Hydraulics and pneumatics

Near the end of the list stands il colpo d’ariete, the surge that runs back up a line when a valve shuts too fast, and the two languages name it after two different things. English reaches for a tool and calls it « water hammer »: something struck the pipe. Italian reaches for an animal. L’ariete is the ram, the male sheep, from Latin aries, and the same word names the zodiac sign and, since antiquity, the beam swung on ropes against a gate — the battering ram. So il colpo d’ariete is the blow that beam delivers, arriving once and hard at the far end of the line. English knows the image perfectly well and simply keeps it elsewhere: the ram of a press, the ram of a cylinder, and the « hydraulic ram », the valve-driven pump that lifts water by using this very surge — which Italian calls l’ariete idraulico. The two languages therefore agree about the machine and disagree about the accident. It is worth fixing before reading a fault report, because ariete in a pipework sentence is never livestock.