氣缸旋塞
氣缸是蒸汽機車上，用於容納推動車輪的活塞。氣缸通常位於車輛前端，左右各一。蒸氣自汽室供應，並以逆轉機調節每個活塞循環注入汽缸的蒸氣量。
汽缸內的蒸氣推動當中透過連桿與車輪相連的活塞，進一步推動車輛。使用過的蒸汽會由「煙箱」內的「廢汽噴口」排出，在當中與來自火箱的煙霧混合，最後透過煙囪排放至大氣中。
因氣缸與鍋爐和火箱有段距離，當高溫蒸氣不再持續注入汽缸，如車輛靜止或滑行時，殘存蒸氣將因氣缸溫度迅速降低，自然凝結成水。若汽缸中聚積一定水量，每活塞循環將發出水聲。這非常危險，因水不像蒸汽能被活塞壓縮，將導致氣缸破裂並，使動力總成失效。
To prevent this, steam engines come equipped with cylinder cocks. They are usually operated by a lever from inside the cab, and allow water to be expelled from the cylinders. However, since steam escapes through the cocks too, they should only remain open for a short time, typically just a few seconds, when the vehicle begins moving from a standstill.