At a step of pressurizing a workpiece after reducing a speed of a piston
rod at an end of a forward stroke of the piston rod by restrictively
allowing compressed air to flow out of an exhaust-side pressure chamber,
operation of a rapid exhaust valve is triggered by reduction of internal
pressure of the exhaust-side pressure chamber to lower pressure than
internal pressure of a pressurizing-side pressure chamber to thereby
directly open the exhaust-side pressure chamber into the atmosphere
through the rapid exhaust valve and rapidly reduce back pressure of a main
piston remaining in the exhaust-side pressure chamber.
