A compact, high capacity pump for pumping fluid. A first one-way valve is between an inlet port and the pump's fluid chamber. A second one-way valve is between the pump's fluid chamber and an outlet port. A diaphragm separates a piezoelectric stack from the fluid chamber. A power source provides power to the piezoelectric stack causing it to expand and contract. The expansion and contraction of the piezoelectric stack causes fluid to be pumped from the inlet port to the fluid chamber through the first one-way valve and causes fluid to be pumped from the fluid chamber to the outlet port through the second one-way valve. In one preferred embodiment, both one-way valves are disc valves. In another preferred embodiment both one-way valves are MEMS valves.