The function of blow-off cock is to blow down the sediments collected at the bottom of the drum or to empty the boiler or to lower down the water level in the drum. The blow-off cock is fitted at lowest portion of the boiler. The casing is provided with two flanges—one is connected to the boiler and other is connected to the steam pipe. The plug valve has a hole. When it is desired to discharge the water, the plug valve is turned in a manner so that the hole in plug can align with the hole in casing and water can rush out of the boiler. The flow of water can be stopped by turning the plug such that its solid part comes in line with the hole in casting. The constructional details are shown in Figure 4.22.
Figure 4.22 Blow-off Cock
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