III. PENSTOCKS, OUTLET PIPES, GATES, VALVES, AND AUXILIARY PIPING
3.1 Penstocks and Outlet Pipes
Penstocks and outlet pipes are steel, concrete, or in some cases wood stave water conduits.
Penstocks and outlet pipes may be entirely or partially embedded in concrete, placed under
ground, or carried on suitable supports above ground or in a tunnel. A penstock is conduit that
conveys water from a reservoir, forebay, or other source to a hydraulic turbine in a hydroelectric
powerplant. An outlet pipe is a conduit that conveys water from a reservoir for irrigation, run of
the river, municipal or industrial water supply, or other purposes. Both penstocks and outlet
pipes may have expansion joints, manholes, drain and fill lines, and other accessories which may
require periodic maintenance.
Many of the penstocks and outlet pipes in Reclamation facilities are over 40 years old. Besides
periodic inspections and maintenance, the condition of these conduits should be evaluated as to
their safety. Due to corrosion and other factors, a penstock or outlet pipe may no longer be safe
for water hammer conditions that may occur during a load rejection or closure of an outlet valve.
Guidelines for Evaluating Aging Penstocks published by the American Society of Civil Engineers
provides useful information and engineering techniques for the assessment of all types of
penstocks and should be consulted in setting up an evaluation program.
3.2 Gates and Valves
There are numerous types of gates and valves installed in Reclamation powerplants and
primary purpose is to regulate flow or to act as a secondary shutoff. The following definitions are
taken from the Handbook of Applied Hydraulics, Third Edition:
. A gate is a closure device in which a leaf or closure member is
moved across the fluidway
from an external position to control the flow of
A valve is a closure device in which the closure member remains fixed axially with respect to the
fluidway and is either rotated or moved longitudinally to control the flow of water.
Guard gates or valves
. Guard gates or valves operate fully open or
closed and function as a
secondary device for shutting off the flow of
water in case the primary closure device becomes
inoperable. Guard gates are usually operated under balanced-pressure no-flow conditions,
except for closure in emergencies.
Regulating gates and valves
. Regulating gates and valves operate
under full pressure and flow
conditions to throttle and vary the rate of