In localities where the water supply carries large quantities of clay or loam in suspension, a boiler with a mud drum or sediment chamber, Fig.

131, should be used. The boiler will then serve as a settling basin and most of the suspended matter will settle to the bottom of the boiler and into the sediment space. It can then be washed out at suitable intervals by opening the blow-off cock at the bottom of the boiler. If the particles held in suspension in the water are comparatively coarse, about fifty per cent, will be removed by sedimentation.

Hot Water Tanks are large wrought-iron or steel storage tanks of 200 gallons or more capacity, used in connection with water heaters. They are generally used plain or painted, but are seldom galvanized, owing to the great cost of galvanizing large tanks. Large hot water tanks are seldom carried in stock, but are made to order. A sketch, showing the location and size of all outlets should accompany all orders for hot water tanks. The size of the tank and pressure of the water should always be considered when ordering, and when storage tanks are extremely large and subject to great internal pressure, stay bolts and cross braces should be used to give the tank additional strength. Boilers and tanks, of whatever type or make, should be tested and guaranteed to stand a pressure of at least double the static pressure of the water to be stored. This is to provide a factor of safety for occasions when the internal pressure is increased by the expansion of the water when heated, or the increased pressure, perhaps double the static pressure, due to water hammer.