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Help on Propane carbureted scissor lift. Seems to be going lean on fuel.

Discussion in 'Forklifts/Telehandlers' started by fastline, Jul 7, 2016.

  1. fastline

    fastline Senior Member

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    Here are some pics with notes. However, I think you are onto something! I know for sure there is a fast/slow switch on the pendant and it does work. However, that is obviously a flow control not a pressure control and my problems are pressure related. You can just hear that valve block screaming when it is dumping all that pressure off. I will look at the electrics again and try to find it! That just has to be it!!! I was ready to chase down a relief valve because I just know it is not getting enough pressure.


    Could we possibly say that the solenoid is defaulted in the low pressure position and needs power to get full 1800psi as a default safety? I would highly doubt any safeties are left on it! Hell, it doesn't even have brakes! I have to setup RR ties on the driveway as a safety when testing because if the engine cuts out, I have no way to stop!

    If I can get full drive power, I can for now operate with a spotter and wheel chalk to just get things done.

    Thank you again!
     

    Attached Files:

  2. lantraxco

    lantraxco Senior Member

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    Yes, according to the hydraulic schematic, if it's drawn properly, the default is to allow oil to pass to the low pressure relief, so you need power to the coil to activate the valve which will close off that line and increase the pressure.

    Best guess and it should be safe and easy to try, on the close end of the manifold there, there's a large square section bolted on with two solenoid coils close together right on top. The book says this is the drive section. The Yellow lead is obviously the common ground for all the coils. The coil on the right has a wire connected to it, I'm guessing this is high/low speed, you could verify that if you wanted to by simply unplugging either wire from the coil. The coil on the left has no wire connected to the top terminal. Best guess this is the Hi Torq valve. Connect power to the coil and try driving. If the right hand coil is actually the high and low, just pull that wire off and move it to the other coil for testing purposes, see what happens.

    I bet this will be a nice unit, you get her knocked back into shape a bit!
     
  3. fastline

    fastline Senior Member

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    LOL. I found and did exactly what you described as you typed it. All I did was verify that RH solenoid was in fact the hi/low in which all of this is proximal to the motor drive part of the block. Other solenoid had no wire. I swapped it around confirming that no power to hi/low defaults to low. What I did find is without brakes, this makes for a BIG issue in high torque! That thing will straight rip ass and after it was rolling down the rock driveway a bit, I reversed to slow it, and it spun the tires and returned in the opposite direction real damn quick! Too quick. I am sure that ain't good on anything and I about stalled the engine.

    I am thinking a momentary switch for the hi-torque for now. I really need that machine like yesterday but I sort of need brakes.

    So again, if I repaired a brake (assuming I can find parts, Ross motor/brake unit), and ran a line to it from that brake port on the block, will it drop pressure off correctly when drives are enabled?

    As a quick fix for now, I figured I could just install a needle or ball valve on that line and all I need to do is trap pressure in the brake so I could run it up on the riggers, fire the drives, and close the valve.

    As for the rest of the unit, the hydro oil is crystal clear, engine runs like a top now other than some minor tuning I need to do, lift works nice, riggers work nice, and a huge 6x12 platform. Not a bad rig. Rather have a boom lift but the price was right.
     
  4. lantraxco

    lantraxco Senior Member

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    Well, that's progress at least.

    Actually Ross motor, MICO brake, which is a good thing I think, parts wise.

    View attachment MICO Brake.pdf

    A SUN counterbalance unit with brake shuttle will run you about $400 or so, I would seriously recommend looking into that, if you have a local hydraulics outfit they can help you dial in the specs. Something like this should be close: http://www.sunhydraulics.com/model/YCCW
    Will give you hydraulic braking before the spring brakes come on, supply brake release pressure and will take some of the snap out of the on/off.

    If you go the needle valve route get one with a free flow check, so oil pressure flows freely to the brakes to release them, then set the needle so it takes a couple seconds to completely lock back up.

    If you need it to be towable should the engine fail or whatever, you will need a valve like this anyway, and one plain needle plumbed so it tees into both motor lines, you close the brake needle, activate the drive to release the brakes, then open up the bypass needle to let oil flow as the motors turn.
     
  5. fastline

    fastline Senior Member

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    You know your stuff Lantraxco.

    i think I might need some schooling on the counterbalance valving to better understand things. This valve will be able to cushion things and function as the brake release? Links and docs are great to soak up some principals of operation.

    I can tell you, maybe because the brakes no worky, that thing is very jerky. I am used to machines with variable controls. Let me just ask for the sake of asking, do you need special valving to modulate the flow rates on these valves? I know we need to vary the throw of the spool but was not sure if i varied the voltage to the solenoid, if that will function as intended or if you need a special valve setup?

    It may be easier to consider improvements hydraulicly. just trying to learn. it is pretty obvious the fast open and close of the drive motor valve needs a little buffering.
     
  6. lantraxco

    lantraxco Senior Member

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    Now and then I get a little wood on the ball. :)

    I can't really find a good explanation of the counterbalance setup, or what some folks call a "dual overcenter valve"

    The SUN link I posted shows a functional diagram, that manifold has a shuttle valve for the two pressure lines from the valves (v1 and V2) whichever is hte higher pressure is directed to the brake port. The next two valves marked CBCA are the counterbalance valves, one for each line. They have free flow checks to allow oil to pass to the motor as pressure builds on one line, let's say V2. The opposite side carries oil coming out of the motor, but it's stopped by the counterbalance valve.. as pressure builds on the inlet of V2, it's carried by the dotted line over to the opposite valve, where it opens the counterbalance valve which throttles the outlet oil passing out of V1, maintaining a backpressure on the motor outlet. If you start to run downhill say where the motor tries to run faster than the oil coming to it, pressure on the inlet drops and the valve on the outlet side will throttle down to maintain the pressure.

    The two other valves marked RDDA are fast direct acting relief valves set up crossport so in any case where pressure exceeds a safe setting they pass oil across from one line to the other. These are for sudden spikes like when you start or stop moving and if for some reason the machine gets pushed or on too steep a slope a valve will open to release pressure rather than damage the motors.

    By the way, just noticed that SUN manifold is designed for use mounted directly to a charlynn motor so don't order that one, sorry.

    As to modulating the valves in the machine, I'm betting they're not really made for that, pretty much on or off, and the coils probably wouldn't like it either. Yeah, the valve you have is what's known as a slam-bang valve, on or off only. For feathering you would need a proportional valve. Since there's a single pressure line going to the forward/reverse drive valve it would be possible to put a single proportional valve in that line from the manifold if you wanted speed control. Just select forward or reverse and then dial in the speed you want maybe.
     
  7. fastline

    fastline Senior Member

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    Great! a few things to confirm.

    One function of the counterbalance is modulating the output side of the motor to get consistent speed/load on different grades without the engine constantly hunting to match to load?

    It would also add a short circuit relief valve but not sure when that might be needed if the motors go to drain when the the main valve is close and when open the main system relief should take care of that?

    I am trying to figure out how this will work with the brakes and if the brake port that is on the current manifold may provide the correct function directly? Seems like the block has some of this built in.

    However, I know that buffering the way this rig functions needs to happen. The way it would start and stop. I think if the brake works right to slowly engage/disengage, it could work well to buffer things since a delay on release can kind of stop the drives from jolting and a delay on stop could sort of coast things a few inches to a stop rather than a dead stop.

    Another question on the brakes, before I jump into them, is there anything that is going to be insane sucky about working on them? bolts with insane tension, shrink fits, etc?
     
    Last edited: Jul 11, 2016
  8. fastline

    fastline Senior Member

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    OK, after some thought, my ideas will not work. That brake port on the main block would have no way of knowing when the motors are fired because main system pressure is just remoted over to the main motor spool valve. I feel certain the OEM system used a counter balance valve to keep things moving nice and smooth. Why someone ripped all that out is way beyond me!

    I was then thinking about a relief valve on the drain line of the motor spool but two problems arise, A, there are two pressures to deal with 900/1800 so that might be interesting. B, I would have no freewheel function left to tow the machine if needed and I already have the towing frame which will be handy.

    I would really like to get the motors under better control for downhills but for now, it might be best to simply try to get one or both brakes working. This brings me to my questions of how we set that up to get pressure to the brakes? I realize as it works now, the dump side of the motor spool simply dumps directly to the tank but I think that pressure has to stay under 100psi to keep brakes released. I will probably need to plumb something in that connects to both motor sides and regardless of which side is hot, sends pressure to the brakes, hoping of course that 1800psi is OK for the brakes but I read that though it might only take 200-300psi to release them, they are made to do this.

    Lantrax, I believe you mentioned the CB valve doing just this while also adding the other functions. I guess I could see if I could get the factory valve but that will be a long shot. I think they had two valves for freewheeling. One locks pressure at the brakes to release them, the other might have bypassed the motor dump side relief so the motors would freewheel.

    EDIT: Damnit, that might not work either! Thinking more, on a decline, gravity may take over and though the motors seem to have control of the load right now, I am betting the inlet or P side of the motors in that situation is near nothing. If we would be looking for pressure in those lines to operate the brakes, that could be quite a problem in that the brakes would come in due to the loss of pressure and could be a damaging event. I can't really see a way around this other than do it right and use a counter balance valve with relief valve on the outlet side which would maintain pressure on the P side of the motor thus holding the brakes off while also better controlling motion.

    Never an easy way.....
     
    Last edited: Jul 11, 2016
  9. lantraxco

    lantraxco Senior Member

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    I think you can use the brake port on the manifold if you want, when they added the CB valve it was a lot closer to the motors so they used the shuttle and brake port in that to provide brake release. The existing brake port will have pressure any time you turn the motors on, as long as there's sufficient load to provide backpressure. As you surmised on a downhill or even just running ahead of the pump after the initial surge, incoming pressure will drop and the brakes will come on. Your idea of adding a relief in the return from the directional valve is not bad, I happen to know that style valve will deal with some back pressure. Maybe something on the order of 300 psi would at least give you some drag, without losing too much drive torque. But it will only work when the motors are on, the second the valve returns to neutral all ports open to tank and you lose the braking effect.

    You mentioned the crossport reliefs in the CB valve, due to the nature of the CB valve it locks the oil on the motor side, so even though the directional valve is open to tank, you need reliefs to allow oil to cross from one side to the other in case the motors are submitted to excess torque, or you get a spike starting or stopping. I can't find a spec in the book but typically these will be set somewhat lower than system pressure to provide some cushioning effect.

    I'll ask my local vendor if they can suggest a CB valve manifold unit.
     
  10. fastline

    fastline Senior Member

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    I think what I my concerns are with the brake port on the main manifold is there is really no way for that port to know when the motors are running or not. There is nothing in that block that is fired when the motors run. There is no additional spool or such. I am wondering if it was an option on the block but was never used. I know the plug in that port appears to be factory installed.

    Every coil on that block as been accounted for so not sure we could use that option without additional configuring. Probably smarter to just install a CB with shuttle that is a one shot deal. I just cringe that the tuning though because if the dual pressure situation. Have to tune it for the lower pressure of 900psi.


    The the short circuit relief, I am wondering if that would be needed since all motor ports go to drain when motor spool is in neutral.

    I can sort of see why you would not want to freewheel this machine for 20 miles though. It seems the motors would be spinning without oil.
     
  11. lantraxco

    lantraxco Senior Member

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    That had me going for a bit too, but here's how that system works: Since the pump is turning all the time, oil flows continuously through that manifold, the flow gets divided at the high/low speed valve in low, part of the oil goes off to tank there in low speed. The rest of the oil flows on to the external directional valve and since all ports are open in neutral, it just goes back to tank. When the directional valve shifts into either forward or reverse it closes off the passage to tank and the pressure line connects to one of the motor lines. The back pressure from the motor raises the pressure all the way back to the pump and that pressure is seen at the brake port as well.

    Not sure what you mean by tuning to the lower pressure? Do you mean tuning the CB valve or?

    The crossport reliefs: tried to explain that in post #29. The CB valve closes off the motor lines and locks the oil flow on both lines in and out of the motor, so the motor spool is irrelevant to the motor, it's only open on the backside of the CB valve, not to the motor ports.

    This page applies to freewheeling: View attachment Towing.pdf

    So unless you can get the drive wheels up off the ground, I would say you would be limited to about the length of a football field before the motors started heating badly, just a guess.