2013 Water System Plan, Volume II - Seattle City Clerk's Office - City ...

Provide positive online indication of overflow.
5.9.5 Mechanical Appurtenances and Equipment
This section describes mechanical appurtenances and equipment for water storage facilities.
5.9.5.1 Location
To the extent practicable, mechanical appurtenances such as valves, pumps, and controls should
be located in clusters. If applicable, they should be located in mechanical rooms or vaults for
ease of maintenance and security.
5.9.5.2 Penetrations to Storage Cells
Penetrations for pipes, hatches, vents, and sensors into storage cells require special design
considerations to preclude the intrusion of contaminants. The following are general
considerations for mechanical appurtenances and equipment that penetrate storage cells:
Materials and coatings of appurtenances should provide for high resistance to
corrosion.
Open ends of vents and overflow lines should be oriented downward and provided
with 24-mesh, corrosion resistant screens.
Wall and roof penetrations are welded on steel tanks and equipped with seep rings
on concrete reservoirs.
Valve stem penetrations must be sealed to prevent entry of contaminants.
Materials used at penetrations must be selected to avoid creating galvanic currents
between dissimilar metals.
5.9.5.3 Vents
Vents should be located at least 2 feet above finished grade or the 100-year flood
elevation, whichever is greater.
Vents must be sized to allow for adequate air intake during rapid drawdown of the
water level such that the maximum pressure drop within the storage cell does not
impose structural stresses. The acceptable maximum pressure drop is a function of
structural materials and configuration of the storage cell. Acceptable maximum
pressure drop must be established by a design engineer or manufacturer.
5.9.5.4 Overflows
The following are SPU standards for overflow pipes:
1. Overflow pipes must be sized to accept flow rates equal or greater to the maximum
inflow rate to the storage cell.
2. Overflow pipes must terminate 1 to 2 feet but a minimum of two pipe diameters
above grade to provide an air gap, and should be easily visible to O&M staff. Provide
a minimum of two pipe diameters gap.
5-56 SPU Design Standards and Guidelines