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Dump trailer hydraulics. General question.

Discussion in 'Trucks' started by Tony Wells, Feb 26, 2021.

  1. Shimmy1

    Shimmy1 Senior Member

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    What we really need to know is the current valve for the two line wet kit on the truck, or on the trailer. If it's on the trailer, it should be pretty simple, but the operators are going to have to be competent. To run both single and double acting hydraulics with the same kit it will take two valves, and really three lines (if the double acting trailer doesn't have a valve, which I will explain later). One line that will be exclusively used for the single acting system, and the other two will be used with double acting. Crane Operator explained it well, but I think he's only using constant flow if he's not using a single line. A sidedump would be a good example where you will need two valves on the truck if the trailer doesn't have it's own valve. Use first line and standard up/down valve for single acting. For sidedump operation, use other two lines, move standard valve to "up", and second valve (double acting valve) operates the sidedump. When finished, move first valve back to "down" and away we go.
     
    Last edited: Feb 27, 2021
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  2. John C.

    John C. Senior Member

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    The question that I have is why would someone use a double acting cylinder on a dump trailer. Is this a side dump or something. You can't run a double acting cylinder with a single acting hydraulic valve. If you extend the cylinder on A port the air or oil on the other side has to go somewhere. That's not the problem though. It can leak out through a breather or out the rod packing. When you shift the valve to the down position or out the B port, that oil has no where to go, so it just dumps over the relief valve and loads up on the engine plus creating a lot of heat.
     
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  3. Tony Wells

    Tony Wells Senior Member

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    Well John, in a nutshell I think you summed up my concern. With the regular two line double acting cylinder, I'm thinking the valve is a closed center spool that holds the dump bed where you release the operating lever, as in locking the gate and spreading gravel or something. When in that position, the PTO is still driving the pump, so the pressure is bypassed back to the tank pretty much unimpeded so it doesn't get hot. Then to lower the bed, moving the control to that position either (on a double acting cylinder) allows the butt end of the cylinder to dump back to the tank while pressurizing the top section of the cylinder. With that valve scenario, at all times there is a path for excess oil to return to the tank, a hold position that also allows that, and in both raise and lower positions whichever is the relieved end of the cylinder is open back to the tank.

    So then, the standard double acting cylinder valve should function normally; it has a pressure to cylinder position, a hold position, and a dump position to lower the bed. It's just the second line that I am unsure what to do with, other than provide a hose back to the tank so that no matter what position the valve is in, it cannot develop dangerous pressure. Then just provide a filtered vent for the non used cylinder port.

    Then enter the logistics of rigging which truck(s) for this, if any mods are required. And whether it is safe to do so. I still seems more correct to just swap to a double acting cylinder so that all the trailers were the same, and all the trucks would be compatible. I may even have a cylinder suitable. This all came up suddenly, and very well may just disappear. This request comes from someone other than the owner, who is keenly aware of complications involved when changing things on trucking components. He's a pretty sharp guy and may not want to do this at all.

    I'll present this to him over the weekend and see how he reacts. I don't think he even knows that the request was made to me to see if this could be worked out. I sure appreciate the thoughts shared here. A lot of food for thought. Especially the remark about walking away from this one due to liability.
     
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  4. Shimmy1

    Shimmy1 Senior Member

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    I think this is being over thought. There is no reason you can't put a single line dump valve ahead of the dual acting valve they have now. The only thing they will have to understand is they will need to place the first lever in "raise" to send the oil to the second valve. And, there would probably need to be three different hose connections to prevent mix-ups.
     
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  5. lantraxco

    lantraxco Senior Member

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    You started overthinking it in the first post and the scouts followed you down the rabbit hole. It's okay, I made popcorn :cool:
     
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  6. Willie B

    Willie B Senior Member

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    My one truck has a Heil? dump frame. It has two two stage telescoping cylinders. When I moved it to the present truck, I abandoned the PTO, pump & valve in the old truck. I bought a mated PTO & pump, and used a ordinary two way valve. There is a hose from the tank to the pump, from pump to valve, a low pressure return to tank with the filter.
    Only one hose runs from valve to cylinders, it has a T in it to serve both cylinders. The port that would normally supply the top of the cylinders is plugged. The top of the cylinders are vented to air.
    In my case, the pressure relief valve is part of the control valve.

    In a two way set up, the act of opening the valve to lift opens one hose to pressurized oil, at the same time, it opens the other hose to the filter & tank. Push the valve the other way, it does the opposite, relieving pressure in the other end of the cylinder by sending that oil to the filter. You have to use the valve both ways like a two way cylinder, you only lack one hose.
     
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  7. Shimmy1

    Shimmy1 Senior Member

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    Dump trucks and trucks that pull end dumps use a one line wet kit, sidedumps and other dual acting systems use two.
     
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  8. Tony Wells

    Tony Wells Senior Member

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    Lantraxco, you should know by now I overthink everything. At least the stuff I post here. It's just a bad habit from an anal machinist. Enjoy your popcorn. Hope you brought enough for everyone ;-) And Shimmy1, yes, I tend to be overly analytical with a great many things. And I know it bogs me down. Usually though, if I spill my thoughts here, someone clears away the fog for me and I see the correct solution out of the myriad odd possibilities my mind has cooked up.

    WillieB, I think that is how this particular trailer is set up to operate, only with a single, multistage cylinder. Just pressure in to lift, and a dump valve to lower. Nothing more. It has to be, since there is only a single hose. They drove off with it before I could spend much time with it, so I can't say I traced the hose to see where it went. For all I know there is a pneumatic valve on the trailer that changes everything. I wasn't focusing on the air lines between the truck and trailer other than the normal brake lines.

    Shimmy1, yes, there is a reason I can't just put another valve into this equation. There may be 10 trucks involved. I only have one trailer to rig out to work. All of the other dump trailers, live bottoms, etc, are set up for two hoses. I have been asked if there is a way to make this one trailer operable with any one of the available trucks. I could never convince them, or myself, that spending the time and money to modify all the possible trucks would be justifiable. It would be cheaper and quicker to change this trailer to a double acting cylinder. Then come the liability issues which will prevent me personally from doing that. If it was just changing dump beds from another truck, then sure, change to a suitable valve, no problem and there would be no thread here. I was hoping to just find an easy way to do something safe with the second, un-needed "down" hose. Simple as that. I think that buried in this thread, the answer is here.

    It's the weekend, and Monday I'll talk to the guy who actually owns all this and see what he really wants to do. His ops guy is the one that started all of this while his boss was out of town. I don't work for him, I work for the owner. This started, as I stated earlier, to avoid insp/ins/regis on a trailer that may see only seldom use. It may stop Monday.
     
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  9. Willie B

    Willie B Senior Member

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    No, I don't think you are going to adapt several trucks to operate one different trailer cheaply.
     
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  10. Welder Dave

    Welder Dave Senior Member

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    If most of the trucks have 2 lines maybe you could put a solenoid operated single acting valve on the trailer and run a couple wires to the cab with a switch?
     
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  11. Tony Wells

    Tony Wells Senior Member

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    OK, I got a call from the owner on some other stuff we have going, so I threw this out there. He said we have need to haul 3,000 cords of split bulk firewood per year all year. So he would rather just fix the Mack this dump trailer is already set up for and dedicate it to that job. I think there are 3 customers who want to deal with us that way, so it makes sense to just leave this alone and not mess with playing musical trucks with an odd trailer. One day, should the need disappear, he will just sell this rig as is, set up the way he bought it.

    So, I guess I got suckered by the ops guy (I should have known to just wait and talked to the owner) into trying to figure this out, and got you guys dragged in with me. I apologize. But there are some good ideas and some valid suggestions in this thread and who knows, maybe some drive-by reader will learn something.

    I do appreciate everyone's contribution to this topic, even though it should never have happened. I know you guys all have better things to do than write up stuff on a forum, but also that you guys like to help. And I appreciate it. If you were local, I'd be happy to buy you a beer (if you were a beer drinker of course). But I thank you!

    t
     
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  12. Vetech63

    Vetech63 Senior Member

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    So who won this thread?
     
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  13. Tony Wells

    Tony Wells Senior Member

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    Hard to say, Vetech. I came out ahead in that I don't have to think about it any more, but I lost in that we don't know how to pull it off for sure if it's ever a real need. I think I wasted everyone's time, so I'll take the hit on it overall.

    I think lantaxco is the only one who got to eat some popcorn and was entertained....so maybe he's the winner.
     
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  14. lantraxco

    lantraxco Senior Member

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    Why you won Tony, your first thought was dead right: "My first thought was to just hose back to the reservoir through a check valve on the "down" line."

    Or more simply just disengage the PTO or turn the engine off after dumping so the "Down" line never gets pressurized, the bed would gravity down as it's made to. Worst case with the pump turning you'd be dumping pump flow across the relief until the bed was full down and the control back to neutral. Probably wouldn't hurt a thing.

    I wasn't being critical, there's always many ways to do things, but as one of my superiors liked to tell coworkers, I was the laziest guy in the department if they wanted to know the easiest way to do anything, they should ask me.