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Tool Talk Discussion Forum

Hydraulic cylinder placement

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Terry G

02-02-2005 14:06:52




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I want to put a 4"x8" dump bed on a trailer. The cylinders are 38" closed and 68" fully extended. From looking at the drawing, which placement would be the best for the cylinders? Both arrangements will raise the bed to about the same angle when fully extended and will let the bed all the way down when fully closed. What are the advantages of one over the other? Which one will take the least amount of pressure to raise the bed?
Terry G

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Scott Green

02-05-2005 06:07:15




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
Terry , I agree with JHesler. Niether one is very good. My dump trailer is closest to the right drawing. It is rated at 10,000 pounds. Works great! My cylinder is more towards the front of the frame , and more towards the middle of the dump bed. If you would like measurements , just ask(repost).



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JHesler

02-03-2005 11:05:10




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
As far as efectiveness goes, they're both the same. Neither are very good. The best way to do it is with a longer ram and even better is a telescoping ram positioned as far forward on the frame and dump body as possible. If you do use this setup, expect the same results from either way. The only difference is the left one exerts more bending force on the frame and the right one exerts more bending force on the dump body.

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Dave Sherburne, NY

02-03-2005 10:20:56




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
I have actually built one . Mine was like the one
on the Right . Built on a 1972 Chevy 1 ton pickup.
Had a power steering pump under the bed hooked
to the pto from the transmission. Actually the ends of the cylinders [from a John Deere loader] were mounted a little lower than the bottom of the frame of the truck in an attempt to have them
closer to a right angle to the bottom of the box.
Never had a problem dumping a load and it did haul
all the gravel the truck would handle. Actually
I kinda copied it from an article in the MOTHER EARTH NEWS quite a few years ago. Another thing I had about 1 1/2 ' overhang on the frame to put more weight behind the hinge point, So it wouldn't have to lift as much. I think that article is still available somewhere.

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Terry G

02-03-2005 08:57:18




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
Thanks to everyone for all the comments and suggestions. I did the drawings on Autocad and they are drawn to scale. The nice thing about Autocad is you can see exactly what position the bed will be in in realtion to how far the cylinders are extended. The cylinders are fully extended in the top drawings and fully closed in the bottom drawings. I can see now how a long cylinder is harder to use than a short one. I already have the long cylinders is why I was looking at using them. The trailer is so low to the ground there is just no way of putting the cylinders perpendicular to the bed. Scissors hoist or telescopic cylinders are a good idea but seems the best ideas also come with extra $$$. I will do some more looking and may or may not ever build it. It is more of a project than a necessity. As always, a lot of good information on this board.
Terry G

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Paul Janke

02-05-2005 09:43:10




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-03-2005 08:57:18  
One way of getting more of an angle is to move the hinge of the box up or down. I've built a few pickup and trailer hoists. A little math will go a long way in determining if it will or won't work. E-mail me if you want and I can try to help in any way I can.



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steve_ne

02-03-2005 05:56:59




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
Both would more then likely break at the pivot points, pressure needs to go somewhere if not up. Need to angle cylinders in both drawings more. As stated before the drawing on left will have problems with the arc and will not fully extend cylinder. Seen most often is drawing on the right but with cylinders angled and extended below the chaise. The methods of using a scissor hoists or telescoping cylinders. Using long cylinder is very hard to get the angle needed to lift heavy loads. Scissor hoists kits can run you a thousand at supluscenter.com but so can just one telescoping hyd cylinder. Sorry don't mean to squash your idea. Gud luck. I just thought of one more thing. You will need to have some angle at the top of the lift so the weight of the bed will push the hyd fluid out of the cylinder on the way down which left drawing has none.

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BFO

02-02-2005 18:30:21




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
In this instance the model on the left would work. The model on the right, assuming you wouldn't bend the cylinder rod, would jump up violently until the pivot points made it to the over-centre position overcoming the mechanical disadvantage. If you really need to do it this way, place the cylinders so that they are tangental (if that's really a word, who knows I'm justa farmer right? ;-))to the pivot of the dump bed. This would require lowering the cylinder end pivot considerably.
You can buy pre-fabricated scissor hoists for this application, that you can simply weld in place. Just my 2 cents Cnd :-)

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J. Schwiebert

02-02-2005 17:43:24




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
What do you planning on hauling? When we did the cylinder class for dump trucks we had a table of many different materials and what angle you needed to dump them. I think most of them would dump at around 40-42 degrees. If you look at truck hoists we are looking at two styles, The ones with a sissors hoist and the ones with the multi-stage telescopic cylinder. If you went with the telescoping style the cylinder would mount ahead of the bed like a dog house on a dump. Have you looked at any sissors hoist literature

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Mark - IN.

02-02-2005 17:38:27




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
Here's an idea that just may work. There are a lot of manufacturers that mass produce these things for a living, and can probably do a google search on "Dump Trailers" for instance. Take a look at a couple of different models or manufacturers, and chances are will show one while in a tilted position. Chances are that they'll be similar in geometrical positions/angles on the cylinders. You won't get exact measurements from that, but at least you'll get a good idea what a good angle or general placement would be.

Good luck, and make sure that the frame/carriage is strong enough to absorb the force/pressure required. Don't want a Titantic on it's maiden voyage in your driveway, on your foot, or much worse, the wife's flower bed.

Mark.

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Davis In SC

02-02-2005 17:23:35




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
Both designs look to have a huge mechanical disadvantage. All of the force will be on the hinge pivot point when you start to tip the box. The cylinders need to be inclined toward the vertical. You might could mount them outboard with some yokes to mount traveling end of cylinder a ways up the side of box.



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rocker

02-02-2005 17:02:11




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
Gentlemen -

Here's where a little schooling goes a long way. If you take the drawings as a visual reference and don't try to print to an exact scale, it appears that the right drawing shows the clevis' of the cylinder in an almost direct line with the pivot point. A vector analysis of these points being in a line proves that there is no force developed to lift the load regardless of how much oil pressure is put into any bore cylinder. The drawing on the left shows the cylinder in relationship to the pivot point which will give some vector force to lift the load. The direction in which the cylinder is oriented is not important. The critical issue is the amount of vector force developed based on the angle of the cylinder to the pivot point at any given lift distance, most importantly when it is at full down position which is when the cylinder can impart the smallest amount of lift force because of it's shallow angle. Ideally, the cylinder would be positioned perpendicular to the dump bed at the farthest distance from the pivot point of the bed. In short, the bed in the drawing on the right would not be able to move at all (if the points are truly in a line).

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Johnski

02-02-2005 16:59:08




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
The diagram on the left is a perfect example of "Well it looked good on paper". It would require the cyl to travel in an arc greater than 90 degrees or over center. The cyl would stop about halfway up as 90 degrees would be it"s maximum travel. It would actually be retracting past that point if the load carried it over center and would not be able to be lowered. HTH :>( JF



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Lil-Farmer

02-02-2005 17:28:16




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 Re: Hydraulic cylinder placement in reply to Johnski, 02-02-2005 16:59:08  
I would agree, IF it was the bed that was going past 90 degrees. I am assuming the drawings are to scale and represent the cylinder at maximum stroke as drawn. The bed is still leaning forward and will allow the cylinder to continue to extend or cause the cylinder to collapse.



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rocker

02-02-2005 17:24:56




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 Re: Hydraulic cylinder placement in reply to Johnski, 02-02-2005 16:59:08  
Johnski -

The rod end clevis on the cylinder will continue to get farther away from the base clevis of the cylinder until the base clevis, rod end clevis, and bed pivot point are in a straight line. The cylinder will not go "over center" at 90 degrees and be required to retract to continue the dump motion.



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Johnski

02-04-2005 17:10:20




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 Re: Hydraulic cylinder placement in reply to rocker, 02-02-2005 17:24:56  
I still say that the drawing on the left will not work. I got my numbers a little off but here's how I see it. The rod end of the cyl does not travel in a straight line but in an arc from the retracted position to the raised position. Halfway through it's travel would be the peak of the arc(about 45 not 90 degrees). Past that point the cyl would actually be required to shorten in length to reach the point shown. Print out the pic and scribe an arc to see what I mean. I'm no engineer but have been working on trucks and equipt for 30+ years and have never seen a cyl have a swing with that much travel. One other option would be to mount the cyls near vertical on each side of the bed like the newer off-road dumps.

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Rod (NH)

02-02-2005 16:21:00




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
Hi Terry,

Well, you're getting a variety of opinions but I believe Lil-Farmer is correct. The left one is the better choice. The one on the right has very little moment arm about the bed pivot point to begin raising the load. That's the worst condition - to begin the lift. In fact, the cylinder thrust appears almost in line with the bed pivot point. That would mean that there would be no lift at all, no matter the cylinder force and something would break rather than lift.

third party image Rod

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sibby(Aus)

02-02-2005 15:05:47




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
I agree with lil farmer, one on left has far more leverage.



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Jet9N

02-02-2005 15:38:42




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 Re: Hydraulic cylinder placement in reply to sibby(Aus), 02-02-2005 15:05:47  
I to agree with lil' farmer too. If you draw a triangle by drawing a line from pin to pin, the trangle at left has a higher altitude.

Jet



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old

02-02-2005 14:54:40




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
I think the one on the right would work best because it doesn't fight the frame as much. Also it looks more like the way most factory beds that I have seen work.



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Lil-Farmer

02-02-2005 14:30:43




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 Re: Hydraulic cylinder placement in reply to Terry G, 02-02-2005 14:06:52  
The one on the left would have the most advantage. The cylinder would have the most leverage on the lift point and would require the least amount of pressure to start the load when the load is greatest. You are also lifting about 2/3 of the way towards the front of the load which will decrease the the requirements for stiffness in the frame of the box.



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ken hortman

02-02-2005 16:06:06




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 Right is best ! in reply to Lil-Farmer, 02-02-2005 14:30:43  
From a engineering stand point the one on the left is going to travel to far and will not stop as you have it drawn, it will not stop on it own and will go past straight up and down as you show, which will not allow it to lower. The only way to go is like the drawing to the right.



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