Dump Trailer - Scissors Hoist - Plans?

   / Dump Trailer - Scissors Hoist - Plans? #11  
Speaking of dump trailers, mine (7K) is a scissors lift, however like many of them it is a bit underpowered when I may have too much of a weight towards the front of the trailer. I was thinking of adding a small single stage hydraulic cylinder in the front working off the same line the big cylinder is being fed to assist in lifting. Does anyone see any problems with that? The small cylinder would only go up about 12", then be free of the dump.

I'm glad you brought this"helper"cyl up Pete. I believe as you do that the first few inches are far more taxing on the cyl in sissors configuration. I also have pictured the added cyl pushing until extended then loosing contact with bed until bed is lowered. I have wondered about the necessary modifications to use existing pump to power the add on cyl. If this sound's interesting to OP,I'd like everyone to help explore this farther. In building a new trailer,the attraction is saving cost of large cyl by incorporating 2 less expensive cylinders. Here's my most perplexing issue. Must added cyl be rated at or above pump capability? Will added cyl suffer from continued pressure after reaching max extension while sissors cyl continue's doing it's job?
 
   / Dump Trailer - Scissors Hoist - Plans? #12  
I'm glad you brought this"helper"cyl up Pete. I believe as you do that the first few inches are far more taxing on the cyl in sissors configuration. I also have pictured the added cyl pushing until extended then loosing contact with bed until bed is lowered. I have wondered about the necessary modifications to use existing pump to power the add on cyl. If this sound's interesting to OP,I'd like everyone to help explore this farther. In building a new trailer,the attraction is saving cost of large cyl by incorporating 2 less expensive cylinders. Here's my most perplexing issue. Must added cyl be rated at or above pump capability? Will added cyl suffer from continued pressure after reaching max extension while sissors cyl continue's doing it's job?
If you tee the second cylinder with the primary cylinder the oil will flow the path of least resistance which would be the vertical "assist" cylinder until it tops out. Then the oil would all go to the scissor lift. You'd have to make sure the reservoir on your pump holds enough oil to fill both cylinders.

One possibility to consider...if you were dumping down hill and the load sticks to the point of taking the bed's center of gravity aft of it's hinge point, it could suck the oil out of the assist cylinder and slam the bed all the way "up" and possibly bend something.

A situation something like this:
AFV Dump truck tips - YouTube
 
   / Dump Trailer - Scissors Hoist - Plans? #13  
If you tee the second cylinder with the primary cylinder the oil will flow the path of least resistance which would be the vertical "assist" cylinder until it tops out. Then the oil would all go to the scissor lift.Perfect,just what I want You'd have to make sure the reservoir on your pump holds enough oil to fill both cylinders.Should be simple to accomplish.

One possibility to consider...if you were dumping down hill and the load sticks to the point of taking the bed's center of gravity aft of it's hinge point, it could suck the oil out of the assist cylinder I don't understand and slam the bed all the way "up" and possibly bend something.

A situation something like this:
AFV Dump truck tips - YouTube
I'm not understanding why the assist cylinder would/could worsen the risk of doing this.
 
   / Dump Trailer - Scissors Hoist - Plans? #14  
If you tee the second cylinder with the primary cylinder the oil will flow the path of least resistance which would be the vertical "assist" cylinder until it tops out. Then the oil would all go to the scissor lift. You'd have to make sure the reservoir on your pump holds enough oil to fill both cylinders.

One possibility to consider...if you were dumping down hill and the load sticks to the point of taking the bed's center of gravity aft of it's hinge point, it could suck the oil out of the assist cylinder and slam the bed all the way "up" and possibly bend something.

A situation something like this:
AFV Dump truck tips - YouTube

This will be a winter project. I did mount a little 4 ton hydraulic jack to one side to lift the front about 8". That was enough to let the main cylinder take over and do the job it was supposed to do. I had to be careful not to twist the bed using the small jack on the one side. This seems to be a common problem with these dump trailers, especially if the load is situated to far forward. Trying to load the trailer more towards the rear to make the dumping easier also sometimes makes the towing very unbalanced. If I get this done I'll post the results. If anyone else tries this, I hope you'll do the same.
 
   / Dump Trailer - Scissors Hoist - Plans? #15  
This will be a winter project. I did mount a little 4 ton hydraulic jack to one side to lift the front about 8". That was enough to let the main cylinder take over and do the job it was supposed to do. I had to be careful not to twist the bed using the small jack on the one side. This seems to be a common problem with these dump trailers, especially if the load is situated to far forward. Trying to load the trailer more towards the rear to make the dumping easier also sometimes makes the towing very unbalanced. If I get this done I'll post the results. If anyone else tries this, I hope you'll do the same.

Make's towing dangerous to say the least.
 
   / Dump Trailer - Scissors Hoist - Plans? #16  
This will be a winter project. I did mount a little 4 ton hydraulic jack to one side to lift the front about 8". That was enough to let the main cylinder take over and do the job it was supposed to do. I had to be careful not to twist the bed using the small jack on the one side. This seems to be a common problem with these dump trailers, especially if the load is situated to far forward. Trying to load the trailer more towards the rear to make the dumping easier also sometimes makes the towing very unbalanced. If I get this done I'll post the results. If anyone else tries this, I hope you'll do the same.

It looks to me like he forgot to unlatch the tailgate. I'm not sure what the dumping mechanism has to do with it.
 
   / Dump Trailer - Scissors Hoist - Plans? #17  
The video was just an extreme example of an instance where the center of gravity of the dump bed shifted so far back that it flipped the truck. If you had a 12" "lift assist" cylinder tee'd into the main cylinder, it would allow the dump bed to "free wheel" up and bang against whatever stop you have at the end of the scissor lift travel rather than gently top out under pump pressure.

Maybe a sequence valve would prevent that behavior, I've never messed with one though.
 
   / Dump Trailer - Scissors Hoist - Plans? #18  
If you tee the second cylinder with the primary cylinder the oil will flow the path of least resistance which would be the vertical "assist" cylinder until it tops out. Then the oil would all go to the scissor lift. You'd have to make sure the reservoir on your pump holds enough oil to fill both cylinders.

One possibility to consider...if you were dumping down hill and the load sticks to the point of taking the bed's center of gravity aft of it's hinge point, it could suck the oil out of the assist cylinder and slam the bed all the way "up" and possibly bend something.

A situation something like this:
AFV Dump truck tips - YouTube

I've thought about this for a while. I don't think you are making a valid point. (Though it's definatly worth thinking about) A scissors type hoist has a dual acting cylinder. It has pressure on both side of the piston. If you T the lift assist onto the lift side of the main cylinder and just use the lift assist as a single acting cylinder it'll work. The load will never take off as the main cylinder still has oil on the down side of the cylinder. If you T the lift assist into both sides of the main cylinder then there is a possibility that it can take off but only as far as the volume of oil inside the lift assist cylinder will let it.

Just to try and clarify what I'm describing here. The main scissor lift cylinder is a double acting cylinder and the lift assist is working as a single acting cylinder.

After thinking about this overnight I'm going to say that you are partially right. The load will take off if it over centers. You can control the load by releasing the hydraulic lever on the tractor. The effect of the volume of oil in the lift cylinder would be lessened with a restrictor installed in the hydraulic oil line going to the single acting cylinder
 
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   / Dump Trailer - Scissors Hoist - Plans? #19  
I'm also interested in this post, I'm commenting so I can follow.
 
   / Dump Trailer - Scissors Hoist - Plans? #20  
You're right that a double acting cylinder would be less prone. The only scissor lifts I have worked on were in dump bed inserts we used to install in pickup trucks. They had an electric pump and a single acting cylinder which is what I had in mind.
 
 
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