While there are various types and designs of pipe benders available this style seems to be  more commonly used than the others.

What this tool is primarily used for:
We use the pipe bender for putting bends into pipe, this is an easy to use machine for bending all manner of steel pipe and up to 180°.

How this tool works:
A hydraulic pump, fitted within the heavy duty steel frame, progressively applies up to 12 tons of pressure. This particular one includes six interchangeable pipe-work formers from ½" to 2" and so should cover all the different pipe sizes you will use. It's relatively lightweight and portable and operates in both horizontal & vertical positions.
Your former, chosen to suit the pipe size, sits on the head of the ram, the two rollers at the top of the frame are then adjusted to determine the radius of bend. Your pipe is slotted under the rollers and into the former and the bend is achieved by pumping on the handle.

Tips for using this tool:
Always mark the centre line of the former, then place a corresponding mark on your pipe, (tipex type correction fluid is ideal). This allows you to re-position your pipe exactly, should you need to tweek your bend.
A homemade angle finder, (two pieces of strap steel bolted together at one end), will help in determining the correct angle to bend to.
Your pipe has an inbuilt memory and will try to straighten out after being bent so a couple of extra pumps on the handle will counter this natural spring effect.

-Tbone