A pump has a flexible liner which is expanded and contracted by application of
positive and negative fluid pressure for receiving and discharging fluent material.
The liner is received in a rigid shell which defines the maximum volume received.
In discharging fluent material, a vacuum is applied to one side of the liner, while
applying pressure to the other side so the liner is collapsed against the rigid
shell. The liner is arranged so as to be the only part of the pump which contacts
the fluent material, and is replaceable to effect rapid and easy cleaning of the
pump. The liner has multiple pump cells which can expand and contract for moving
fluent material through the pump cell. The pump cells can be sized and arranged
so that by selection of particular pump cells which receive the fluent material,
precise volumes can be metered by the pump.
