Any home type dishwasher fills the lower portion of the tub to a stop point indicated by the float switch. the drive motor in the center operates a pump to force water through the lower [and] upper spray arm. some dishwashers have a rising center sprayer for the upper dish load. I would check the pump assembly for clogging or broken impeller segments. go to www dot partselect dot com to see if you can locate your machine and its exploded diagram.