Manufacture Hydraulic Pump?

[Vanisle]

I was wondering if anyone has made an actual working hydraulic pump. I think IHBuilder (forgive me if I butcherd your username, going from memory) said he has one in the works.

I planned to try making one with two external teeth gears that mesh inside the pump housing. Like this:

http://en.wikipedia.org/wiki/File:Gear_pump.png

Is it really that easy, assuming you can get the tolerances right?

Obvoiusly one with internal teeth would be harder to do (I just can't come up with an easy way to do internal teeth):

http://en.wikipedia.org/wiki/File:Gear_pump_3.png

A rotary vane pump looks too hard to me. Anybody care to share their ideas or successes?

Richard