Proclainer

Just look at it!

(The key element is not merely a pipe; it is a hydraulic cylinder.)

From Wikipedia:

If you where to take two syringes of equal volume and connect them with the tubing, with one syringe filled with water, the other empty and the "piston" completely pushed in, you would see that applying pressure to the full syringe, the empty syringe piston would move out and the distance it is moved out would be equal to the distance the full syringe is moved in.

If you could position the empty syringe vertically and put a weight on the piston you would see that it takes an amount of pressure on the full syringe piston equal to the weight on the empty piston (plus a small amount to overcome friction) to lift the weight.

To explore further, you can try syringes of different volumes, just keep in mind that fluids do not compress like gasses.

On the Proclainer (backhoe) the work done by your thumb on the syringe plunger, is done by the engine and a pump.