TM 5-813-9
c. Meter runs. At meter locations the required
control valve is a valve that modulates the flow
straight approach and downstream length of
through it to provide the desired downstream or
straight pipe must be considered. It is good practice
upstream pressure or flow rate. Although almost all
to allow straight runs of 10 and 5 pipe diameters
valves can be partly closed and control flow to
for upstream (approach) and downstream of meters
some degree, the term "control valve" means a
in the piping layout. This will accommodate any
specialized type of power-activated valve designed
type of meter.
to modulate flow to meet system demands or for
surge protection. The term "pump" as a final
3-6. Controls.
control element is a pump provided with automatic
variable speed control drive to maintain an essen-
a. Description. Pump controls will have the ca-
tially fixed flow rate and for controlled flow rate
pability to provide the desired flow rates, pressures
increase/decrease a t start/stop of pump to mini-
and liquid levels; to provide protection from pump
mize surges in the system. Because of unique
and piping system damage; and to serve as a tool to
features available from control equipment manu-
find system problems which may need operational
facturers, the designer should contact the manu-
adjustment, repair or maintenance. Control systems
facturers before selecting valve and pump control
consist of the following:
equipment.
(1) Sensing and measuring elements (primary
device).
pumping station will supervise and monitor the
(2) Comparison and relaying element (con-
routine operation of pumps, their drives and acces-
troller).
sories to sustain a desired level of performance and
(3) Final control element (as a valve) to pro-
reliability. Alarm situations will be identified, such
duce the required change including an actuator to
as low delivery flow and low pressure, pump
move the control element.
failure, power failure, and low suction head (water
b. Pump control systems are divided into on-off
loss). Alarm situations will include engine drives as
and modular. The successful operation of the
required to support the system reliability fac-
control system depends on several factors as fol-
tors. The type and extent of supervisory instru-
lows:
mentation for the installation will be determined
(1) An accurate definition of the control job to
from:
be done.
(1) Pump application in terms of what effect the
(2) A review and evaluation of available devi-
pump will have on the system if it failed to perform
ces/systems suited to do this specific job.
its function.
(3) Selection of device and system design in
(2) Pump design, type, size and parameters that
cooperation with the manufacturer of the selected
could affect reliability and hydraulic performance
equipment.
such as variable speed pumps and long shaft high
c. Sensing and measuring elements. Automatic
speed pumps, which may need monitoring of
pump control and valve operation sensing and
vibration, bearing and hydraulic performance.
measuring elements will detect values of changes in
(3) Operator experience with similar pumps
liquid level pressure or flow rate and emit a signal
may indicate a need for applying supervisory
which may be amplified and/or converted into
another medium in a transducer as rotary motion or
(4) Installations with operators in attendance
air pressure to electric voltage. The most common
will need minimum monitoring while unattended
primary devices used in waterworks are liquid level
pump stations in remote location will require
sensors, pressure sensors and flow meters.
substantial monitoring of measurements and alarms.
able that is most convenient or advantageous to
3-7. Reliability Factors.
measure is rarely the one best suited for direct use
a. General. A pumping station usually repre-
in the control system or for actuation of the final
control element. Conversion of sensed or measured
sents one of the major and most costly components
variable values into another signal medium is
of a water distribution system, therefore pump
therefore necessary. The comparison and relaying
station reliability will be considered. The number of
means, the transducers and transmitters, are usually
pumps will depend upon present and future needs.
housed together in the controller which often is
An economic analysis should be performed to
physically separated from the primary device.
determine the number of pumps to be installed. In
e. Final control element. For the final control
smaller stations a single pump may be most
element, valves and pumps serve for on-off control
economical to meet the peak demand. Whenever a
and modulating needs in water pumping systems. A
single pump is sufficient, two equal size pumps,
3-7
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