FEED-WATER FILTER,
which removes suspended matter which, if it entered the boiler, would form a deposit round the tubes, and while decreasing their efficiency, make them more liable to burning. The most dangerous element caught by the filters is fatty matter—oil which has entered the cylinders and been carried off by the exhaust steam.
The filter is either high pressure, i.e. situated between the pump and the boiler; or low pressure, i.e. between the pump and the reservoir from which it draws its water. The second class must have large areas, so as not to throttle the supply unduly.
Many kinds of filtering media have been tried—fabrics of silk, calico, cocoanut fibre, towelling, sawdust, cork dust, charcoal, coke; but the ideal substance, at once cheap, easily obtainable, durable, and completely effective, yet remains to be found.
A filter should be so constructed that the filtering substance is very accessible for cleansing or renewal.