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Thread: Pressure variation in Rotary pump.

  1. #1
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    Pressure variation in Rotary pump.

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi guys, just hooked up a new pump to my LSM, and the pressure variation seems to be too high.

    My previous pump (the one that came from LSM) had a slight variation of the pressure guage needle, hovering around the 9 bar mark.


    The new pump seems to vary much more, fluctuating constantly between 8 and 10 bar. And when i say fluctuating constantly, i mean exactly that, bouncing in a blur of needle between 8 bar and 10 bar, not randomly adjusting its fixed position.


    Is it just me, or does this seem too much variation?


  2. #2
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    Re: Pressure variation in Rotary pump.

    sometimes with new pumps and with ones being used the seal in the pump bypass sticks to the side wall
    when this happens you can get the bounce you talk about
    removing bypass nut and insert from body (this is the lump on the side with a screw in it) careful not to drop guts inside pump,
    (for first timers this is best done with pump out of machine with the bypass facing downwards towards the bench)
    remove the piston in the nut, clean and lubricate, make sure the piston slides cleanly. reinstall and adjust pressure by way of the screw.

    with older units dirt and scale builds up on the oring causing it to stick. when this happens get a small piece of wet and dry sandpaper, roll in to tube shape insert in hole and slide it in and out numerous times until the surface is clean

    gauge fluctuations can also be the problem of the gauge or scale restrictions in the copper tube leading from gauge to water line

    remember gauges on the machines are only used as a guide, and in many cases are not accurate.

    hope this helps
    graham
    havent worked out how to insert picks yet

  3. #3
    Mal Dimal's Avatar
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    Re: Pressure variation in Rotary pump.

    Quote Originally Posted by fix link=1200985964/0#1 date=1200992224
    havent worked out how to insert picks yet
    Here you go Graham,

    Hope this helps you out :) ...... http://coffeesnobs.com.au/YaBB.pl?num=1187136315

    Mal.

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    Re: Pressure variation in Rotary pump.

    hmm thanks for the suggestion fix.

    ill have to pull it apart this weekend and have a look.

    So basically i just tip the pump on its side (screw facing down) and undo the screw until the piston slides out? (and put it back in the same fashion?)

    Is this part in contact with the water? if so what lubricant can i use?



    cheers,

  5. #5
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    Re: Pressure variation in Rotary pump.

    hi if you follow the link you will get a rough idea of the bypass/ relief valve setup

    http://www.proconpumps.com/PDFs/Exploded%20View.pdf

    on the new pump you have the bypass nut is bigger and houses the screw and relief (different make same idea)

    check to see that the piston moves freely in the nut housing a smear of food grade grease or vasoline will do

    dont unscrew the adjusting screw. if you do you will need to reset pressure
    graham

  6. #6
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    Re: Pressure variation in Rotary pump.

    hmm i think i know what you mean now.

    The adjusting screw seems to be set inside a larger nut that looks like it can be removed as well. I assume that this is the Gino Rossi equivalent of the Procon Acorn Nut?

    Also, when you say piston, do you mean the part the Procon diagram calls a "releif valve"? or am i looking in the wrong spot?


    Also, i seem to recall some kind of strainer screen actually inside the intake line of the pump? Is this normal as the Procon has it inside a seperate area?

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    Re: Pressure variation in Rotary pump.

    this is what the bypass assembly looks like, your nut is bigger.

    from the left we have the

    filter- plunger or piston with oring - spring - nut body - adjusting screw
    sorry for confusion



  8. #8
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    Re: Pressure variation in Rotary pump.

    ah okay, cheers for that.

    Going to pull it apart tonight and take a look.

    If all else fails i guess ill just put the old pump back on, and make sure the varition isnt the same.

    If it is, its more than likely the manometer i guess.

  9. #9
    Mal Dimal's Avatar
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    Re: Pressure variation in Rotary pump.

    Just wondering Zak...

    Have you noticed whether there is a Check Valve in the Down-stream hydraulic circuit from the pump? Sometimes these are fitted to the wrong side of a pump and can cause the sort of fluctuation in pressure that you are noticing. If there is one there, it needs to be moved to the pipework on the suction side of the pump. Its purpose is too ensure that the pump internals are always flooded...

    Cheers mate,
    Mal.

  10. #10
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    Re: Pressure variation in Rotary pump.

    My previous pump (the one that came from LSM) had a slight variation of the pressure guage needle, hovering around the 9 bar mark.


    The new pump seems to vary much more, fluctuating constantly between 8 and 10 bar. And when i say fluctuating constantly, i mean exactly that, bouncing in a blur of needle between 8 bar and 10 bar, not randomly adjusting its fixed position.


    based on this description more likely new pump
    Fix

  11. #11
    Mal Dimal's Avatar
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    Re: Pressure variation in Rotary pump.

    Quote Originally Posted by fix link=1200985964/0#9 date=1201249373
    [color=#cc9900]based on this description more likely new pump
    Fix
    Hmmm, true.... but the new pump may also be more efficient and exacerbating the apparent problem, if it really is a problem worth worrying about. Could be that the gauge is also severely under-damped? Not easy when the machine isnt in front of you fix,

    Mal.

  12. #12
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    Re: Pressure variation in Rotary pump.

    hehe sorry guys im not sure what you mean.

    Whats more likely the new pump?

    and whats under-damped?




    Also, i pulled it apart today and there are a few variations in the pump design. In addition to those parts shown in the picture above, there is also a spring and ball bearing which go on the end of the piston (and the piston is one piece of brass with an o-ring attached to the end, rather than that white plastic piece being seperate).

    I lubricated the brass piston, and the hole in the part that unscrews that it slides in and out of with some vegetable oil.

    It seems to have made a small difference, and it is definitely quieter than before.


    However the variation is definitely still present.


    As for the check-valve, im not sure what you mean. The only thing i saw inside the pump was a white plastic thing that looked like a filter...pretty sure that was in the intake side.


  13. #13
    Mal Dimal's Avatar
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    Re: Pressure variation in Rotary pump.

    Quote Originally Posted by Zakal1 link=1200985964/0#11 date=1201509320
    hehe sorry guys im not sure what you mean.

    Whats more likely the new pump?
    The new pump being nice and tight with respect to internal clearances and fit, will be slightly more efficient at moving water through itself. This is not a bad thing.

    and whats under-damped?
    Line Pressure Gauges that are fitted relatively close to the pump will normally have either built-in damping to "smooth out" the pressure pulses from the pump output or a small accumulator like device in parallel with it (similar to the anti-hammer devices you fit near your washing machine taps). If yours has neither then it may just be that this is something that you will have to live with or involve a competent espresso machine tech, to rectify for you.

    As for the check-valve, im not sure what you mean. The only thing i saw inside the pump was a white plastic thing that looked like a filter...pretty sure that was in the intake side.
    If there is one fitted, it will be a separate slightly bulbous brass fitting (similar to Part #700011 here) in the line going to the pump. If it has been fitted on the high pressure side (the wrong place), it will be fitted into the downstream piping somewhere and not necessarily butted up against the pump. It is also quite possible that your machine doesnt have one fitted at all.....

    All the best,
    Mal.

  14. #14
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    Re: Pressure variation in Rotary pump.

    Behmor Brazen - $249 - Free Freight
    hmm okay, looks like its probably the pressure guage then....which means my old pump was probably still working fine (mostly). Oh well.



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