Label the Parts of the Steam Engine

All 20 parts on the diagram

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Moving parts and frame 11

Flywheel Turns with the crankshaft and evens out the engine's speed. It carries the engine past the points where the piston changes direction.
Crankshaft The crank, the eccentric and the flywheel are all fixed on it. It carries the engine's power to the machines it drives.
Crank An arm on the crankshaft. The connecting rod pushes and pulls on the crank pin at its end, and so turns the shaft.
Connecting rod One end swings on the crosshead's pin. The other end goes round with the crank pin.
Crosshead Joins the piston rod to the connecting rod. It slides between the guides, so the piston rod only moves in a straight line.
Crosshead guides They keep the crosshead moving in line with the piston. They are bolted to the bedplate.
Eccentric A round disc fixed on the shaft. Its center is off the shaft's center. As the shaft turns, it moves the eccentric rod to and fro to work the valve.
Eccentric rod It carries the eccentric's to-and-fro movement to the valve rod.
Bedplate The frame that carries the cylinder, the guides and the crankshaft's bearing. It is bolted down to a foundation.
Piston Fits the cylinder and is pushed to and fro by the steam.
Piston rod Joins the piston to the crosshead. It passes out through the cylinder cover.

Steam path 9

Governor The engine spins it. If the engine speeds up, the balls swing outward and the linkage closes the throttle valve a little.
Throttle valve It controls how much steam reaches the engine. The governor works it.
Steam chest Steam from the boiler fills it. Also called the valve chest.
Slide valve Lets steam into one end of the cylinder. At the same time, it lets the used steam out of the other end through the hollow under it.
Valve rod Comes out through the wall of the steam chest. It is worked by the eccentric rod.
Steam ports One leads to each end of the cylinder. The valve opens each in turn to steam, then to the exhaust.
Exhaust port The opening between the two steam ports. The hollow of the slide valve joins it to whichever steam port is exhausting.
Cylinder It is closed by a cover at each end. Steam is let in at one end, then the other, so the piston is pushed both ways.
Stuffing box It is packed round the piston rod. That lets the rod slide through the cylinder cover without steam leaking out.

How this list was compiled: Every name checked on 2026-09-30, a name kept only where two of these use it. (1) H. Haeder and H. H. P. Powles, A Handbook on the Steam Engine (1902, public domain), full text at https://archive.org/details/handbookonsteame00haeduoft : cylinder, piston, piston rod, stuffing box and gland, crosshead and guides bolted to the bed-plate, connecting rod, crank and crank pin, crank shaft, fly-wheel as a speed regulator, eccentric and eccentric rod, slide valve, valve rod or spindle, valve chest or steam chest, steam ports, exhaust port, governor and throttle valve. (2) E. P. Watson, Small Engines and Boilers (1899, public domain), https://archive.org/details/smallenginesboil00watsrich : steam chest, slide valve, valve rod, eccentric and eccentric rod, piston rod, stuffing box, crosshead, guides, connecting rod, crank pin, fly wheel, bed plate. (3) Wikipedia, text only: Steam engine, Stationary steam engine, Slide valve, Crosshead, Eccentric (mechanism), Stuffing box, Centrifugal governor, Valve gear. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; no one engine, nothing traced. Licence: own work

How it works

To label the parts of the steam engine, write a name on the line for each number. Numbers 1 to 11 are on the whole engine, seen from the side. Numbers 12 to 20 are on the cylinder cut open under it.

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Steam engine word bank

In alphabetical order, to copy onto the board: bedplate, connecting rod, crank, crankshaft, crosshead, crosshead guides, cylinder, eccentric, eccentric rod, exhaust port, flywheel, governor, piston, piston rod, slide valve, steam chest, steam ports, stuffing box, throttle valve, valve rod.

Label the parts of the steam engine piston

The lower drawing is the piston's end of the engine, cut open. Nine names belong there: the piston and the cylinder it moves in, the piston rod and the stuffing box it leaves through, and over them the steam chest, the slide valve, its valve rod, the two steam ports and the exhaust port.

Four parts are rods: the piston rod leaves the cylinder, the connecting rod turns the crank, the eccentric and valve rods work the valve.
Numbers 2, 3 and 7 all point to the center of the flywheel: the shaft itself, the arm fixed on it, and the off-center disc.
When marking, also accept valve chest for steam chest, and guide bars or slide bars for the crosshead guides.

Questions and answers

Is a steam engine an external combustion engine?

Yes. The fuel burns outside the engine to raise steam in a boiler, and the steam, kept apart from the fire's gases, does the work. No boiler is on this sheet: the name steam engine can also mean the piston machinery alone.

What is a double-acting steam engine?

One in which steam is applied to both sides of the piston. The engine on this sheet is double-acting: it has a steam port at each end of the cylinder, and a seal where the piston rod comes out.

Why does a steam engine have a crosshead?

To keep sideways force off the piston. The end of the connecting rod swings from side to side as the crank turns, and the crosshead, held between its guides, takes that push. The piston rod only moves in line with the piston.