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Eliminating priority valve from steering?

Discussion in 'Compact Wheel Loaders' started by Steve Bowman, Aug 24, 2018.

  1. Steve Bowman

    Steve Bowman Well-Known Member

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    Currently my loader is setup with a single gear pump for the hydraulics and steering. I assume the boom/bucket valve is open center.

    The orbital steering valve has a priority valve built onto it. The line from the pump goes to the steering 1st, then to the other valve. I must replace the steering valve and am considering one that does not have an integrated priority valve.

    If i just leave the hydraulic lines as they are and replace the priority valve with a tee, will the steering still function normally if i am not operating the boom/bucket controls?

    I do anticipate reduced steering performance if I operate the boom/bucket while steering.

    Any special concerns?

    Thanks
     
  2. willie59

    willie59 Super Moderator

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    We'd need more info on the actual set up of your machine to give accurate advice, but assuming your loader control valve is open center, and the main pressure supply line first goes to the steer orbit valve, then to the loader control valve, if you place a tee at the P port of a new steer orbit valve and run a line from that tee to the (open center) loader control valve then you won't have any power steering at all. But that's just the way I'm interpreting your post.
     
  3. John C.

    John C. Senior Member

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    I believe willie59 has it correct.

    Actually I hate to nit pick but steering is a safety issue and putting something in other than what was designed for the rig would be considered willful negligence should someone get hurt. Steering and brakes are always priority systems. A priority valve makes sure the steering is supplied first and that the use of other functions does not affect the performance of the steering system.
     
  4. Steve Bowman

    Steve Bowman Well-Known Member

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    John, I agree that the steering is important and I do not want to jeopardize safety. At this point we are just discussing things, but your point is well noted.

    Willie, You have it correct. Now that I think about it I would agree with you that there will not be sufficient pressure for the steering, if the valve is open center.

    However... every other orbital valve I have looked at does not have a priority valve built in. Set aside the systems with a dedicated steering pump. That could mean that there is a separate priority valve, or is it possible that if the hydraulic valve was a closed center, there would be sufficient pressure for the steering to operate? But with a closed center, my pump is constant flow, and would have to push oil through a relief constantly.

    Because in reality, my hydraulic valve needs replaced also. The spools are badly scored which makes it impossible to seal, and i would also like to add a 3rd section. But I don't want to get it wrong and overheat my oil by constantly pushing it through a relief.

    With the right mix of components, these systems are really rather straight forward. I just have to get it right.

    Say I keep the open center style hydraulic valve. Could I add a stand alone priority valve to supply the steering? That option seems very straight forward and easy to accomplish.
     
    Last edited: Aug 24, 2018
  5. John C.

    John C. Senior Member

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    What is the make and model of the machine?

    On thinking about this a little more I don't remember an orbital actually having the priority in itself. All the compact loaders I've had my hands on used a piston pump for propel and a double pump for steering and implements. Steering was prioritized off the steering pump and excess flow went to the implement valve to supplement flow. I've worked on larger loaders that used what was called a switch pump doing the same thing.
     
  6. Mark250

    Mark250 Senior Member

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    Hi John here is an hydraulic schematic for a cat small wheel loader and it includes a priority valve within the HMU
    upload_2018-8-25_9-39-31.png
     
  7. Steve Bowman

    Steve Bowman Well-Known Member

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    It is a Waldon 7000. The orbital valve is a Von Ruden, and the integrated priority valve is a Danfoss. The priority valve bolts on and covers all of the ports on the orbital valve and serves as the connection points for all of the lines.

    There is a small orifice between the P and the R ports on the orbital valve that is what is missing from the others I am finding.

    The gear pump is 25 GPM 2000 psi.

    Full disclosure... The original valve is available, I just would like to save $$ if possible. So, re configuring the system is not a have to case. But, if it allows me to have more common parts, that is an improvement.
     
    Last edited: Aug 25, 2018
  8. John C.

    John C. Senior Member

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    If you have room to add a priority valve it is feasible. Would you have to modify mounting brackets and make different hoses to accomplish that. You will need to factor in the extra labor of the new fabrication against the replacement cost of the factory unit. I usually like to have the owner make the decision for changes like that. Give them the estimates for either fix, ask them which they prefer and then stop talking.
     
  9. Jonas302

    Jonas302 Senior Member

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  10. Steve Bowman

    Steve Bowman Well-Known Member

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    Well, even if I did find one with the same dimensions. Ports are unthreaded, which by itself is not an issue, but see the little orifice in there? I assume that is important.

    Thus my stumbling block.


    check it out...
    20180825_214402.jpg
     
  11. Steve Bowman

    Steve Bowman Well-Known Member

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    I think the bottom line is that if I find a suitable orbital valve AND priority valve, it should work ok.
     
  12. Steve Bowman

    Steve Bowman Well-Known Member

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    I think I have found a donor. It is a Yale forklift. I plan on getting the complete control valve assembly and the orbital valve. I believe it is open center and what looks like the priority valve is built right onto it.

    Maybe, it will steer a little slower, as the lines on the forklift are one size smaller, I believe. And I have to see if the mast section of the valve can be modified for two way operation...
     
  13. Steve Bowman

    Steve Bowman Well-Known Member

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    Well, I got the parts from the fork lift installed, and while the hyd valve functions just fine, the steering leaves a lot to be desired. In fact, I do not think it is usable yet.

    Lots of steering input with very little reaction of the cylinder. With the loader setting, it will not complete a full stroke of the cylinder. the wheel gets hard to turn after just a few inches of stroke in either direction. I could do some more testing while in motion and such, but I think my initial concerns have shown themselves rather quickly... I think the orbital valve is just way to small.

    I do not know what the volume of the original unit is, but a quick check of the Eaton 211-1088-001, from the fork lift, shows it is a 5.9 cu in model. That is only about 97 ml. The original one is definitely an inch or two longer. Looking around, it seems that the largest "common" unit would be 350-400 ml. I assume that rating is volume per revolution? I can measure my cylinder and calculate what would be required to fully stroke it.

    On the surface, the larger volume unit would certainly reduce the number of revolutions the wheel must turn to fill the cylinder, but I am a little concerned that the currently installed fork truck system would not fully turn the loader. However... It is now setting on rather wide pneumatic tires, on stone, so the force required to turn it would certainly be greater than the previous narrow, solid tires. When I tested it, I was only at an idle, and did not have any pressure gage in the system. I think I will start with a pressure check, but I am not quite sure where to do it?

    Factory specs where steering 2,000psi - boom/bucket 2,500 psi. Looks like I should at least get 2,000 psi at stall with the steering wheel?

    Should I put it on the supply to the steering valve, or on one of the cylinder lines?
     
  14. Steve Bowman

    Steve Bowman Well-Known Member

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    Looks like the steering and aux hydraulics are individually adjustable.

    20180915_194452.jpg



    Looking at the photo below...
    I have no service manual, but the steering supply is the line on the left, and the supply from the pump is the one at the bottom center. I assume the larger port is for the main hyd pressure, but not sure about the smaller pipe plug above it.

    Also, while we are looking at this valve, the plugs just below the 2 and 3 contained some sort of small spool and spring. A check valve of sorts. Anybody tell me how it would function? I have them removed for now. I was thinking that they might close the center of the valve.
    20180915_194849.jpg
     
    Last edited: Sep 16, 2018
  15. Mark250

    Mark250 Senior Member

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    I haven't been following this thread much because of safety concerns with the steering alterations, but I would suspect that the plugs you mention are the load check valves for the two circuits labelled 2 and 3. there function is to support the load when first opening the valve until the pump oil can catch up. in other words the load wont drop when you operate the control lever
    Mark
     
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  16. Steve Bowman

    Steve Bowman Well-Known Member

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    Thanks mark. I reinstalled them and there was no apparent change in functionality. I had never encountered them before in any of the spool valves I have worked on.

    I get your concerns about safety, but I am turning over all the rocks to get this working. I guess, you could say I have more time than $$$. Or that is the way I have it prioritized, currently. Heck, one way or another, there are nearly infinite differences in hydraulic systems. There are more than one way to skin a cat so to speak. Done properly, one can be as safe as the next.

    Maybe the thread title is misleading at this point, as there still is a priority valve in the system.

    One strange thing is that currently the boom is controlled by the old mast tilt section. That fork truck tilt spool has some extra little ports in it for some reason. The one in the middle.
    View attachment 185552
    When raising the mast, it is normal, but when lowering it, if I just slightly move the lever, it lowers, but if I fully move the lever, the boom continues to lower, but there is a load on the pump.


    Back to the subject of this thread, increasing the rpm of the motor did not have any effect on the steering. But I was still only setting still. I am not comfortable driving the loader around yet.
     
  17. Steve Bowman

    Steve Bowman Well-Known Member

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    With a single steering cylinder that has an approximate size of 3"bore x 10" stroke, I get a piston side volume of about 70cubic inches, or 1,150 ml.

    So, with the orbital valve I have currently, that would equate to about 12 turns to fully stroke the cylinder from the piston side. Way to much.

    With a target of about 3 turns (lock to lock) to stroke the cylinder that puts me with an orbital valve of around 383ml. Which just happens to be in the range of the larger units available on fleabay.

    400 ml = 2.875 turns, and 315 lm = 3.65 turns.

    My pump puts out 25 gpm, or .42 gal /sec. The 1,150 ml is about .3 gal, so I should have plenty of oil available. If I spun the wheel fast enough, it would stroke the cylinder in less than a second.

    With a more realistic maximum operation of 3 seconds lock to lock.. That is 18.18 gpm. Given my admittedly undersized -6 hose size and length, I will loose about 330 psi at that full flow.

    All of that seems reasonable to me. Nothing that makes me say Oh ****!.


    I still plan on connecting a pressure gage either on the supply to the orbital valve, and/or to one side of the cylinder to see what the relief is currently set at, and probably turn it up to the 2000 psi range.

    Not exactly sure why the current setup won't turn the loader very well. Without pressure readings, I might as well be throwing darts.
     
    Last edited: Sep 19, 2018
  18. Steve Bowman

    Steve Bowman Well-Known Member

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    Well, my calculations where off just a little. I have a little over two turns lock to lock now with the 400ml orbital valve.

    A little quick, but definitely much more useable.