Deciding on the best method of tipping a dump box

[hydriv]

A friend of mine wishes to build a trailer. The plan is to make it dump hydraulically. The trailer will be towed by his 900 LB garden tractor.

The dimensions of the bed will be 72" long by 42" wide. This will be a flat deck with stake pockets to allow it to be converted to a dump box by adding sides, front and a top-hinged rear tailgate. He wants the load capacity to be for 2000 LBS. Ambitious, I know but better to design for that figure than to build it too light.

I feel that he should be shooting for a dump angle of 55 degrees to make sure sticky soils will exit. Again, I know from my years of tri-axle dump truck experience, there are some loads that will not leave the top corners of the box even with a 90 degree angle but I feel that 55 degrees is much better than 45.

The hydraulic system on the tractor produces 9 GPM @ 0 PSI using 1/2" plumbing and has a relief setting of 2100 PSI plus or minus 50 PSI. The GPM rating is based upon the engine running at 3600 RPM. The control valve is an ON/OFF/ON type with no real feathering, therefore pump output will have to be controlled by engine RPM to avoid having to add another control valve.

I read an old thread on this issue and this site was mentioned to help with the math.

Right-Angled Triangle Calculator

While that is all well and good, it seems that in order to make proper use of that calculator, I would need an understanding of the math itself. I confess that my formal schooling ended after flunking Grade 9 back in 1959 and so far I have managed to scrape by just fine. But even though I have a pretty good understanding of hydraulics, I also recognize my limitations when asked to recommend a suitable hydraulic cylinder diameter and stroke for this application. I respect other people's money and have no desire to waste it out of my own ignorance.

So....it would seem to me that a front-mounted vertical cylinder would not be a good choice for this application. That leaves the following:

1. using two cylinders on an angle that are mounted to the trailer frame on other side

2. a single cylinder on a slight angle mounted to a cross member of the trailer frame and pushing on a re-inforced cross member of the box

3. using some sort of scissors type hoist with a single cylinder.


He intends to use this to haul firewood out of the forest and therefore he will be travelling on rough terrain. There is no intention of having any sort of suspension.


I am open to all suggestions.

 

[J_J]

One example.

http://camsuperline.com/images/trailers/5x8lpdt/5x8lpdt-main.png

Another type

http://premium-supply.com/Images/Products/thumbs/310.jpg

Dual cyl

http://www.johnsontrailerco.com/images/trailer_images/gooseneck-dump-trailer-1.jpg

 

[hydriv]

Yes J_J... those are the 3 methods I was referring to. Obviously, method #1 is preferred because only one cylinder is needed. However, the questions that follow are these.

1 . where on the box should the rod end of the cylinder be anchored?

2. and that question is tied into how much stroke is needed to tilt the bed to 55 degrees?

The longer the stroke, the longer the cylinder and a 72 inch bed length presents challenges that perhaps can only be solved by going to method #2. He is a fabricator so making a simple scissors lift is within his capabilities but if method #1 will work, then why take the hard route?

Granted, there are advantages to the scissor style but this bed is only 42 inches wide and 6 feet long so with a good solid hinge pin, I don't visualize box stability as being a major issue. .

Does it really matter if the cylinder is pushing on the box at 36 inches from the hinge point compared to 30 inches or less from the hinge point? Isn't the force needed the same? Or does leverage come into play here?

 

[J_J]

Use some PVC tubing and play with the stroke length of the cyl and position of the cyl.

Just about any hyd cyl will raise that small bed.

You have to position the cyl so that the bed is down when fully retracted and at the correct tilt angle when fully extended.

You could also so SA cyl or DA cyl.

 

[bcp]

Unless there are reasons not to, build the bed (or sides) a couple of inches wider in the rear to ease dumping.

Bruce

 

[hydriv]

Unless there are reasons not to, build the bed (or sides) a couple of inches wider in the rear to ease dumping.

Bruce

Sorry Bruce. i don't quite comprehend what you are saying. The bed is going to be 42 inches wide. What are you suggesting?

 

[hydriv]

Use some PVC tubing and play with the stroke length of the cyl and position of the cyl.

Just about any hyd cyl will raise that small bed.

You have to position the cyl so that the bed is down when fully retracted and at the correct tilt angle when fully extended.


He will be using a double-acting cylinder because of the size of the reservoir. So, are you saying that he could use a 1 1/2 inch cylinder?


You could also so SA cyl or DA cyl.

Are you saying that where the cylinder pushes on the bed is not critical even though the load may be 2000 LBS?


The closer to the hinge that the attachment point for the cylinder is.... the shorter the stroke.

 

[Ivan49]

How does he plan on stopping it when it is loaded. That is not very big tractor for that much weight. I have a 32 hp tractor weighing roughly 2000 lbs with the loader and my trailer is 5 foot by 10 foot. You don't want to be going down hill when you try to stop. Now back to your question I don't remember how I figured my out when I built it but one thing I do remember is get the angle of the cylinder right. I used a 24 inch stroke 4 inch bore cylinder with a pump similar to what is used on a trailer you buy. It has the resivor on one end > Hooked the clyinder slighly forward of the center of the box and I think the lower ends sets 9 inches below the frame. I have to bring it up by my shop this week and I can measue it if you want. There is a sight on the net that will let you play with the angles and tell you the lift at each angle. I used this and then I did as JJ said on the actual trailer before I welded anything on it . I hope this may help you
One more thing is I would not use it off the tractor hyd system. In my case I have several tractors and each uses a different fluid and I did not want them mixed. I used transmission fluid in my because it works better when the temp is -20

 

[Leejohn]

I would say a 3" cyl. around 28 to 30' stroke dropped down at base end 15deg near the front of trailer. In the front of trailer there more places to mount the base at 15deg. I would also use DA cyl. I have 2 that I made, one has 2 3"cyl DA and I like that better then my small trailer. The small one I used 2 2" SA cyl. and I just like the other one better. My little one is about the size as the one you wanting to make, it's right at 8' long. With the 28 to 30" cyl it give you the 55deg. +.

 

[hydriv]

Ivan.... I do not disagree with your concerns regarding the weight being pulled and the weight of his tractor. However, he is not new to pulling trailers and this one will not be used on steep hills with a full load. Nonetheless, I will caution him because I believe in safety first.

Both of his tractors use the exact same fluid so cross-contamination will not be an issue. Just the same, thank you for mentioning it. If you can find the URL for that site, I'd be much obliged. And if you would measure your trailer and tell me the actual distance between the underside of the box and the mounting point of the cylinder, that would be helpful. I would also be interested in knowing the distance between the hinge pin of the box and the pin that secures the rod end of the cylinder on that 10 foot long box. A 4" diameter cylinder is pretty large and works out to 12.57 square inches x 2000 PSI gives a force of 25,140 pounds of push. That seems to be a lot more than what could possibly be needed for HIS application. Perhaps your pump has a much lower relief valve setting. A 2" diameter cylinder yields 3.14 square inches and with 2000 PSI behind it the force is still 6280 pounds which is 3 times the gross weight of the load and box. There is hardly any cost difference between a 2" and a 2 1/2" cylinder and the 2.5 cylinder yields 4.91 square inches and will deliver 9820 pounds of push.

So it would seem to me that the 2.5 inch cylinder is a better choice on the basis that it would work at a much lower engine RPM and raise the box at a more controllable rate. A lower PSI such as 1000 PSI would still allow that cylinder to push 4910 pounds which is more than double the gross weight of the box and load. And if the box was stubborn in lifting initially, a slight increase in engine speed would produce more volume along with the ability to deliver more pressure.

Does anyone see any flaws in my thinking?


Leejohn - according to the other thread that I read on this site, it is essential to take into consideration the angle of the cylinder at the start of the lift because the push needed at a low angle is much greater than what is needed as the cylinder lifts the box to where the angle is around 90 degrees.