determined by location of the water source.
Boost pumping stations are
intended to be spaced at approximately 2-mile intervals, assuming that the
route is reasonably direct and the terrain is level.
a. A substantial rise or fall in elevation along the hose line route
may require adjustment of standard spacing intervals. If the next down-line
pumping station is substantially higher in elevation than the up-line
pumping station, the distance between them must be shortened. If the next
down-line pumping station is substantially lower in elevation than the up-
line pumping station, the distance between them must be lengthened.
b. Adjustments to spacing between pumping stations (due to elevation
change) assure that water pressure is maintained within optimum operational
range. Under normal conditions, the TWDS delivers water to the suction port
of each boost pumping station at a pressure of 20 psig.
When suction
pressure falls below 20 psig, boost pumping stations are designed to begin
reducing speed, when operated in the electric automatic mode. Therefore, if
an up-line pumping station is substantially lower than the next down-line
station, and the elevation difference has not been offset by spacing
adjustment, suction pressure at the down-line pumping station may fall below
20 psig and cause that pump to slow down. This in turn will cause remaining
down-line boost pumping stations to slow down, seriously degrading overall
performance of the TWDS.
c. After locations for pumping stations have been plotted, check the
ground profile for any sharp declines in elevation along the hose line
route. An excessive drop in elevation significantly increases the pressure
of water as it flows downhill. If pressure builds to 225 psi, the hose line
can rupture and equipment failure results.
Therefore, when the ground
profile indicates a sharp elevation drop along the route, a pressure-
reducing valve must be installed in the hose line.
To determine the
location of the pressure-reducing valve, refer to the ground profile and the
procedures outlined in TM 5-4320-303-10.
If elevation continues to drop
excessively beyond the first pressure-reducing valve installation point, a
second pressure-reducing valve must be installed in the hose line.
5. In selecting a site for the storage assemblies, keep in mind that the
storage assemblies may not be required.
This will depend on the TWDS
mission and that the storage assemblies must be installed near the junction
of two 500-foot lengths of hose line. Select areas which will have a low
potential for environmental damage. When selecting a site for installation
of the distribution points, remember that depending on the TWDS
QM4912
3-6
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