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Manual Blow-Off Cocks On 6167 and 6213
Manual blow-off cocks are used to remove sludge and other impurities from inside the boiler. They are normally installed at the lowest point of the boiler, which on steam locomotives is around the firebox. They are operated by a lever usually located in the cab or on the exterior of the locomotive.
As feed water is added to a locomotive boiler and changed to steam, the concentration of Total Dissolved Solids (TDS)- measured in Parts Per Million (PPM), in the boiler steadily increases. Eventually the boiler water would foam, unless preventative measures are taken. Water and dirt would be carried along by this sludgy foam, clogging superheater units, valves and causing excessive wear on cylinders and other surfaces. As well, these accumualting solids have the tendancy to settle near the mud-ring in the form of sludge, which if not removed could then settle on the heating surfaces as scale. This scale acts as an insulating barrier that will interfere with the transfer of heat from the metal of the boiler to the water which will increase fuel consuption and can lead to overheating of the boiler metal which may result in tube failures or other pressure vessel metal damage. By removing and replacing dirty water with considerably cleaner feed water, the amount of TDS in the water can be maintanined at a satisfactory level.
Manaul blow-off cocks can also be used to drain or fill the boiler with water, before and after a boiler washout for example. In addition, the locomotive could also be connected- by means of the blow-off cocks, to a live steam system if it was in a roundhouse so equipped (the CPR's John Street Roundhouse in Toronto used such a system). Blow-off cocks also come in handy in emergencies that require the expulsion of a large quantity of water, such as if the locomotive starts to foam.
CNR 6167 is equipped with two blow-off cocks located on the engineer's side of the firebox. They are linked together and are operated by a lever in the cab located within convienent reach of the engineer. The arrangement seen on 6167 was one of the more common arrangements applied by the CNR to its Northern and Mountain type fleet.
CNR 6167's manual blow-off cocks, and the lever used to operate them.
Right Hand Photo Courtesy Grant Kingsland.
Lastly, while the blow-off cocks on many engines exhaust straight out from the side of the engine, creating a hazard to life and property along the right-of-way, some engines had the piping extended underneath the cab or employed some variety of steam separator. An alternate arangement observed on engines such as 6213 and 6400 can be seen below. Compare 6213's valves with 6167 and note the differences between the two, notably the shut-off valve on 6167's blow-off cocks (which came in handy if the cocks ever got stuck open).
Photos Courtesy Grant Kingsland
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