PROJ00032

• Contract/PO #: C153465
• Contractor Name: City of Cortez and Dolores Water Conservancy District
• Contract Type: Loan
• Water District: 71
• County: Dolores
• Bill Number: HB 83-1102
• Loan Projects - Doc Type: Feasibility Study

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4-3

Blowoff Connections. Outlets for draining the pipeline should be
provided at low points in the system. The exact location of blowoff
outlets is influenced by opportunities to dispose of water. Exact
location of drain or blowoff connections will be determined during
detailed design as the vertical profile of the pipeline is firmly
established. The cost of these fittings will be minimal, but will
improve the maintainability of the line. A typical detail of a
blowoff station is shown on Figure 4-2.

Air valves. Air valves are installed in pipelines to admit or
vent air. There are basically two types: air-release valves and
air-and-vacuum valves. In addition, a combination air valve is
available that combines the functions of an air-release valve and an
air-and-vacuum valve.

Air-release valves
pressure at high points
steep for the air to
accumulation of air can
capacity.

are used to release air entrained under
of a pipeline where the pipe slopes are too
be carried through with the flow. The
become so large as to impair the pipe's flow

Air-release valves are installed at the high points to provide
for the continuous venting of accumulated air. An air-release valve
consists of a chamber in which a float operates through levers to
open a small air vent in the chamber top as air accumulates and to
close the vent as the water level rises. The float must operate
against an air pressure equal to the water pressure and must be able
to sustain the maximum pipeline pressure. A typical detail of a air-
release valve is shown on Figure 4-3.

Air-and-vacuum valves are used to admit air into a pipe to
prevent the cre'ation of a vacuum that may be the result of a-- valve
operation, the rapid draining or failure of a pipe, a column
separation, or other causes. A large vacuum could cause the pipe to
collapse from atmospheric pressure.

Air-and-vacuum valves also serve to vent air from the pipeline
while it is filling with water. An air-and-vacuum valve consists of
a chamber with a float that is generally center guided. The float
opens and closes against a large air vent. As the water level
recedes in the chamber, air is permitted to enter; as the water level
rises, air is vented. The air-and-vacuum valve does not vent air
under pressure.

Air-release valves and air-and-vacuum valves, must be located
above or immediately adjacent to the pipeline. The connecting pipe
should rise gradually to the air valve to permit flow of the air to
the valve for venting. The performance requirements of the valves
are based on the venting capacity (cubic feet of free air per second)

BROWN AND CALDWELL C CONSULTING ENGINEERS