Purgeurs de cylindres

Lorsque la vapeur n'est plus admise dans les cylindres, ceux-ci refroidissent rapidement, car ils sont séparés de la chaudière et du foyer. La vapeur dans les cylindres se condense ainsi en eau assez rapidement. Comme celle-ci n'est pas compressible, contrairement à la vapeur, si une quantité suffisante s'accumule dans les cylindres et est poussée par un piston, elle peut briser les fonds de cylindres et provoquer une avarie de la transmission.

For this reason there are cylinder cocks. They are operated by a valve from inside the cab, allowing water to be released from the cylinders. As some of the steam from the cylinder is lost while the cylinder cocks are open, acceleration is reduced. Typically, the drivers open cylinder cocks for a few seconds after being stationary for some time.

Cylinders can also fill with water in a process called priming. This is the case of the boiler having too much water, or running the vehicle with the cutoff set in the opposite direction, causing water to overflow into the cylinders.

See also: Mechanical Powertrain Damage, Water Level, Cutoff