Hydraulic Lift Math....

[Badasssapper67]

Anyone have any ideas on books or pdf's about how much a hydraulic cylinder can lift?
What I mean is, if a cylinder can lift 10K lbs but has a 24" stroke and you use it in a scissor lift that lifts 48", does that mean the lift has a 5k lb capacity? Also, to lift more, is it better to go with a cylinder that has a bigger bore, or one that uses higher pressure? Does one with higher pressure mean it's built better and will last longer?

There are a lot of books for sale on the net that are about hydraulics but I was hoping someone here might suggest a good one.

Thanks

 

[pancho400cid]

The force a ram can generate (or withstand) is it's rated pressure times the piston area.

F = P x [(pi x D_piston^2)/4]

The REAL problem is calculating the force that ends up on the ram. There is no simple way to do that, as it is affected by the particular geometry of your lift, vehicle weight and CG, etc. etc. etc.

A scissor lift has more complicated geometry. Conversely, a straight post lift has the vehicle weight fairly in line with the ram(s) axis.

 

[f150skidoo]

You won't know how much it can lift unless you run it through a simulating program. For an example the dump trailer I built has a 3"x24" cylinder with a 1.5" rod diameter. The cylinder can push 21,206 lbs at 3000 psi But with the geometry of everything the cylinder will just lift 6,000 lbs of weight in the bed.

 

[Badasssapper67]

F150- I took a quick look over your trailer build, did you get ready made plans for it or did you design it yourself? My reason for asking is how you decided to locate the hydraulic cylinder.
Also are you happy with the performance of the cylinder and what brand is it?

 

[Badasssapper67]

If you used a simulation program can you tell me what it is called?

 

[J king]

I built my scissor lift. Had an engineer help me on the pressure and the angle that the lift has to overcome.he came pretty close to what the lift needed to easily lift 2 ton.i needed to give the regulator 200 more lbs pressure and it lifted my truck fine.I was impressed with how close it came to his numbers.
He had some kind of formula but I think he had a computer program.

 

[DougWil]

As pointed out a ram's force is simply pressure X area.

For the geometry you want to buy a book on statics.
Older statics textbooks are cheap on ebay.
But of course you need some math skills and a basic understanding of trigonometry to figure out the angles etc..

If you have something specific in mind, draw it up WITH ALL THE DIMENSIONS and post it here and someone can do the math for you.

Also realize that there are losses from pump efficiency and friction that you must account for.

 

[lynnbilodeau]

I was told there would be no math.

 

[Badasssapper67]

J King any chance on posting some pictures and specs? I'd love to see the geometry of the lift. A video would be even better.

 

[Badasssapper67]

DougWil- I need to get an idea of what the best way to go about it is and then I will definitely post it on here.

 

[J king]

Here are a few pics...

 

[J king]

Here is the lock design.click on image for vid.

 

[matt_i]

Its all in a simple formula F = P * A, Force = Pressure * Area.

Run the units for confirmation...lbs = lbs/in^2 * in^2.

Increase the pressure or area (related obviously to diameter) in order to increase force.

The scissor lift geometry has to be analyzed with vectors which isn't hard, it could be done with pencil and paper for a single case, better yet with excel for different heights.

The most difficult condition requiring the most cylinder-rod force will be lifting the scissor vertically when completely closed. The higher the scissor lifts, the more of the load vector of the cylinder is pointing vertically is a simple way to think about it.

 

[J king]

Matt is correct.. The cylinder laying flat to be compact makes it very hard on the cylinder to begin lifting a load. It is the most stress on all components.I have a rocker type hinge that kicked the cylinder up like a pivot. I copied commercial designs.

 

[DougWil]

Matt is correct.. The cylinder laying flat to be compact makes it very hard on the cylinder to begin lifting a load. It is the most stress on all components.I have a rocker type hinge that kicked the cylinder up like a pivot. I copied commercial designs.

Nice work!!

And copying a commercial design, or at least stealing ideas is always a good plan instead of trying to invent the wheel all over again.

 

[the GOAT]

http://www.baumhydraulics.com/calculators/cyl_calc_ang.htm

 

[J king]

Nice link. Thanks

 

[metalmagpie]

Unbelievable the lengths some people will go to in order to avoid doing mathematics.

 

[lakeroadster]

And copying a commercial design, or at least stealing ideas is always a good plan instead of trying to invent the wheel all over again.

And that's how Harbor Freight became what it is today...

 

[pancho400cid]

And that's how Harbor Freight became what it is today...

Too true to be funny....

 

[Badasssapper67]

Awesome!

 

[f150skidoo]

F150- I took a quick look over your trailer build, did you get ready made plans for it or did you design it yourself? My reason for asking is how you decided to locate the hydraulic cylinder.
Also are you happy with the performance of the cylinder and what brand is it?

No plans at all i just built it off the top of my head. The cylinder is a house brand of a store like Northern Tool up here called Princess Auto, its decent for a import cylinder.