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

ange of available sizes, steel pipe size may need to be reduced in the
immediate vicinity of the ball joints. See Virtual Vault plan set 785-38 for an
example of an 89-inch OD steel pipe crossing a slide plane with a 48-inch double
ball expansion joint.
Where fault crossings/slide planes are encountered, a double ball expansion joint should be
installed right at the fault crossing as shown in Virtual Vault plan set 785-38. If this is not
possible, the thickest pipe wall and strongest steel should be used, with some flexibility built in
elsewhere if possible.
Design considerations such as predicted ground movement, installation cost, cost of failure, and
reliability must be analyzed. It may be cheaper to install an inexpensive pipe system and replace
it every 10 years than to install a system that will last 100 years. Some SPU pipelines are
extremely critical and must be designed to withstand the largest expected ground movement.
5.8.4.3 Seismically Actuated Valves
Seismically actuated valves automatically close during an earthquake to prevent the
uncontrolled drainage from water storage tanks due to broken downstream pipelines. Many
factors must be determined for each valve installation: sensitivity, speed to close, battery life
requirements, power availability, and SCADA.
The seismic actuator must be properly matched to the valve it protects.
All valves must have a manual operator for emergency operation.
5.8.5 Inter-Connection of Parallel Mains
In some cases, pipelines may be installed parallel, or a new line may be installed near an existing
main. The design engineer should consider whether a connection between the two pipelines is
possible and beneficial. A primary reason to consider the interconnection is draining of the
pipelines. Typically, when a pipeline is drained, millions of gallons of water are wasted. Pumping
from pipeline to pipeline allows for much faster draining than can normally be achieved by
draining to the water system. If parallel or nearby pipelines are interconnected, water from the
pipeline to be drained can be pumped into the other pipeline, thus not wasting water.
The interconnection between mains will likely require room for a pump. If possible, route an
interconnection line from each pipeline into a single vault, leaving a gap for a pump and the final
connecting piping. The size of the interconnection should be based on flow calculations and an
acceptable amount of time to drain the line. A good location for an intertie is at the blow-off.
5.8.6 Rehabilitation of Existing Mains
See DSG section 5.6.5.
5.8.7 Emergency Pump Connections
See DSG section 5.6.6.
5.8.8 SCADA
See DSG section 5.6.7.
5-46 SPU Design Standards and Guidelines