pump question ....

[pugs]

Need 2 to create a pressure zone. A one rotating piece pump would be like a vane pump that has vanes that float in and out to seal and make the pressure zone.

Can also look at gerotar style pumps, like the oil pump in alot of engines. It uses a central gear and a ring gear with the centers of rotation slightly offset.

Edit: Above is for positive displacement style pumps. You can also have non- positive displacement pumps such as a centrifugal but they generally loose alot of pump efficiency as soon as you try to create any kind of pressure i.e. the pump slips.