5.9 General Design Considerations
a. The water system shall have sufficient capacity to maintain 40 psi at the building entrance for one and two family dwellings. For other development, the system shall have sufficient capacity to provide minimum pressure of 35 psi at the building side of the meter during periods of maximum use, and to provide sufficient volumes of water at adequate pressures to satisfy the maximum expected daily consumption plus fire flows.
b. Normal working pressure in the distribution system should be approximately 70 psi with a range of 40 psi to 100 psi.
c. Head loss shall be determined by the Hazen-Williams equation based on the following coefficients.
Pipe Diameter | C Value |
|---|---|
8 Inches and Less | 100 |
10 to 12 Inches | 110 |
Greater than 12 Inches | 120 |
d. Velocities in mains shall normally range from three (3) to six (6) feet per second for average demand to a maximum velocity of ten (10) feet per second for maximum day demand plus fire flow.
e. A 20 psi residual pressure under fire flow conditions shall be maintained at all points in the distribution system. Generally, a maximum velocity of eight (8) feet per second will govern for sizing mains at all other locations of the service level where this criteria does not govern.
f. Private systems shall limit velocities as required by the Oregon Plumbing Specialty Code, Installation Standards.
g. Providing for Future Development.
1) As a condition of water service, all developments will be required to provide public water mains of sufficient size for fire protection to adjacent parcels, as well as connection (to the new system) of existing water lines, hydrants or services crossed or intercepted by or adjacent to the new waterlines, at locations as required by the City Engineer (see PWDS also 1.6.e). This shall include the extension of water mains in easements across the property to adjoining properties and across the street frontage of the property to adjoining properties when the main is located in the street right-of-way. This shall include extension to the far side of streets fronting or adjacent to the development as required to avoid work within or under these streets in the future. This shall include waterlines that are oversized to provide capacity for required fire flows.
2) Water distribution systems should be designed for maximum development of the service area with recognition of possible urban renewal, industrial expansion, etc.