Hydraulic Cylinder

Carry out a Force Balance: Newton's laws, that sort of thing.

Does it need to push or pull.

F = (1+δ)PA, where F is the force in N, P is the pressure in N/m², and A is the area in m². δ is a margin that allows for acceleration of the load, loss to seal friction, and a "fudge factor".

But, why design one? They sell them. Contact your local sales rep.

And, I didn't point out δ is negative.

A sketch of your application would be appreciated.

How much Pressure is your hydraulic system producing?

What is the range of air temperature? Then you can figure out the viscosity range of your oil.

How fast do you want to move the mass?

How consistent does the speed need to be?

How long are your hydraulic lines? Then you can figure out your line losses.

Is your hydraulic power pack above or below the application?

Have you actually gone to a hydraulic component supplier catalog and looked through their engineering aids? Most of the hydraulic catalogs I've gone through have several pages of help.

Since you obviously know nothing about cylinders and I doubt very much that you could design one anyway, just go to the internet, select a couple of likely victims suppliers and contact them with your question.

It's comforting to know that you have the oil tied down.

These links go from the basics to the formulae required:

http://en.wikipedia.org/wiki/Hydraulic_cylinder

http://science.howstuffworks.com/hydraulic1.htm

http://www.indianafluidpower.com/Formulas.asp#HydraulicCylinderCalculations

http://www.hydraproducts.co.uk/Hydraulic-Calculator.htm

http://www.precisionfluidpower.com/fluid_power_formulas.htm#cylinder

After that you need a good seal catalog:

http://www.gulfcoastseal.com/downloads/eps5370.pdf

Be careful of your material choices since many of the clearances may have issue at temp.

The hydraulic cylinder is only a small part of a fluid power system required to complete this task.

BTY- custom built cylinders are cost prohibitive.

Like my other colleagues have stated, does the application require pushing or pulling the object? Where are you going to place this cylinder? I think the space you supply for it is important. Are you going to attach a nut or something so that it may work?