Motor Valve Question (very basic)
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    Motor Valve Question (very basic)

    Hello,

    I am wondering if it is correct to connect 1(outlet)
    to 3(inlet), if you want to add a second hydraulic
    valve to your setup?

    And second this valve has a 5GPM specification,
    does this mean the valve restricts the flow to 5gpm,
    and the excess flow is directed to the outlet?

    So, if your motor is a 5gpm motor, and
    the PB system has higher than 5gpm,
    is this this how you do it? With a valve like this?

    Thanks

    Attached Thumbnails Attached Thumbnails hydMot_1.png  
    JD 4720, JD 445

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    Jim Timber's Avatar
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    Quick answer: No.


    The valve is rated for 5 gallons per minute because that's how big the internal passages are. If you push more than 5 gallons per minute through it, you will end up heating up your oil (and everything else with it = not good).

    I'm not sure what the best option to restrict the flow would be. There's flow control valves that are designed to do this, but I'm not well versed enough to tell you an optimal way to implement it.

    What are you trying to do?
    Last edited by Jim Timber; 05-17-2018 at 12:35 AM.
    5065E MFWD w/553 loader

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    Quote Originally Posted by Jim Timber View Post
    Quick answer: No.

    What are you trying to do?
    First, I'm only trying to get some answers, so thanks.

    I'm wondering about hydraulic motors, at the moment.
    It didn't seem inconceivable that this might be
    some sort of 5GPM regulator valve.
    But OK, no.

    So, how do you get a variable speed hydraulic motor?
    Is this where a proportional valve is used?

    I think I'm a little, or a lot, confused about pressure and flow.
    What determines how fast or slow a cylinder extends,
    or a hydraulic motor turns?

    Or what is a proportional valve proportioning, pressure or GPM?
    I can't see how it's not flow or GPM.

    In my valve above. It cannot flow more than 5GPM because of its
    fixed internal passages. And my motor will turn the same speed
    every time the valve is opened? And depending on the pressure,
    it will stall at different loads?

    I guess what I'm trying to do is confirm some things.
    (Or reject.)

    If this isn't too tedious, thanks.
    JD 4720, JD 445

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    AlKozak's Avatar
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    Quote Originally Posted by stone7 View Post
    First, I'm only trying to get some answers, so thanks.

    I'm wondering about hydraulic motors, at the moment.
    It didn't seem inconceivable that this might be
    some sort of 5GPM regulator valve.

    {...}

    What determines how fast or slow a cylinder extends,
    or a hydraulic motor turns?
    It's not a regulator, but a flow limiter. If it were an electric circuit, you'd model it as a resistor. The amount of pressure dropped across it varies with the flow. 5GPM is a meaningless specification without knowing the parameters surrounding it. Anyone can get 20GPM though a 5GPM valve given enough pressure and strong enough materials. I suppose with mobile hydraulics it is assumed to be something common like 2500 PSI and whatever is considered to be an acceptable pressure loss, but I don't know for sure. Unlike DC electric circuits, velocity of the fluid medium comes into play for some analysis and power lost in the restriction is not dissipated in the restrictor but imparted to the fluid as heat.


    All else being equal, the rate at which a cylinder moves or a hydraulic motor turns is determined by the flow rate. How much force it exerts is determined by pressure.

    Al
    Last edited by AlKozak; 05-17-2018 at 12:08 PM.
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    A variable speed hydraulic motor can be attained only one way: varying the displacement (gpm). BUT a vane, gear, or gerotor pump speed is change by changing the gpm TO the pump, usually a variable flow control valve does this. These are called "fixed displacement pumps". A piston pump has a "swash plate" (sp?) within the pump that at a constant displacement controls the stroke/displacement of the pistons which controls the output speed...1/4" stroke = "X"speed, 1/2" stroke = "Y" speed. These are called "variable displacement pumps".

    Hydraulics can...and usually is!...confusing without a basic knowledge. I'd suggest looking around online for "hydraulics for dummy's" or "hydraulics 101" and get some basic understanding of what goes on and why. That said, you can still continue here with questions and someone WILL help! Bob
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    Quote Originally Posted by rwmeyer View Post
    A variable speed hydraulic motor can be attained only one way: varying the displacement (gpm). ..., usually a variable flow control valve does this. ... WILL help! Bob
    So, I have an old JLG lift, with, what they call, proportional controls.
    I've always thought that all the control was going on in just the valves.

    I thought the spool was being moved faster or slower, and that somehow
    each coil of the valve was playing a sort of tug of war against each other
    to either be held(stop flow) or move(open up) at the speed(flow) desired.

    Is this even close to what's going on?
    Are these so called proportional valves what you are calling,
    "usually a variable flow control valve"?

    On this machine, I didn't think the pump varied at all. I thought it just
    supplied pressure and enough flow to drive everything. And I thought this
    is more or less what a power beyond is as well.
    JD 4720, JD 445

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    AlKozak's Avatar
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    Quote Originally Posted by stone7 View Post
    So, I have an old JLG lift, with, what they call, proportional controls.
    I've always thought that all the control was going on in just the valves.

    I thought the spool was being moved faster or slower, and that somehow
    each coil of the valve was playing a sort of tug of war against each other
    to either be held(stop flow) or move(open up) at the speed(flow) desired.

    Is this even close to what's going on?
    Are these so called proportional valves what you are calling,
    "usually a variable flow control valve"?

    On this machine, I didn't think the pump varied at all. I thought it just
    supplied pressure and enough flow to drive everything. And I thought this
    is more or less what a power beyond is as well.
    Variable displacement pumps are common in closed center systems where the required functionality is more demanding - multiple hydraulic devices that need to be controlled simultaneously and independently.

    From an engineering perspective, a valve spool is just like a variable resistor in an electric circuit. It's not very efficient but, more important, it does no regulation. The amount of flow and the pressure drop are entirely dependent on the motor load and setting of the valve. As the load increases, the flow through the motor and valve drops while the pressure on the motor side of the valve increases. You act as the control computer and decide whether speed or torque is what you wish to control by varying the valve.

    A lot of SCVs carry a warning that they are not intended for hydraulic motor use. Why, I do not know.

    Al

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    Jim Timber's Avatar
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    Quote Originally Posted by AlKozak View Post

    A lot of SCVs carry a warning that they are not intended for hydraulic motor use. Why, I do not know.

    Al
    Because they lock the ports in the center position. Say your motor is humming along spinning something like a ditch mower, you go from full flow to stopped by moving the spool to center - all the vanes in the motor are now hydrolocked and it blows up.

    Motor spools gang the A and B ports together when the valve is not applying fluid. When you take the mower in the previous example and remove power, the fluid just keeps on flowing round and round inside the motor and lines without any force applied.
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    For a good visual depiction of how a variable displacement pump based on a swashplate design works, look here.

    Al

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    Quote Originally Posted by Jim Timber View Post
    Because they lock the ports in the center position. Say your motor is humming along spinning something like a ditch mower, you go from full flow to stopped by moving the spool to center - all the vanes in the motor are now hydrolocked and it blows up.

    Motor spools gang the A and B ports together when the valve is not applying fluid. When you take the mower in the previous example and remove power, the fluid just keeps on flowing round and round inside the motor and lines without any force applied.
    Great explanation, thanks!

    Al
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