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  1. #1
    Platinum Member
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    Raleigh, NC USA
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    Massey-Ferguson MF 1220

    Default How does a 2-stage hydraulic pump work?

    This seems like as good a forum as any to post this question... [img]/forums/images/graemlins/cool.gif[/img]

    I'm referring to the type of hydraulic pump typically used on log splitters. It provides a high flow at lower pressure (to move the splitter wedge without resistance quickly) and a lower flow at high pressure (to move the wedge slower but with more force when resistance is encountered). How do these work internally to get the two different flows and pressures? Anybody know? It must be pretty simple, or it wouldn't be reliable (right?).

    I have a small tractor/loader whose "transmission" is a hydrostatic drive pump and 4 hydraulic wheel motors. One of the disadvantages of this design is that you only have 1 "gear"...slow! The thought struck me that some sort of two stage pump might give you more speed when there's little resistance and more torque when it's needed...kind of like a automagic gear-selector... [img]/forums/images/graemlins/shocked.gif[/img] Any thoughts?

    Also, many hydraulic pumps can also be used as hydraulic motors. Does anyone know if that's true of any of these two-stage hydraulic pumps?

    I'm not planning on modifying my current tractor, just curious. Who knows, I might decide to actually build something ludicrous one day, though!

    Dave

  2. #2
    Platinum Member
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    Winchester, New Hampshire
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    Kubota L3000

    Default Re: How does a 2-stage hydraulic pump work?

    There are several different designs when it comes to multi-stage hydraulic pumps.
    The one you refer to on a wood splitter is usually a 2-stage pump somewhat like your heart,
    two chambers with a vavle in between.

    There is a high volume low pressure chamber and a low volume high pressure chamber. When
    the resistance to flow is low in the hydraulic system (cylinder) the high volume low pressure side
    supplies flow to the cylinder. As the resistance to flow increases (splitting wood) the relief valve
    reacts to divert the flow to the low volume high pressure part of the pump until the pressure drops
    below the pressure setting of the relief vavle then the high volume low pressure side takes over.

    I"m not sure this type of pump would work as a motor also.

    Randy

  3. #3
    New Member
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    Redding, Cal
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    '39 Case RC, JD 110, White, Gibson D, modified Craftsman, homemade loader, homemade kids tractor

    Default Re: How does a 2-stage hydraulic pump work?

    ...but what exactly causes the pressure change. Large outlet orofice for volume and small outlet orofice for high pressure?
    Gary1944

  4. #4
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    Northern, IL
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    Branson 2400H

    Default Re: How does a 2-stage hydraulic pump work?

    On two-stage pump The pressure change is caused by work being done externally and not in the pump itself. These typically will not work as a motor.

    Using a two-stage pump on fixed displacement motor would provide you with two speeds depending on the pressure required to turn the motor.
    Artificial Intelligence will never overcome natural stupidity.

    Branson 2400H MMM & FEL

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  5. #5
    Super Star Member Egon's Avatar
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    Default Re: How does a 2-stage hydraulic pump work?

    http://www.multipower.us/pdf/hydraulic_pumps.pdf

    This site may be of interest.
    Egon
    50 years behind the times
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    Worn out skin bag filled with rattlin bones

  6. #6
    New Member
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    '39 Case RC, JD 110, White, Gibson D, modified Craftsman, homemade loader, homemade kids tractor

    Default Re: How does a 2-stage hydraulic pump work?

    I'm afraid your quote applies to me. I don't know what you mean by "work being done externally". I am thinking of this as a garden hose that I squeeze off at the nozzle and water shoots farther...so, I picture a smaller orifice makes the greater pressure.

  7. #7
    J_J
    J_J is online now
    Super Star Member J_J's Avatar
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    JACKSONVILLE, FL
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    Power-Trac 1445, KUBOTA B-9200HST

    Default Re: How does a 2-stage hydraulic pump work?

    When the pump senses the pressure caused by the load, some components shift to change from LO to HI pressure, and is automatic with the LO stage pressure preset at 500 PSI.

    http://www.northerntool.com/images/d...nuals/1053.pdf
    J.J.

    When I works, I works hard. When I sits and thinks, I goes to sleep.

    Git er done.

  8. #8
    New Member
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    '39 Case RC, JD 110, White, Gibson D, modified Craftsman, homemade loader, homemade kids tractor

    Default Re: How does a 2-stage hydraulic pump work?

    WOW! What a fantastic publication. Thank you a ton!

  9. #9
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    Default Re: How does a 2-stage hydraulic pump work?

    A 2-stage pump is just 2 pumps in one housing. Lets say we have a 11 gpm 2-stage pump. That means that the high volume side is pumping 8 gpm and the high pressure side is pumping 3 gpm. Now,when the splitters cylinder comes into contact with the block of wood. System pressure starts to build,When system pressure gets up to the pressure setting of the unloading valve. The unloading valve will open, the check valve will close. Pressure in the system will continue to build from the 3 gpm side of the pump. Meanwhile, the oil from the 8 gpm side of the pump flows though the unloading valve back to the supply"inlet" side of the pump

    How does a 2-stage hydraulic pump work?-2-stage1-1.jpg

  10. #10
    New Member
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    Redding, Cal
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    '39 Case RC, JD 110, White, Gibson D, modified Craftsman, homemade loader, homemade kids tractor

    Default Re: How does a 2-stage hydraulic pump work?

    Thank you George G. I got a great PDF file from Haldex that pictures the two gear pump components...but doesn't indicate what is different about the high pressure pump component. I tried to copy a link (or anything!) to attach here, but couldn't. So, now I know there are separate pump components at least.
    I have a gear pump that I hope to use on a logsplitter and hoped there was a way to get 2 pressures from the one set of gears. I suppose that is either not possible or too difficult/expensive. Thanks to all who replied.

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