Isolation valve closure

[HydroJo]

In a gravity network there can be many isolation (buttefly/gate) valves which may need to be closed in emergency/maintenance situation (e.g. burst pipe event) As a surge analysis expert my normal advice is DONT close these valves against the flow - shut the system down first. Of course in a large gravity distribution network this is not possible.
What is standard procedure? If it is to close isolation valves against flow, the surge pressure must be determined. It's no good relying on the test pressure 5 bar/50% margin as in DI pipe the local pressure rise could be 10 bar !
(NB this is really more relevant in the larger trunk mains of the network, in the smaller branches surge pressures will dissipate.)

 

[25362]

To reduce water hammer effects: close valves slowly, use relief valves, use slow-closing check-valves on pump discharge piping, install air chambers, air spill valves, and consider injecting air into the system.