Patent ID: 7395948

Claim:
A system for sequentially pumping a liquid from multiple storage tanks, the system comprising: a) a rotor pump having: i) a pump housing; ii) at least two inter-engaged rotor elements deployed within said pump housing, each of said rotor elements having a plurality of successively inter-engaging projections, such that a dynamic seal is formed between walls of said pump housing and inter-engaged ones of said projections; iii) at least two spaced apart liquid supply ports configured to supply liquid to at least a first rotor element of said rotor pump, such that a second of said at least two supply ports is reached by said projections of said rotor element after said projections have passed a first of said supply ports; and iv) an outlet for flow of liquid out of said pump housing; b) a first liquid storage tank of variable volume in fluid communication with said first supply port; and c) a second liquid storage tank of variable volume in fluid communication with said second supply port; wherein when said first storage tank is full, liquid is drawn primarily from said first storage tank and as the liquid of said first storage tank is depleted so as to no longer supply the liquid to said first supply port, liquid is drawn primarily from said second storage tank.