Do you have any experience with air casters?

I have a smooth concrete floor and need to create a way to move some big WW machinery (2500 - 3000 lbs). This will be a permanent fixture that will stay under the machine so height is critical.

A pallet jack or any type of machine rollers are out of the question.

Here's what I want to do: Fabricate an air cushion pad using a piece of 1/2" - 3/4" plate steel. Under this plate is a solid rim to hold the weight of the machine in the rest position. Then, when I want to move the machine (to cut long boards etc.), air pressure is applied creating an air caster. This is common practice in industry. One person can move many tons - providing they don't go down a hill.... The overall size of the plate will be about 18" x 40" but the actual working parts of the air caster can be two separate pads located toward each end.

Under the steel plate is some sort of sealing device?, flexible material? or inflatable bladder? which provides a sealing surface to the floor. Any thoughts on exactly how to build this device????

From what I can tell, commercially available air casters are too thick for this application, and they are $$$$..... yikes.

Thanks for any thoughts or suggestions,

Rob