valves. The pitch is generally not less than 1 inch for
every 10 feet. The piping arrangements for a new
system should provide for draining the entire system.
The radiator transfers heat from the hot water in
the pipes of a hot-water heating system into the
surrounding air in a room. A radiator is usually of two
types. Cast-iron radiators are constructed and
assembled in sections, as shown in figure 4-68, view A.
Damaged radiator sections can be replaced without
replacing the entire radiator assembly. Fin-tube
radiators (fig. 4-68, view B) are constructed of steel
pipe and fins, which are welded to the pipe.
Radiators usually rest on the floor. However, they
can be either mounted on a wall or hung from the
ceiling. The location of a radiator depends on the type
of room to be heated and its location with respect to the
location of the boiler. For instance, in a forced-
circulation hot-water distribution system, the radiators
may be on the same level with the boiler.
Convectors are supported on the wall much in the
same way as a pipe. The convectors consist of a
fin-tube radiator mounted in a metal cabinet and
transfer heat much in the same way, although a
damaged section must be welded or the entire
convector must be replaced (fig. 4-68, view C).
Hot-water heating system radiators and high
points in the distribution lines must have some type of
vent that releases air from the system. Air trapped in
the system prevents the circulation of water. For this
purpose, a manually operated key-type air vent, as
shown in figure 4-69, can be used.
Manually operated key-type air vents can be
replaced by automatic air vents. One type of automatic
air vent is shown in figure 4-70. It automatically allows
the air that forms in the system to escape. When air
vents fail, replace them.
Radiators also have shutoff valves, as shown in
figure 4-71, which reduce or stop the flow of hot water
through a radiator. They are installed in the piping next
to the inlet side of the radiator. Occasionally, you must
tighten the packing nut on these valves to prevent the
water from leaking around the valve stem.
Figure 4-68.Radiators: A. Cast iron; B. Fin tube;
Figure 4-69.A manually operated key-type air vent.