As the pump rod is raised, a vacuum starts to form below the plunger allowing atmospheric pressure acting on the cistern to force water from the cistern up through the clack valve and into the pump. On the down stroke of the rod, the weight of water in the pump instantly forces the clack valve shut preventing the water from falling back into the cistern and with only one route left the water is forced through the second valve and up the rising main. As the pump rod commences the upstroke,  the weight of water, this time in the rising main falls onto the second valve forcing it closed thus retaining the pumped water in the rising main whilst at the same time, water is again drawn into the pump from the cistern. As all the pumps were worked simultaneously, the discharged water from the lower pump kept the cistern full.