What tells the pump to stop pumping (other than letting go of the rocker switch). Mine are electric and stop on their own when too much force is required, such as in they reached the end of their travel. Could there be a pressure switch that makes the pump stop if the pressure required to move the slide makes think it has hit an obstacle, or do you have a limit switch that tells the pump to stop because the slide is all the way in?
like I said mine are electric but if I have too much weight on the slide then the motor shuts off thinking it's stuck.