SECTION 9: MULTIBURNER HEATER INSTALLATION
9.6.2T and Fork Layouts and Manifold Tube Length Rules
See Page 33, Figure 21 through Page 34, Figure 22 for diagrams of T and Fork layouts. The T and Fork layouts have a tee or cross (called the "last tee" or "last cross") where the combustion gases in the system enter the tee or cross with directly opposing flow directions, which creates an added source of pressure drop in the system. This additional source of pressure drop requires some difference in how the allowed manifold length is calculated. In this case, we have to differentiate manifold tube that is located between the radiant pipe and the last tee (or cross) from manifold tube that is located between the last tee (or cross) and the pump.
First determine the length of manifold tube between the radiant tube end and the last tee (or cross). Do not count any tube length twice. Now refer to Page 30, Table 10 and find the maximum manifold tube length for each burner. Add together the maximum
FIGURE 21: T Layout
manifold tube length on the table for each burner in the system, this is the maximum manifold tube length for the entire system.
To determine the maximum manifold tube allowed between the last tee (or cross) and the pump: Subtract the manifold tube length between the radiant tube and the last tee (or cross) from the maximum manifold length for the entire system, then divide that number by 1.5.
Example: Consider a T layout with two
([45' +
One pair of burners.
Last Tee | Burner |
Manifold tube between joining tee and pump.
Pump
33