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 (c) Supply risers for ordinary one-pipe systems which carry all the water of condensation and in a direction opposite to the flow of steam.

(d) Risers for one-pipe overhead systems which carry all the water of condensation but in the same direction as the flow of steam, the lowest part of riser below last radiator being solely a return pipe.

(e) Supply risers for two-pipe systems which carry no water condensation, except that due to the pipes themselves.

In addition to these the following classification is made for return pipes:

(f) Return mains for two-pipe and overhead systems which are above the water-line of the system.

(g) Horizontal return mains for two and one-pipe systems which are below the water-line.

(h) Return risers for two-pipe systems.

Table II. herewith gives the maximum amount of radiation to be put on each size of pipe for the different classifications:

The table here given represents the conditions which are to be met with in ordinary buildings, and exceptional conditions will have to be met with by the judgment of the engineer conducting the work. It will be noted in general that this table gives less