Here is a pneumatic sequence circuit by using a sequence valve.

This is an advenced flash animation ( as far as I am concerned). In this animatione I used Tweening, Masking and Components. As advance as it may be, still there are problems. To test this circuit correctly, make sure the right silindir reaches its destination before you release the green button.

How This circuit works:

Sequence valves are normally closed valves and onl opens when pressure in inlet port reaches at a certain pressure. Assume that highest pressure as 6 bar, we can make sequence valve to open at 5 bar by adjusting spring pressure by sqrew shon on the squence valve.

Air cylinders are fast reacting devices, when a pressure applied they will move their destination very rapidly, smaller the cylinder, faster the movement. To make animation clear, I operated cylinder slowly. In reality slow motion can be accomplished by needle valves and I will prepare a circuit for that soon.
When operator presses green button ( actually when it pushes 5 way valve) right cylinder (clamping) moves forward, to clamp a workpeace. During this movement air pressure on the feeding lines can't reach to full pressure, because right cylinder expanding and only force required is to overcome the friction of the piston. For this reason, there is not enough force to open sequence valve. However as soon as right cylinder reaches workpiece and clamps it, there is no movement and pressure in the feeding line increases. This increased pressure opens the sequence valve and forces top cylinder ( tool cylinder ) begin to edvance forward. Once job is finished, operator can release the green button and both cylinder will retract at the same time.