How Do You Calculate the Force Needed to Dump a Load?

Missing information:

• The vertical distance between the fixed end of the cylinder and the hinge
• The vertical distance between the pivot end of the cylinder and the hinge
• The diameter of the piston in the cylinder
• The distribution of the load upon the dump table
• The horizontal position of the hinge relative to the dump table floor
• The weight of the dump table structure, cylinder, piston and its tail-rod.
• The centre-of-gravity of the dump table, cylinder, piston and tail rod and its horizontal and vertical distances to the hinge.

PW, thanks for the help, here it is

The vertical distance between the fixed end of the cylinder and the hinge

4.75 - 2.00 = 2.75"

The vertical distance between the pivot end of the cylinder and the hinge

OK, that was missing it's 3.75" when the cylinder is down.

The diameter of the piston in the cylinder

That is to be determined when we know the required force to dump the load. I have some design leeway to change the opening.

The distribution of the load upon the dump table

Mostly in the center, but the customer may load the bed anyway they want.

The horizontal position of the hinge relative to the dump table floor

Not sure I understand the question.. It's 4.75" from the bed and there two of them, one on each side of the bed, but only one cylinder, it's located in the middle of the bed.

The weight of the dump table structure, cylinder, piston and its tail-rod.

Total weight includes the weight of the bed. The cylinder weight can be what ever we need to dump the load. They average around 60#

• The centre-of-gravity of the dump table, cylinder, piston and tail rod and its horizontal and vertical distances to the hinge. The center of gravity (without the load) should be in the center of the bed, The bed has two hinges, one on each side of the bed, but one cylinder exactly in the center of the bed.

<The diameter of the piston in the cylinder "That is to be determined when we know the required force to dump the load. I have some design leeway to change the opening.">

Then the pressure cannot be determined, as the pressure required is the force required divided by the area of the piston!

PW,

Again thank you for the help. I have a hydraulic cylinder but I want to change it to a ball screw or some electric cylinder. When I search ball screws on-line they all quote the force they can produce, so now I'm looking for a little help in figuring out what size to select.

Laby

If you measure the maximum pressure going to the cylinder under load (I think it will be just before the piston starts to move), and measure the diameter of the (threaded?) piston retaining ring. The pressure (psi) times the area (pi*D*D/4) times a safety factor (something greater than one) will tell you what you want to know.

Do you know what the normal working pressure of the currently installed cylinder? If you know that, just replace it with a similarly rated component.

It looks like the load will be dumped to the right(in reference to the sketch)...Where the cylinder is attached to the "bed", it would take more force to lift the "bed" due to it being so close to the hinge(fulcrum). I don't know the extent that this is used, but it seems like a waste of energy not utilizing the mechanical advantage(MA) of the "lever". The only thing I could think of is that there is no room for a longer cylinder that would achieve the same height being connected to the far left(higher MA) - such as a dump truck.

The following link is to a pdf file which can give you some formulas that may help.

http://www.hydraulicsupermarket.com/upload/db_documents_doc_5.pdf

Taken from this site

http://www.hydraulicsupermarket.com/technical.html

The original engineer that spec'd this out never did any calculations, and he said he doesn't know the max force the cylinder is capable of, our only known here is that the hydraulic system puts out 1,500 psi max.

The original engineer that spec'd this out never did any calculations, and he said he doesn't know the max force the cylinder is capable of,...

Then your "original engineer" was not an engineer. You would be foolish to allow this thing to operate near personnel, without its having been engineered. You'd be leaving yourself open to lawsuits you'd have no chance of winning.

If you wanted to calculate the effective leverage at its most disadvantageous point (which is with the load down) then a very simple way is to raise the load CG by precisely 2" and measure the extension of the cylinder to achieve that. Given that there is no way of knowing when this thing is going to break, I would not place any part of my body under the load (to measure cylinder extension) without being certain the device is securely blocked. If you failed to take adequate lockout tagout precautions in doing these measurements, OSHA would be justified in levying very heavy fines.

Even at 2" lift, the leverage will have changed from the fully down position, but it will get you in the ball park. Just from looking at the drawing without doing any calculating (because a couple key measurements are missing) it appears that the leverage is very disadvantageous: 10:1 one in favor of the load vs the cylinder?? (There is no way of knowing without knowing the horizontal distance from the load CG to the hinge center.) So if we guess that the force required is 25,000 lb, then we'd divide that by 1500 psi to get the cylinder area. But it sounds like you are thinking about an electric ball screw actuator -- in which case, you'd be thinking of something of about 25,000# thrust... IF my guesses are in the right ball park. But those guess are just that -- the key dimensions are not on the drawing.

Any engineer would be certifiably insane to spec this without a full drawing set. Are the cylinder mounting points adequate? Is the frame as a whole adequate? Are we certain the entire thing won't tilt if the load sticks at the dump point? If this is going to a customer, where it will not be under your immediate control, then adequate engineering becomes all the more important. I wouldn't release something like this without having an engineer doing the analysis -- and that is not something that can be done remotely without a full and accurate drawing set signed off by a company rep with the authority to commit your company to potential multi-million dollar liability claims if the engineering is faulty.

I think you should hire a real engineer. The forces involved here can and do kill people.

Thanks Arctic, this will be very useful and I've stored in my hard drive for future reference.

Question to the room:

If I do as Arctic suggest, and reverse engineer it, I could for example, spec out a 15,000 psi cylinder at a cost of ... say $1,000 a pop, when in reality, I did the math, if I knew how, it would show that I needed say 3,000 psi at ... say $100 a pop. As you can see, by my thinking, just reverse engineering is not a cost effective way to solve a problem.

FYI - the title had me rolling with laughter......

There is no confirmed proof that the life is serious.

I was thinking the same thing I suppose...maybe measuring the height of the vane popping out of your forhead?

Me too -- I wondered if this was a question about diverticulitis.

Ditto. Hard to believe that Kris, and Dell both left it alone.

There is an entire weekend ahead Bob. We pace ourselves, but this does look mighty attractive !

Ok to start: the max for on the existing cylinder is simply the system pressure X the pushing area of the cylinder. Remember that when the cylinder pulls the area is decreased b/c of the rod.

Also the max force is need when the table is in its starting position. You can use pathagriums (sp) therum (i'm an engineer not a speller) to find the vertical force that the cylinder can produce with a given hypotonus (max force calc'd earlier). Then use similar math to see how the much the table can dump with the rod and pivot point being farthest away (fully closed).

I hope my inability to master my own language didn't completly destroy my response.

For the amount of force to actually 'dump a load' I think we're missing some info. Densiy of the 'load' elasticity of the orifice, pushing area, and daily fiber intake.

The dump force is calculated by taking the moments about the hinge point which can't be done with the information given in the original question. To this answer you apply a safety factor and make sure all your components are capable of taking this force.

There much more theories to argue between engineers and no one works!

To answer your question if the sketch is correct than the required force can be as high as 15000...18000 lbs. It all depends on the dimensions you gave and those you did not give and I estimated.

To dtermine the necessary force you should consider the worse position which is the lifting start when the table is horizontal.

You try to find all dimensions in order to compute the resistent torque taking the hinge as a reference. You consider a loss depending on the bearings from 5 to 15% and compute the force considering the level arm length as a perpendicular from the hinge center to the cylinder center line direction.

I give you those details since it seems to me that you are in an non engineering environment according to the fact that the "engineer" did not make any calculation.

To determine the boggest length arm of the load you should condider its "density" since you cannot consider the load as concentrated.

Hope it will help.