Need help to determine bore size of hydraulic cylinder

[rmccullars]

I am building a lifting device using a hydraulic cylinder to produce an 8 ft lift, of a load approximately 2,000 pounds. The speed of the lift is also very important. I need to raise the load 8 ft in 8 seconds. I have a 15 hp hydraulic pump with a 30 gal tank available for this task. I have designed the "elbow linkage" that will give me the mechanical movement, but my hydraulic supplier doesn't feel comfortable specifying the cylinder bore size required to lift the load.

Thanks in advance for any assistance.

 

[hydromech]

2000 lbs is not a lot. Working within the parameters you have set, the cylinder bore size is going to be quite small. Therefore, with a stroke of +8ft the rod could buckle if the load is not rigidly guided.

The rod could be beefed up a bit, but that depends on how you intend to get the load back down again. Will the load be allowed to fall under gravity...or will it need to be forced down by the cylinder?

If the rod has to be thicker, the bore may have to increase if you need a large annulus area to push the cylinder back down.

Increasing the bore size will slow the cylinder speed down as you only have a limited amount of power.

Pneumatics may be better...

A cylinder with a bore dia of 1.5" will lift 3762 lbs @ 2175 PSI
7.9 GPM will lift the load in 5.54 seconds.
7.9 GPM @ 2175 PSI = 11.82 HP
The volume of the cylinder bore would be 0.713 US GAL'S

Give us some feedback...then we can get a bit closer to the solution.

Regards

Hydromech
Hydraulic Systems Engineer

 

[budt]

Need to know more about the "Elbow Linkage" you have designed also. If it gives added travel distance, as you seem to indicate it would shorten the cylinder stroke but require more force than a direct coupled cylinder.

Have you looked at a junk yard for a Fork Lift circuit that uses a chain to double the load travel?

Not enough info.



Bud Trinkel CFPE
HYDRA-PNEU CONSULTING, INC.
fluidpower1 @ hotmail.com

http://www.fluidpower1.us

 

[juzboarder]

I agree a hydraulic cylinder wouldn't be ideal, try pneumatics if possible.

JB

 

[PNachtwey]

"Pneumatics may be better..."

I don't think so. It would be very difficult to control unless the load is going to a hard stop. Hydromech, I a think model of this would be educational. I think the system would oscillate wildly until it is up agains the stop. Calculate the natural frequency. It will be very low. Given that the system must acclerate relatively quickly compared to the natural frequency it will oscillate as it moves.

How would one calculate the natural frequency?
What is the bulk modulus of air?

This would be easy to control with hydraulics. My instincts tell me that pneumatics would not work smoothly.

 

[hydromech]

I replied to the original post directly, against the rules I know, it was just easier...

The elbow linkages were a mechanism that were fixed top and bottom with a pivot points in the middle.

The cylinder would be attached to each of the "elbows", as the cylinder extended, the pivot points were push away from each other forcing the lower part of the mechanism to rise.

From the first post it appeared as though the best solution would have been pneumatic because of the low forces.

With the elbow linkages the force is amplified and non linear so to play it safe I produced a 3D working model of the assembly and sent rmccullars this mail.
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Ron,

Have a look at the attached video. I believe that is what you are trying to do. I have modelled the assembly and moved the cylinder position cylinder as close to the top pivot points as possible. Basically, the closer the cylinder is to the top pivot points. the higher the required cylinder force.

Because the cylinder is at 90 degrees to the direction of movement of the load, the forces required to start the load moving are very big...probably more than 4000lbs. The closer the cylinder is to the top pivot point, the more leverage is placed on the cylinder...thus the more force required to move the load.

The forces at work within the structure will necessitate heavy fabrications, this will again cause the load on the cylinder to increase.

It is not an easy calculation because the load changes are non-linear.

As a duty cycle 3 op's per minute is Ok, but if the machine will run for longer than about half an hour you will need a bigger reservoir or a cooler.

A 2" cylinder will give 6748 Lbs @ 2175 PSI. The cylinder will stroke fully in 5.56 seconds with a flow of 5.28 U.S GPM. The power required to drive this would be 7.77 HP. You can install some controls to limit the force if you need to. Its better to have more than you need anyway.

It seems that you have enough power to get what you need. The rod size on the cylinder would be 1 1/2". If you can keep the rod at 1 1/2" to avoid buckling.

Let me know if you need more help...sorry I can't give a precise calculation.

Also let me know if the model is any use to you, I can adjust it to suit or mail more videos to you.

Regards

Adrian
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then got this reply
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Adrian,

God bless you. I can't tell you how much I appreciate your assistance. Your model is right on the money with regard to design concept. Your comments are also in line with those of my hydraulics supplier.

I believe that with you model and comments I can move forward with the fabrication of the lift with a higher level of confidence. Of course I will build in a hugh safety factor just to protect the workers around the machine, not to mention my own liability.

Again, I can't express my sincere thanks for your help. If I can ever return the favor, please do not hesitate to contact me. I am a mechanical engineer with over 30 years experience in material handling design and fabrication, but very limited exposure to hydraulics. But if I can help you with anything please let me know. I would be honored to lend my expertise any time.

Sincerely,

Ron McCullars