The size of return pipes is usually a matter of custom and judgment rather than computation. It is a common rule among steam fitters to make the returns one size smaller than the corresponding steam pipes. This is a good rule for the smaller sizes, but gives a larger return than is necessary for the larger sizes of pipe. Table XVI gives different sizes of steam pipes with the corresponding diameters for dry and sealed returns.

Return Pipes 100074

Fig. 66.

The length of run and number of turns in a return pipe should be noted and any unusual conditions provided for. Where the condensation is discharged through a trap into a lower pressure the sizes given may be slightly reduced, especially among the larger sizes, depending upon the difference in pressures.

Radiators are usually tapped for pipe connections as follows, and these sizes may be used for the connections with the mains or risers.

TWO-PIPE CONNECTION.

Square Feet of Radiation.

Steam.

Return.

10 to 30

3/4"

3/4"

30 to 48

1 "

3/4"

48 to 96

1 1/4"

1 "

96 to 150

1 1/2"

1 1/4"

SINGLE PIPE CONNECTION.

10 to 24

1 "

24 to 60

1 1/4"

60 to 80

1 1/2"

80 to 130

2 "