Book - School of Science and Technology

Boiler fittings and mountings 277Table 10.1 Feed and expansion pipes, open vents and relief valvesPipe size (mm)Relief valve, min.clear bore (mm)Boiler rating(kW)Feed andexpansion pipeVent pipeSolid fuelfiringOil or gasfiringup to 74 20 25 20 2575 to 224 25 32 20 25225 to 349 32 40 25 32350 to 399 32 40 32 40400 to 449 40 50 32 40450 to 499 40 50 40 50500 to 749 40 50 50 65750 to 900 50 65 65 80Common vent pipeTo expansioncisternSafetycocksFeed andexpansionpipeFlowLocked valvedBoilersReturnFigure 10.14 Open vent arrangement for multi-boiler plantSteam boilersAs far as fittings and mountings for steam boilers are concerned, stringent requirementsfor these are set out in various of the publications of the Health and Safety Executive.Certain of the mountings are required to be duplicated and the following is no more thana list of the principal items:. safety valves. pressure gauge. water level gauges. steam stop valve. auxiliary steam stop valve. feed and check valve. blow-down valve