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

will typically be at the margins of the street intersection that contains a grid junction
and also intermediate line valves at street margin of the desired location.
E. Clearances
Clearances around a valve are very important to operations and maintenance of the
valve. When placing a valve in a vault, the design engineer should ensure that
maintenance staff will have access to all valve parts for maintenance and enough space
for wrenches and other tools. Typically, a minimum of 1-foot space is needed around all
valves. SPU prefers a 3-foot space.
F. Valve Restraint Systems
All valves in chambers and those installed on a restrained joint pipe should be fully
restrained. There are several options for restraining valves, including flanges and a
mechanical joint with a wedge restraint gland. The system chosen should be consistent
with other SPU designs and consistent across the project.
G. Valve Replacement
The design engineer should pay close attention to removal of the valve. Valves 16-inch
and larger should have an access hatch directly over the valve, adequately sized to
remove the valve.
Another consideration for valve removal is a dismantling joint. When flanged valves are
installed, the pipeline is extremely tight. If the valve needs to be replaced, unbolting it
may not provide sufficient space to slide the valve out. A dismantling joint has a special
sleeve that can be retracted a few inches. This allows enough extra space to remove the
valve. The dismantling joint also provides some adjustment if a different brand or style
of valve is installed in the future. SPU standard practice is to install a dismantling joint
on valves 16-inch and larger in diameter.
5.6.4.2 Access Ports
SPU installs access ports only on large-diameter (24” or greater) pipelines.
Access ports provide access during construction and to Field Operations and Maintenance staff.
Typical access port sizes are 24-inches in diameter. Typical spacing for a large transmission main
is 1,200 feet except in low areas subject to high groundwater tables. Because access ports
typically only extend 1 to 2 feet above the pipeline surface, they can be buried or encased in a
maintenance hole that extends to the surface. If the access port is fully buried, it should be well
documented on the record drawing (as-built) so future O&M staff can find it. If possible, a
waterline marker should be installed over the access port.
SPU typically installs all access ports vertically. In certain cases, a side-mounted access port may
be necessary given space restrictions. See the DSG standard access port details (Appendix A).
5.6.4.3 Air Gap Structures
Air gaps, also known as goosenecks, are required to prevent cross connections between the
domestic water supply and any other liquid. The ultimate function of this air gap is similar to
that of a check valve. Typically, air gap structures are located on facilities (e.g. tanks) or
equipment (e.g. pumps) connected to the system. The gooseneck discharge must be a minimum
of two discharge pipe diameters aboveground or receiving water surface. Floodwater surface
5-34 SPU Design Standards and Guidelines