Table 3. Final pump performance
test results.
Table 1. Pump performance test.
Control Outlet pressure Shaft Hydraulic Current Output
Control
Slurry pump
Outlet
setting Sensor Gauge* speed
drive
draw
flow
setting
Outlet
Hyd.
flow
(%)
(kPa) (kPa) (rpm)
(MPa)
(amps) (visual)
(%)
(kPa)
(MPa)
(visual)
100
103
117
1257
23
50
Full
100
108.9
33
Full pipe
95
103
117
--
23
--
Full
95
108.9
33
Full pipe
90
103
117
1269
23
--
Full
90
108.9
33
Full pipe
85
103
117
--
23
--
Full
85
108.9
33
Full pipe
80
103
117
1270
23
50
Full
80
108.9
33
Full pipe
75
103
117
--
23
--
Full
75
108.9
33
Full pipe
70
103
117
1275
23
--
Full
70
108.9
33
Full pipe
65
103
117
--
23
--
Full
65
104.8
31
Full pipe
60
103
117
1280
23
50
Full
60
95.1
27
Near full pipe
55
103
117
--
23
--
Full
55
85.5
23
Near full pipe
50
103
117
1282
23
--
Full
50
75.8
20
Near full pipe
≈7/8 pipe
45
103
117
--
23
--
Full
45
64.1
16
≈3/4
≈3/4 pipe
40
90
103
1116
18
25
40
54.5
12
≈1/2
≈5/8 pipe
35
76
90
--
13
--
35
47.6
10
≈3/8
1/ to 1/ pipe
30
62
76
806
10
--
30
42.7
6.2
3
2
≈1/4
25
37.9
4.8
Trickle
25
55
70
--
6.6
--
≈7
20
41
55
492
3.4
0
15
48
48
--
5
--
0
run to determine if the these results were valid.
10
--
--
135
--
--
0
Slurry pump outlet pressure was monitored to
5
--
--
--
--
--
0
≈5
determine system capability, as this is a good
0
--
--
0
--
0
indicator of output capability. The results of these
* 1.4 MPa gauge
tests are found in Tables 3 and A2.
brated, a series of tests pumping clean water were
Grates
conducted. In these tests, generator current;
Although the dredge system is designed to
pump RPM; pump inlet, outlet, and hydraulic
process vegetation, the presence of boardwalk
pressures; pump throttle setting; and outflow
and other woody debris was problematic for the
volume were monitored. Results are shown in
pump. Chunks of wood became lodged in the eye
Table 1.
of the pump during dredging operations, and the
Using this data as a baseline, an analysis of the
blockage quickly accumulated other debris in a
pump parameter options was conducted (App.
process called "beaver-damming" (Fig. 6). Evi-
A). In these analyses, various impeller diameters
dence of this phenomenon first surfaced during
were examined at specific speeds, using standard
pumping tests, with cyclic surging, the period of
friction factors for the system components. Power
which was related to impeller speed. The surging
requirements for the 356-mm impeller were
was caused by cavitation due to inlet starvation
checked to ensure compatibility with system
and the backflow of water into the pump. When
capability (Table 2). A top speed of around 1500
pump blockage was suspected, the dredge was
rpm was chosen to allow sufficient power to the
pulled from the water and the pump eye exam-
other components on the dredge system.
ined. It was found to be clogged with debris. The
With the final pump configuration determined
instigators in all occurrences were waterlogged
from analytical methods, pumping tests were re-
sections of boardwalk approximately 70 mm
20 mm 150 to 200 mm long. Because the wood
Table 2. Slurry pump power
was of near-neutral buoyancy, it did not drop out
requirements.
in the expansion (boom) box located ahead of the
Impeller
pump. We also found that aluminum objects did
speed Pressure
Flow
Power
not always drop out.
(rpm)
(MPa)
(L/s)
(kW)
Although the boom box was effective in keep-
1280
24.1
1.4
32.9
ing out the heavier steel debris, it was not func-
1280
31.0
1.4
42.3
tioning when confronted with lighter materials. A
1500
24.1
1.6
38.6
coarse screen system was installed in the boom
1800
24.1
1.9
46.3
box, but that quickly plugged, crippling the
1800
31.0
1.9
59.5
5
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