OK, there probably is a simple answer here, but the coffee is not working yet. I got asked by a customer yesterday about using a dump trailer with a single acting cylinder on a tractor with a pump and valve setup normally they use with a dump trailer with a double acting cylinder. I figured it's possible so I told them "probably". Then I started thinking about it and knowing what I do in general about hydraulics, I began to wonder about the valving specific to the tractors using double acting cylinders. Don't they simply vent the non-pressured end of the cylinder back to the reservoir when moving? If I try to provide a way to do this, I have to make it idiot proof and make it impossible to connect wrong when they want to use either kind of trailer. My first thought was to just hose back to the reservoir through a check valve on the "down" line. But that assumes the valve handles the release of the "up" side pressure. Never looked all that closely at the system. Thoughts anyone? Going to go take a look at the first truck they want to attempt this with. It's a Volvo of some model. This idea is all to prevent registration, inspection, and insurance on a single tractor that already has a setup for a single acting cylinder dump trailer. They say this trailer will only be used once in a while. If it were mine, I'd probably just change to a double acting cylinder and be done with it. But it's their money.
My personal opinion is.....I wouldn’t touch it. Too much risk of trusting a customer saying “ it would only get used once in a while”, and modified trailer leaves you with liability if an accident does happen.
Yeah, I kind of feel that way too. This is a life-safety thing. I really try to avoid getting into too much on those projects. I'll generally repair something like that, but modifications are out of bounds. I just figured there was some simple way to connect this single acting cylinder trailer to a "normal" (to them anyway) tractor with connections for a double acting cylinder.
Just went through it on a dump truck. Upper end of the cylinder gets vented to atmosphere. lower end goes to one port of a two way valve, when releasing it lets oil through the valve to the tank port exactly as it would in a double acting cylinder.
So Willie, do you just let the the hose normally connected to the upper end of the cylinder dangle? There are of course dry break connections on the lines.
I guess I’m just concerned about what happens in the valve if they push it to “lower”. Will it deadhead and dump through the relief valve or something more insidious. I can’t risk a blown hose or exploded pump. There has to be something that dumps pressure at the end of stroke anyway but I wouldn’t think it would tolerate being used as a dump path. Of course, that shouldn’t happen often when the driver understands that it could cause overheating but how else does the pressure get relieved when lowering the bed? The regular valve has a specific path for each direction but that requires both hoses I think. I’ll have to look at the truck they want to use. Sounds simple but I think there are rocks just under the surface of this smooth water.
No expert, but sounds to me like the same setup as my hydraulic dump truck with one line The valve moves full back sends high pressure in thru on end and the cylinder is extended. Valve placed in the middle stops flow and does not allow fluid to come out. Move to full forward fluid comes back out same line which returns it to the tank
Yeah but if that’s an original setup with a valve selected to operate a single acting cylinder that’s what I would expect. My question is about positioning the valve lever “down”, which would pressurize the second hose that normally would go to the top port on the cylinder. Since even single acting cylinders have both holes usually, I wonder what would happen if it were plumbed as though it was a double acting cylinder. I’m sure the piston seals and end cap packings would be different but guess I cannot say for certainty in this particular case.
I think the other end is left open with a filter to keep dirt out something like this http://www.classicrefusetrucks.com/albums/GW/GW01.html There is also one which uses another line which goes back to the tank
Just thinking out loud, but could place a diverter valve in the orange line above to send fluid back to another cylinder on the trailer. Then use the same lift valve to operate it
I’ve seen those vents used on Somme cylinders. That be be all that’s required. If not for needing to avoid modifying the truck to match this single, oddball trailer I could rework the plumbing to make it work, but of course there are several tractors they may want to pull this trailer with so I can’t just change this or that tractor to suit this trailer and dedicate a matched set. That I have now but nobody wants to do all the legal stuff on this tractor which won’t be able to pull any of the other two hose trailers.
Could you just run the other hose back to the reservoir? Sorry I replied before I read the last post. Thanks
That was the first thing I thought of. Running it back through a check valve to the reservoir. But then I started thinking about all the other tractors they will need to pull it with, so it got complicated from the logistics angle more than the mechanics of making it work and making it idiot proof.
Key function, Idiot Proof, Don't Happen usually.
If you could find out what is on it for a wet line kit that'd be a help. We have a few trucks that haul both trailers with single and double acting cylinders. For the dump trailer only the pressure line gets hooked up. They turn on the PTO, and use the control to raise. I think there's position for raise, hold, and down, down vents back through the same line. For double acting hydraulics, the return line gets connected, the control gets set in the raise position, and it circulates through a valve on the trailer, and you actuate the levers back on the trailer. Pretty sure they are Muncie setups with a piston pump and a hi/lo pressure valve.
No. A cylinder built for another purpose (a double acting cylinder ) is plumbed as it should be. Yes, it works as any other would, as you fill one end, the content of the other end passes through the valve to return to the tank. Dump cylinders are usually one way, no power down
Have seen single line wet kits with multi line pumps, one that used to be on my KW was that way so could run a live bottom or a single line.
I’ll have to check into that. Naturally this got more involved than I hoped. I just figured there was something simple I wasn’t seeing that would let me just make a single connection on the dead end of the cylinder and have it dump down back through the control valve. But then I began to wonder about the valve trying to pressurize the top of the cylinder on that type system with that line basically blocked off. I don’t like sound of that. It might be that I could machine a lockout mechanism to allow a pin to prevent the lever from being moved into that position. I think our drivers (we have 4 I believe) could handle that. That approach would be simple and easy so they could grasp it. As long as they were locked out of a lever position that would jeopardize the system, I think I could deal with it. If they fail it’s on them. Even if they did fail to put the limit pin in place, and inadvertently actuate the valve the wrong direction, the relief valve should save the equipment. If I went that route, I think it could be whittled down to 3 tractors that would need this modification.
I have two trucks set up that can run either single line or double line wet kits. I have a "dump truck" style pump, that would be typical for a single line dump trailer or a dump bed on a tandem. They return oil to tank, right at the pump when they are in the "lower" position on the cab valve. I then have a second hose, that you can hook up when running a two line lowboy or such trailer. That second line returns directly back to tank. You can't hook it up wrong, I have a larger line and smaller line, with different size fittings. The delivery is the same size on all your "pressure" lines (lowboy or single line dump), and the return is a different size. On a dump trailer you only hook up the one line, on a two line you hook up both. I have a standard control in the cab that is used for single line trailer. Raise - hold- lower. To run a two line trailer, you just move the lever to "raise" in the cab, and that starts the flow. It returns through the second line. You don't need anything complicated, just dump truck/ trailer style pumps that can flow, and return to tank right from the pump.
A two way system (power up, power down) gets a valve connected to pump & tank. If you use a two way cylinder, it works fine. When the valve pushes oil at the butt end of the cylinder, it releases under low pressure from the other end of the cylinder to the tank. A one way cylinder just doesn't send the oil from the top to the tank.
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.
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.
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.
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.
You started overthinking it in the first post and the scouts followed you down the rabbit hole. It's okay, I made popcorn
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.
Dump trucks and trucks that pull end dumps use a one line wet kit, sidedumps and other dual acting systems use two.
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.
No, I don't think you are going to adapt several trucks to operate one different trailer cheaply.
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?
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
So who won this thread?
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.
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.