Priming (steam engine)

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Priming (steam engine) is a condition caused by the build-up of water in the cylinders of a steam engine which is carried over from the boiler due to impurities in the water, which foams up as it boils.

[edit] Causation

This phenomenon is especially evident in areas of 'Hard water', where boiled water creates foam that floats, filling the space that collects steam at the top of the boiler, and is therefore drawn down the steam collector pipe in the form of slugs of water. It is then carried through the superheater (where present), into the cylinders, and theoretically, out of the chimney. However, the priming occurs when these slugs of water are allowed to build up within the cylinder, resulting at best in an adverse effect on lubrication and at worst severe damage to pistons, piston rods or cylinder covers, due to the incompressibility of water.

[edit] Remedy

To help prevent the build-up of water carried over from the boiler, cylinder cocks are provided to allow any water within the cylinder to escape after a locomotive has had a long period of running, or has been idle for long periods of time. Other forms of treatment include the chemical treatment of water prior to it entering the boiler, reducing the carbonate content of the water, and in proportion, the volume of foam created. Also, regular boiler wash-outs which clean out the water spaces and sensible engine management by the Driver and Fireman are further remedies to the situation.