what we thought and is the way we connected the lines --- but they don't "unload" they don't have any pressure in them, was just wondering if they are for another purpose other than the "obvious"

        it won't even make the little pressure needle drop that the pressure switch goes up against --- there's no pressure in the little copper lines...

        the unit does fire right up with no hesitation so really don't know if they are for something else or what, which I could find a pic of this unit to show but cannot find any info on-line...

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        • #5
          Many compressors have a mechanical unloader operated by a centrifugal valve attached to the crankshaft.

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          • #6
            Originally posted by Bented View Post
            Many compressors have a mechanical unloader operated by a centrifugal valve attached to the crankshaft.
            Yeah - those are built right into the unit's --- this is not one of those types - there is nothing on any of the sidecases for such a mechanism ...

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            • #7
              Originally posted by A.K. Boomer View Post
              ... to what we thought would be the pressure switch box ...
              Whatta ya mean "...what we thought ..."? Is it the switch box or not?

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              • #8
                Originally posted by Bob Engelhardt View Post

                Whatta ya mean "...what we thought ..."? Is it the switch box or not?
                Yes it's the switch box and everything is adjusted right the "what we thought" was referring to what Rich said, and is how we connected everything up as in conventional --- this may be one funny bird, just found out more info - it's a 250 psi air/gas compressor

                and these lines might be some kind of actuators for internal valving so they may not build pressure - they require tank pressure to actuate - once actuated he says it "free runs"

                the plot thickens,,, this was his Dads old compressor and he seen it operate this way but it's been many years and his dads gone now, it did not have a conventional shut off system... it would pump up to a certain level and then the lines would get tank pressure (regulated and adjustable) and then it would go into free run mode and then the unit was manually turned off... I know - I know --- but that's the way it was....

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                • #9
                  I worked in a power plant where the big instrument air compressors (like 200 + cfm) worked like that -- when pressure reached setpoint the unloader would hold the valves open, so the machine would continue to run but not pump any air, until the receiver pressure dropped to the low setpoint. I guess that's less wear & tear than stopping and starting every five or ten minutes.

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                  • #10
                    Originally posted by gmax137 View Post
                    I worked in a power plant where the big instrument air compressors (like 200 + cfm) worked like that -- when pressure reached setpoint the unloader would hold the valves open, so the machine would continue to run but not pump any air, until the receiver pressure dropped to the low setpoint. I guess that's less wear & tear than stopping and starting every five or ten minutes.
                    See I think you got it --- this thing was used on something like a 120 gallon tank or more with another compressor just like it - and it was for military purposes... but your describing just how it was connected...

                    He's only using it @ 125psi max - it bleeds down to 80 then it fires right up without drag --- so im going to tell him to just run it and keep using his pressure switch even though it does not unload the unit --- it does cut power when pressure is reached and then comes back on when needed... it's all good...
                    Last edited by A.K. Boomer; 03-24-2020, 07:22 PM.

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                    • #11
                      Some pressure switches have a pilot valve to operate the unloader. That allows no load starting.

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                      • #12
                        Originally posted by A.K. Boomer View Post
                        ....it did not have a conventional shut off system... it would pump up to a certain level and then the lines would get tank pressure (regulated and adjustable) and then it would go into free run mode and then the unit was manually turned off... I know - I know --- but that's the way it was....
                        Lots of the electric and gas engine twin tube "wheelbarrow" style compressors you see at construction sites work like this as well. When it gets to pressure, there is a valve that would use tank air pressure to disable the intake valves, so the compressor just freewheels. When the tank pressure drops to the cut-in, it unblocks the intake valves and the tank fill up again. I'd guess that's what those tubes on yours are for. Try pressurizing them while it's running and see what happens.

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                        • #13
                          thanks everyone - he's comfortable just running it as is now that he knows the original purpose and so am I now that i know the reasoning behind it -- and the 80psi kick back on pressure ? it does not even know its there --- this thing will last forever in this application... thanks again for verifying... I knew of the two other systems but never heard of this one....

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