peristaltic pumps used in the medical industry might work if I understand your need. These are low volume pumps. There is no impeller. They consist typically of three rollers(ball bearings) on a rotor. The supply tube is wrapped around a cassette containing the rotor. The tube is situated between the housing and the rotor. As the rotor turns the tube is compressed forcing the fluid within the tube to advance (flow). If you could locate one of the auction houses or medical supply/surplus stores you could get one relatively cheap. The advantage is that you could adjust the flow to very low to heavy.
John
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