Non-circular gears (super oval flowmeter)

What is the advantage?

Russell218, I believe hydraulic motors use round gears.

The importance in gear shape is that it can carry liquid from one side to the other with rotation (from the sides, not the center) in such a way that any time if the gears are blocked the input is sealed from the output (so for the flow to exist the gears have to rotate).

I like this! Very much. So much better than just pinwheels. This makes flow meters more unique

Oval gears! Cool. 100th rater.

wad a guy music..

That's weird, I'm sure I posted a response to this before....
You're wrong I'm afraid.
The gears turn due to the fluid passing round the outside of them, not through the middle.
Gear flowmeters (and pumps) have been around for ages, and they rely on the close tolerances between the meshing gears for their efficiency.

...and now my original response re-appears!!! Spooky!

youtube videos to music from Magic-Monkey

Wrong, totally wrong!
If you watch closely (0:28-0:31), the gears turn due to the fluid moving around the outside, i.e. it's not passing through between them.
This is how a gear pump works, the pumped liquid is moved through the housing around the outside of the gears and not through the middle (between them).
In fact they work due to the fact that there IS no leakage between the gears.
Google 'gear pump' and have an enlightening read.