Dump trailer hydraulics. General question.

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.

Tony Wells said:

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.

Click to expand...

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.