Building Design and Construction Handbook - Merritt - Ventech!

14.6 SECTION FOURTEEN
detergents are used instead of soap, this figure may be stretched considerably. But
when some industrial use of water requires it, the allowable level for hardness must
be diminished appreciably.
Since corrosion can be costly, corrosive water must often be treated in the interest
of economics. In some cases, it may be enough to provide threshold treatment
that will coat distribution lines with a light but protective film of scale. But in other
cases—boiler-feed water for high-pressure boilers, for example—it is important to
have no corrosion or scaling. Then, deaeration and pH control may be necessary.
(The real danger here is the failure of boiler-tube surfaces because of overheating
due to scale formation.)
(American Water Works Association, ‘‘Water Quality and Treatment,’’ McGraw-
Hill Publishing Company, New York; G. M. Fair, J. C. Geyer, and D. A. Okun,
‘‘Elements of Water Supply and Wastewater Disposal,’’ John Wiley & Sons, Inc.,
New York.)
14.5 WATER QUANTITY AND PRESSURES
Quantity of water supplied must be adequate for the needs of occupants and processes
to be carried out in the building. The total water demand may be calculated
by adding the maximum flows at all points of use and applying a factor less than
unity to account for the probability that only some of the fixtures will be operated
simultaneously (Art. 14.8).
In addition, the pressure at which water is delivered to a building must lie within
acceptable limits. Otherwise, low pressures may have to be increased by pumps
and high pressures decreased with pressure-reducing valves. Table 14.1 lists minimum
flow rates and pressures generally required at various water outlets. The pressure
in Table 14.1 is the pressure in the supply pipe near the water outlet while the
outlet is wide open and water is flowing.
In delivery of water to the outlets, there is a pressure drop in the distribution
pipes because of friction. Therefore, water supplied at the entrance to the distri-
TABLE 14.1 Required Minimum Flow Rates and Pressures during Flow for Fixtures
Fixture Pressure, psi* Flow, gpm
Basin faucet 8 3
Basin faucet, self-closing 12 2.5
Sink faucet, 3 ⁄8-in 10 4.5
Sink faucet, 1 ⁄2-in 5 4.5
Dishwasher 15–25 †
Bathtub faucet 5 6
Laundry tub cock, 1 ⁄4-in 5 5
Shower 12 3–10
Water closet ball cock 15 3
Water closet flush valve 15–20 15–40
Urinal flush valve 15–20 15
Garden hose, 50 ft, and sill cock 30 5
* Residual pressure in pipe at entrance to fixture. 20 psi minimum required at water conserving type
fixture. Verify minimum pressure reqirements with fixture manufacturer.
† As specified by fixture manufacturer.