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Dump Cylinder Plumbing Pics

Effinay

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IMG_3840.jpgIMG_3839.jpgIMG_3841.jpg
These are pics of the cylinder I'm trying to use, and the type of valve arrangement that is on the truck....
Hope these will clarify what I'm up to, and thanks for the input and suggestions.....
 

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lantraxco

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That cylinder is what I guessed it was from your description, old style one way pressure up and gravity down setup. The low pressure line from the rod end was connected to the PTO pump suction and as the cylinder goes up the oil feeds from there through the pump and valve to the piston end of the cylinder. As the hoist is lowered the oil flows back from the piston end through the valve to the upper end of the cylinder in the original system.

I can see in your valve stack you have some sections with a single work port, these would seem to be designed for single acting cylinders. Like I said you can just connect one work port to the piston end of your dump cylinder and the other work port can be teed into a tank return line if you're using a section with two work ports, it will work.

I'm thinking you need to repack that piston on this cylinder, but you might make sure you have pressure on the hose first, you could cap the hose to the butt end of the cylinder and gently engage the hoist valve, you can hear it load up and maybe the relief pop open if the valve is working correctly. You know you have pressure on the line going to the top of the cylinder as you say it blew off?

That's a pretty big cylinder probably designed for a fairly low pressure you might consider adding a relief valve between the valve stack and the cylinder, though I can't advise you on the correct pressure setting. Maybe start at 1,000 psi and if needed work up from there?
 

Effinay

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Thanks for the response... I think I'm starting to get a grasp on how this needs to work, but I'm still a little fuzzy on a couple things. Thanks for your patience and sharing your knowledge, and here goes: I need to attach one line from my valve stack to the "inlet" on my cylinder which will provide pressure to extend the cylinder and raise the body. I also need to provide a line from the unused port on that same valve to a return line to the tank. In a previous post you suggested to tee the 1-1/4" line to another return line to the tank. By operating the valve to introduce pressurized oil to the cylinder I'll be able to raise the body. When I let the valve return to the "neutral" position, the body should hold in that position? Or will it drop because there is nothing to keep the oil in the cylinder? "Return"(1-1/4") plumbed directly to the tank return......
 

lantraxco

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If the valve you are connecting to is a normal cylinder spool for a double acting cylinder it will lift the body in one direction, hold the oil when in neutral, and as you move the spool in the opposite direction it will lower the body. If by some chance it was designed with a motor spool then it won't hold, but that's probably not likely.

The low pressure line from the top of the cylinder will now be just a leakoff line, it can go to the tank anywhere.
 

Delmer

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I don't think you want fluid in the top part of that cylinder, so keep the return line above the oil level. Also, I'm don't see why the piston seals would be leaking? You'll know when it's hooked up right, if it's leaking then the bed will drop. You could hook up the return run to a bucket and lift the bed the way you have it and let it sit to see if it drops and/or oil continues to come out the top of the cylinder.

Also, if it's only air in the top of the cylinder, then a half inch line is plenty big.
 
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Effinay

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Thanks again Lantraxco and much obliged from Delmer as well.....I went back to the cave and scratched this out on the wall.....Does this look right?
 

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lantraxco

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That's the basic idea, but as Delmer said it would be better if the line from the rod end of your cylinder can be connected to your tank above the oil level, so it only returns whatever internal leakage there is. As you have it drawn now it may work but you will have oil flowing back and forth every time the cylinder extends and retracts which is probably unnecessary and may cause some leakage around the rod seals.

On that lower picture the bottom hose, your arrows are actually backwards, if the rod is moving in, the oil would be flowing from the tank to the top end of the cylinder?
 
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