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Dead end
25
Dead end
25*1 Description Many pipeline installations involve pipe branches which serve certain functions of supply, but for various reasons may be isolated. Again it might be expedient for the valve producing the isolation to be at the termination point, or extreme end. This leads to a 'dead end' where water hammer may be reflected, adversely, into the main system when events in the main system reach the branch. There may be many configurations, here just one example is presented to demonstrate the problem.
25.2 Tlieoretical example Figure 25.1 shows a simple network comprising a main line and a branch, both leading to storages at the same level. A pumping plant supplies the system at the upstream end and the case of instantaneous start is considered. The analyses consider the valve at D open and then closed leaving the dead end branch BD connected.
Preferred isolation 100 m
129 m
129 m
¥4
15
(200 m)
c
nn o
3
(500 m)
Fig. 25.1 Simple branch system
2
(600 m)
B 1
(500 m)
138 Water hammer: practical solutions Table 25.1 is a suminary of the relevant data. Tabic 25.1 Data No,
Length
C
d
Q
/
1 2 3 4 5
500.00 1000.00 100.00 100.00 100.00
1000.00 1000.00 1000.00 1000.00 1000.00
0.4000 0.4000 0.4000 0.3000 0.3000
0.0143 0.0897 0.0897 0.0754 0.0754
0.0200 0.0200 0.0200 0.0200 1 Branch 0.0200 1 pipes
ON 2.0
HSTAT 129.00
Constant Y
JVALVE 0
JPU 3
HPU 50.00
HC 100.00
X Y
0.0 0.0
1600.0 0.0
GD 25.000
NR 1450
ef 0.80
LNS 1
NRV Y
PS 1.0
25.3 Analytical results The two cases of storage D connected and isolated are considered and the water hammer up to 7.5 s after pump start examined. For comparison purposes the water hammer after start is shown at Nodes 1 and 3 for both cases in Figure 25.2. In Table 25.2 is listed the results showing that with the tank isolated water hammer is of the order of (155.77 - 129)/(143.1 - 129) = 1.90, or 90% greater than the fully connected case at node 1.
- , — I — I — I — I — ^ — I — I — I — I — I — I — I — I — I
1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 Seconds x 10 Fig. 25J Time plot for dead end study
Dead end 139 Tible 2SJ Analytical results ^,
Open branch Closed branch
143.1 155.77
Hy
163.9 163.9
These results suggest that it would be better to provide for isolation at B rather than D.
25.4 Typical multi-branching A similar situation, though seemingly not as obvious a problem, is the connection of a long pumping main to a cluster of storages, as shown in Figure 25.3.
Pump
^f Fig. 25J
Storage^ cluster
Delivery to a cluster of storages
If the pipe lengths from the common junction to the individual storages are not the same then there may be resonance problems. If the isolation valves (for maintenance purposes), for each storage, are at the storages then the occasion may arise where operations may lead to a similar unfavourable increase in water hammer as demonstrated in the previous case. Although perhaps small, due to the relative lengths of the various pipe sections, it seems trivial to point out that it is unnecessary to add to the general problem of system water hammer by adopting a practice of isolation in this way. The best procedure would be to isolate the storages as near to the common connection as possible, as shown. This does not necessarily solve all resonance problems which are considered elsewhere.
Dead end
25*1 Description Many pipeline installations involve pipe branches which serve certain functions of supply, but for various reasons may be isolated. Again it might be expedient for the valve producing the isolation to be at the termination point, or extreme end. This leads to a 'dead end' where water hammer may be reflected, adversely, into the main system when events in the main system reach the branch. There may be many configurations, here just one example is presented to demonstrate the problem.
25.2 Tlieoretical example Figure 25.1 shows a simple network comprising a main line and a branch, both leading to storages at the same level. A pumping plant supplies the system at the upstream end and the case of instantaneous start is considered. The analyses consider the valve at D open and then closed leaving the dead end branch BD connected.
Preferred isolation 100 m
129 m
129 m
¥4
15
(200 m)
c
nn o
3
(500 m)
Fig. 25.1 Simple branch system
2
(600 m)
B 1
(500 m)
138 Water hammer: practical solutions Table 25.1 is a suminary of the relevant data. Tabic 25.1 Data No,
Length
C
d
Q
/
1 2 3 4 5
500.00 1000.00 100.00 100.00 100.00
1000.00 1000.00 1000.00 1000.00 1000.00
0.4000 0.4000 0.4000 0.3000 0.3000
0.0143 0.0897 0.0897 0.0754 0.0754
0.0200 0.0200 0.0200 0.0200 1 Branch 0.0200 1 pipes
ON 2.0
HSTAT 129.00
Constant Y
JVALVE 0
JPU 3
HPU 50.00
HC 100.00
X Y
0.0 0.0
1600.0 0.0
GD 25.000
NR 1450
ef 0.80
LNS 1
NRV Y
PS 1.0
25.3 Analytical results The two cases of storage D connected and isolated are considered and the water hammer up to 7.5 s after pump start examined. For comparison purposes the water hammer after start is shown at Nodes 1 and 3 for both cases in Figure 25.2. In Table 25.2 is listed the results showing that with the tank isolated water hammer is of the order of (155.77 - 129)/(143.1 - 129) = 1.90, or 90% greater than the fully connected case at node 1.
- , — I — I — I — I — ^ — I — I — I — I — I — I — I — I — I
1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76 Seconds x 10 Fig. 25J Time plot for dead end study
Dead end 139 Tible 2SJ Analytical results ^,
Open branch Closed branch
143.1 155.77
Hy
163.9 163.9
These results suggest that it would be better to provide for isolation at B rather than D.
25.4 Typical multi-branching A similar situation, though seemingly not as obvious a problem, is the connection of a long pumping main to a cluster of storages, as shown in Figure 25.3.
Pump
^f Fig. 25J
Storage^ cluster
Delivery to a cluster of storages
If the pipe lengths from the common junction to the individual storages are not the same then there may be resonance problems. If the isolation valves (for maintenance purposes), for each storage, are at the storages then the occasion may arise where operations may lead to a similar unfavourable increase in water hammer as demonstrated in the previous case. Although perhaps small, due to the relative lengths of the various pipe sections, it seems trivial to point out that it is unnecessary to add to the general problem of system water hammer by adopting a practice of isolation in this way. The best procedure would be to isolate the storages as near to the common connection as possible, as shown. This does not necessarily solve all resonance problems which are considered elsewhere.