Pre-determined pressure system

A system to apply pressure to an article to be worked on comprising:

• a piston chamber having a piston head slidably mounted therein, a source of fluid, an electrically operated reversing valve means, a first means to supply fluid from said source through said valve means to one side of said piston head, a second means to return fluid from the other side of said piston head to said source, a third means to return fluid from said first means to said source, a fourth means operably associated with said third means to allow fluid from said first means to flow through said third means only when the pressure of the fluid in said first means is at a pre-determined level and an electrical control circuit including a time delay means operably associated with said valve means and having flow switch means for energizing said time delay means responsive to the flow of fluid in said third means past said fourth means as it returns to said source to allow fluid to flow in said first means for a pre-determined time and then reverse the position of said valve means to reverse the flow of fluid to and from said piston head.