d. During normal operation, the pump discharge pressure is 150 5 psi
when pump suction pressure is above 20 psi.
When pump suction pressure
falls to 20 psi or less, the speed control governor reduces engine speed.
At a suction pressure of 10 psi or less, engine speed is reduced to idle
(1,000 RPM) to prevent possible collapse of the suction line and/or damage
to the unit.
Similarly, if pump suction pressure rises above 120 psi,
engine speed reduces to idle to prevent pump discharge pressure from
exceeding 155 psi.
This prevents possible hose line damage due to
excessively high pressure.
3. The TWDS is designed so that the lead pumping station can be operated in
the manual or electric manual mode while the down-line boost pumping
stations can be operated in the manual, electric manual, or automatic mode
after the initial start-up.
a. The lead pumping station must be permanently manned during TWDS
operations, while the boost pumping stations operating in the electric
automatic mode require only periodic monitoring and refueling.
At a
minimum, a crew must service each of the boost pumping stations every three
hours while the TWDS is operating.
If one of the boost pumping stations
fails while unattended, the TWDS continues to operate at reduced capacity.
b. When any pumping station is operated in the manual or electric
manual mode, it must be monitored for low suction pressure or high discharge
pressure.
Low suction pressure can result from improper spacing of the
pumping stations; an obstruction, pinch-point, or break in the up-line hose
line; a closed up-line valve; or a disabled up-line pump.
c. Filling a storage bag/tank may also cause a temporary loss in
suction pressure to a down-line pumping station.
High discharge pressure
can result from high suction pressure, a closed down-line valve, or a pinch-
point or obstruction in the down-line hose line.
If a pumping station
suction pressure falls below 10 psi or if discharge pressure rises above 155
psi, engine speed must be manually reduced to idle until the reason for the
improper condition has been identified and corrected.
d. The pump at the lead pumping station must be primed before starting.
The pumps at the down-line boost pumping stations are started upon arrival
of the water column from the lead or up-line pumping station. It takes the
advancing water column approximately 20 minutes to travel 2 miles.
If a
boost pumping station pump does not start when the water column arrives, the
butterfly valve at the suction port on the pump must be closed to prevent
the arriving water column from rushing through the pump and creating a
turbine effect which
3-3
QM4912
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