usually set at the factory, but you may adjust them in
the shop to a desired pressure. You should install this
valve at approximately the same level as the top of the
Forced hot-water circulating systems use the
flow-control valve shown in figure 4-73. It is normally
installed in the distribution main. This valve prevents
gravitational flow of water through the system. The
valve does not offer any serious resistance to the flow
of water when the circulating pump is in operation.
However, when the pump is not operating, the small
gravitational head of water cannot open the valve.
Each week you should check the flow-control valve for
proper operational down-free movement. Examine the
valve for water leaks and repair it when necessary.
Special Flow Fittings
Various types of special tees designed to deflect
main-line water into the radiator branches are used in
one-pipe and two-pipe forced-circulation systems.
These fittings are designed and calibrated to the size of
the radiator and system-operating temperature.
Fittings of this type are required with one-pipe,
forced-flow systems, and they do equally well for
radiators above and below the distribution mains.
MAINTAINING AND TROUBLESHOOTING
HOT-WATER HEATING SYSTEMS
Hot-water heating systems require little
maintenance other than periodic checks to make
certain that all air is out of the system and all radiators
are full of water. The circulating pumps should be oiled
regularly according to the manufacturer's instructions,
and the pressure-relief valves should be checked
Figure 4-73.One type of flow-control valve.
Some of the common discrepancies encountered
when troubleshooting hot-water heating systems are
contained in appendix II, table O.
Operator maintenance on the electrically driven
feed pump consists mostly of cleaning the pump and
motor. However, the pump motor is lubricated
according to the manufacturer's specifications.
Remember that not using enough lubricant can result
in the bearings running dry or seizing on the motor
shaft. But, too much lubricant causes the motor to
become dirty, and it can result in the motor windings
becoming saturated with oil and burning out.
When a water leak develops around the pump
shaft, tighten the packing-gland nuts or repack the
stuffing box as necessary. The strainer, installed
between the pump and the condensate receiver, should
be kept clean to avoid any restriction of the flow of
water to the pump.
The maintenance of feed-water heaters and
economizers normally includes removing solid matter
that accumulates in the unit; stopping steam and water
leaks; and repairing inoperative traps, floats, valves,
pumps, and other such associated equipment.
What is the main reason to install a two-pipe,
open tank, gravity distribution system over a
one-pipe, open-tank, gravity distribution
Q28. The operations of what component of the
one-pipe, closed-tank distribution system results
in higher heat emission from the radiators?
Air vents release trapped air in the system. If the air
is not released, how would this affect the system?
Learning Objective: Recognize different types of
high-temperature hot-water systems, their components,
and understand their application and installation.
High-temperature hot-water (HTHW) systems
operate at high pressure to maintain water temperature
that exceeds the normal boiling temperature of 212°F
(at atmospheric pressure) used in other types of heating
High-temperature hot-water systems consist of
standard and heavy-duty equipment, including boilers
(sometimes referred to as generators), expansion
drums, system circulator pumps, distribution piping,
and heat-consuming equipment.