The hydraulic press in figure 10-10 contains a valve. As the small piston moves down, it forces the fluid past check valve A into the large cylinder. The pressure of the fluid on the check valve spring below the large piston helps force that valve shut. The liquid that has passed through the valve opening on the down stroke of the small piston is trapped in the large cylinder. The small piston rises on the upstroke until its bottom passes the opening to the fluid reservoir.
More fluid is sucked past check valve B and into the small cylinder.
The next downstroke forces this new charge of fluid out of the small cylinder past the check valve into the large cylinder. This process repeats stroke by stroke until enough fluid has been forced into the large cylinder to raise the large piston the required distance of 1 foot. The force has been applied through a distance of 10 feet on the pump handle. However, it was done through a series of relatively short strokes, the total of the strokes being equal to 10 feet. Maybe you re beginning to wonder how the large piston gets back down after the process is finished.