Typical pump assembly

Discussion in 'Fettling Forum' started by kerophile, Mar 13, 2010.

  1. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    Hi, I thought it might be useful to post some photos of a typical pump assembly from a classic brass tank stove:

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    The pump is a clever design. The whole piston assembly is designed to "float" between the shaped radius at the end of the reduced section, and the small nut on the end of the pump shaft.

    On the push stroke the piston seats on the radius and this forms an air-tight seal. Air is pressurised and is forced through a non-return valve into the tank.

    On the pull stroke the piston assembly moves to the nut on the end of the reduced section, and air can now enter the cylinder past the radius section.

    On the majority of pumps, such as this one, the piston assembly is like a drilled bolt and nut, which traps the leather washer in the correct position, and slides on the reduced section of the shaft.

    One or two manufacturers used a simpler but adequate piston, where the leather "bucket" sits between two steel washers. This piston design relies on by-pass flow, past the periphery of the leather washer on the back-stroke.

    Best Regards,
    Kerophile.
     
  2. Knight84

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    Thank you George!

    It amazes me how much things change over the years but how many things stay the same. Many new pump use this idea ... sadly have gone with washers.

    Cheers,
    Jeff
     
  3. presscall

    presscall United Kingdom SotM Winner SotY Winner Subscriber

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    Bloody hell, George, I'd not realised that was what was happening. Seriously. I guess I'd thought the air was getting past the cup washer on the 'pull' stroke!!! Bloody hell.

    Thanks for pointing that out. You have an un-erring eye for essential details. Brilliant. Thank you.

    John
     
  4. kerry460

    kerry460 Australia Subscriber

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    G,,day, the smaller the pump tube diameter, the more important the floating cup is, the small diameter will let very little air past the leather cup.

    kerry
     
  5. bluecat

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    Many thanks kerophile, you revealed another gem of knowledge to light my journey through the world of stoves.
    Many thanks.
     
  6. redspeedster

    redspeedster Subscriber

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    Some info that might help save a few pump rods. To change a pump leather, I don't usually remove the small nut at the far end of the pump rod. In my experience these are usually peened & you only have so many chances to remove the nut before the threads are knackered. If you remove the pump knob, remove any spring, grip the brass pump cup carrier with vice grips or screwdriver in the slot, you can remove the retaining nut and slide the old washer off the rod. Refitting the new pump cup is just the same in reverse.
     
  7. bluecat

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    That's exactly what I have done but I honestly think its the wrong size washer. Although it is smaller than the other one that came in the kit, I will get another kit for the 210 and try again.

    Thanks for your help redspeedster.
     
  8. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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  9. IvanN

    IvanN United States Subscriber

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    I did not understand this either! Thanks
    Ivan
     
  10. Murph

    Murph United States Subscriber

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    Here in the US, Coleman stoves and the like let the air slip around the outside of the leather cup and piston, the piston doesn't use any float to make it work right. Moving your thumb off the pump knob vents any excess pressure, so once the piston is pushed down, it's down.

    Murph
     
  11. kerophile

    kerophile United Kingdom SotM Winner Subscriber

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    “Going in from the top”

    Sometimes when stoves were manufactured, the only way to ensure that the retaining nut on the shaft will not come off in long-term use was to “peen” the bottom end of the pump shaft. This can make changing a pump leather very difficult, if not impossible.
    One solution, described by Ron, is to “go in from the top of the pump shaft:

    Replacing Leather Pump Cups

    Best Regards,
    Kerophile.
     
    Last edited: Jul 6, 2019