views A and B). The water seal prevents gases and
odors from the sewer from coming into the building or
structure containing the floor drain. Drains without a
water seal (fig. 5-34) may be used when the floor
drains are connected in a system that feeds into a storm
A floor drain that is 2 inches is rated at two
drainage fixture units. A floor drain that is 3 inches is
rated at three drainage fixture units. The load of fixture
units for floor drains is added to the sanitary system,
not the vent system. Most code requirements do not
require floor drains to be vented if they are installed
within 25 feet of a vented drainage pipe line.
Clean, hot water is required in many installations
for domestic and industrial use. Since boiler water
cannot be used for this purpose, because of the
chemicals added, it is necessary to heat additional
water. The water may be heated in tanks equipped
with coiled piping through which the boiler water or
steam circulates. Or it may be heated in independent
units that heat by electricity, gas, solar, or oil.
Domestic water heaters are built in various sizes
from 20, to 50-gallon capacities. Industrial type of
water heaters are designed to heat thousands of
gallons of water, depending upon the amount and
Modern water heaters are self-contained and
require very little attention, since they are fully
automatic. These units are cylindrical in shape, and
they have diameters ranging from about 12 to 30, 40,
Figure 5-34.Drain without a water seal.
and 50 inches, depending upon their capacity. The tank
is constructed of galvanized sheet metal, which may be
lined with a composition of glass to resist corrosion of
the tank lining and prevent contamination of the water.
The combustion chamber is in the lower section, which
is vented by a baffled flue that extends through and
ends at the top of the tank. The entire tank is insulated
to prevent the escape of heat. It is also equipped with a
thermostat which can be adjusted to maintain a certain
water temperature. Safety features which make the
hot-water heater automatic are also in the unit.
Both the cold-water inlet and the warm-water
outlet are at the top of the tank. These tappings are
usually marked INLET and OUTLET. However,
if there is a question in your mind as to which is the
inlet and which is the outlet, just remember that the
cold-water inlet pipe extends over halfway into the
tank, but the outlet pipe does not. There is usually a
drain valve at the bottom of the tank.
You must ensure the dip tube is installed on the
cold-water side or inlet to allow the cold water to go to
the bottom of the heater and not cool the water at the
Gas water heaters must be installed with a relief
valve normally located in the top of the shell. The relief
valve is set to open on a temperature or a pressure rise
of an unsafe limit. Relief valves differ from a safety
valve in that a relief valve opens gradually at a set
point. Normally the valve opens at 210 degrees or at
125 psi at a minimum. The pipe that carries the relieved
water or steam from the tank must extend to within 18
inches of the deck to prevent a hazardous condition.
Always remember that water in a closed vessel,
when heated, will expand and cause the pressure to
rise. If, for some reason, a control fails to turn the heat
source off, the pressure will be relieved by the relief
valve. The water that comes out of the outlet of a relief
valve will flash off due to the pressure change, and you
will experience a hot steam discharge along with very
Q1. What term is used to refer to measurements used
to set water supply and sewer drainage piping?
Q2. One fixture unit is equal to how many cubic
meters of water per minute?
Q3. Using table 5-1, how many fixture units will be
used to install two bathtubs, three water closets,
and a slop sink?