Priming (foaming in North America) is a condition in the

boiler A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central ...

of a

steam locomotive A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the loco ...

in which water is carried over into the steam delivery. It may be caused by impurities in the water, which foams up as it boils, or simply too high a water level. It is harmful to the valves and pistons, as

lubrication Lubrication is the process or technique of using a lubricant to reduce friction and wear and tear in a contact between two surfaces. The study of lubrication is a discipline in the field of tribology. Lubrication mechanisms such as fluid-lubric ...

is washed away, and can be dangerous as any water collecting in the

cylinders A cylinder (from ) has traditionally been a three-dimensional solid, one of the most basic of curvilinear geometric shapes. In elementary geometry, it is considered a prism with a circle as its base. A cylinder may also be defined as an in ...

is not compressible and if trapped may fracture the cylinder head or

piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-t ...

Causes

The most frequent cause is running the locomotive with too high a level of water in the boiler and is most apparent when the regulator is opened sharply or steam demand is high. Thus, sensible locomotive management by the operators will help to prevent the occurrence. The phenomenon is particularly evident in areas of impure water, where boiled water creates a foam, or a mist of droplets, filling the space that collects steam at the top of the boiler, to be drawn down the steam collector pipe in the form of slugs of water. If boiler water is condensed and re-used, any oil or grease must be extracted as this form of contamination is particularly likely to give trouble.

Remedy

Early designers fitted curved sheets below the steam collector pipe, but these were not successful as the whole of the steam space could contain foam. In districts where the feed water is unsuitable, blowdown valves ("scum valves"), either continuously working while the regulator is open or operated in conjunction with the boiler feed, are fitted. Valves at water level reduce surface scum; those towards the bottom of the boiler help remove precipitated solids. Other forms of prevention include the chemical treatment of water before it enters the boiler. In the event of priming (and also when steam is admitted through cold piping or into a cold cylinder) the operators need to open the

cylinder cocks Hydrolock (a shorthand notation for hydrostatic lock or hydraulic lock) is an abnormal condition of any device which is designed to compress a gas by mechanically restraining it; most commonly the reciprocating internal combustion engine, the ...

, which are designed to release trapped water. Once occurring, the problem can affect the level indicated in the boiler's gauge glass and for this reason is difficult to put right without reducing the water level to the extent that the

firebox Firebox may refer to: * Firebox (steam engine), the area where the fuel is burned in a steam engine * Firebox (architecture), the part of a fireplace where fuel is combusted *Firebox Records, a Finnish 8101705801record label * Firebox.com, an elect ...

crown becomes dangerously exposed.

References

* * *{{cite book , last = Woodruff , first = Everett B. , title = Steam Plant Operation , publisher = McGraw Hill Professional , date = 2004 , location = New York , pages = 447 , isbn =0-07-141846-6 , display-authors=etal Steam boilers Steam power Steam engines Steam locomotive technologies

Causes

Remedy

See also

References