The mud drum is attached to a boiler with the expectation that it will
catch and hold the larger portion of the sediment precipitated from
the water. The mud drum to be effective should be protected from the
heat of the fire, for so soon as it receives sufficient heat to boil
the water within it can no longer serve the purpose for which it was
intended as all the sediment which may have gathered would be expelled
by the ebullition of the water. When the drum is located under the
boiler it is not in a good position to catch the sediment, as the
boiling water produces sufficient current to carry the sediment to the
top, or keep it violently agitated, so that there is little opportunity
for it to be deposited anywhere so long as the boiler is making steam.
Afterward when the water is quiet the sediment for the most part is
deposited on the tubes and the curve of the shell; the small portion
falling into the neck of the drum serves principally to show the
inefficiency of the device. Located under the boiler as it generally
is, makes it extremely difficult to get at for examination, and as
a consequence of its being enclosed, as it must be, to be of much
importance, it is subject to greater deterioration than would otherwise
be the case, and as the enclosure to be most efficient would enclose
the neck also, the difference of expansion at or near the junction
would soon produce leaking if not worse. When the mud drum is located
outside the boiler walls where it would be most efficient, if properly
connected, it loses its identity and becomes a mechanical boiler
cleaner. In consequence of these drawbacks the mud drum is becoming
antiquated as a boiler appliance, and is now seldom used.