There is other similar weirdos "container" style pumps popping around, but this one seems familiar as the ram style. Or I have the picture wrong ? What do you know ?

Can be sped up if boring: --->

 

Sure looks like the classic hydraulic ram pump to me.

 

Yup, it's an inertia ram water pump.

My uncle had a version of that on his farm to generate pressure to pump water from a spring up to his house at least 50' above the spring.
It had a 4-5" pipe running about 100' to the ram about 5' below the spring intake level.
You could hear a faint "ping" every few seconds in the house every time the flap valve closed in the pump.
Looked something like this:

 

My dad used one for years.
I make flyback power supplies that work on the same principal.

 

I make flyback power supplies that work on the same principal.

With the transformer inductance being the analog of the water's inertia.

Actually it's probably closer to a boast switching-regulator with the output capacitor the analog for the water pressure chamber partially filled with air.