Operation and Maintenance
The following items can be considered when setting operation and maintenance procedures for a pumping system:
- Time delay—Following a power failure or emergency shutdown, pumps should be restarted only after transients have had sufficient time to decay and air has been removed from the piping as much as possible. A transient decay analysis can be simulated and a timer should be used to prevent a premature pump restart of:
- The diesel pump
- The duty pump (if power resumed quickly)
- The standby power grid
Restart time delays required to allow transients to decay are typically short in terms of water supply (tens of seconds). However, transients caused by a power failure may already have come and gone (in a fraction of second) within the same restart period. Should significant air still remain in the water system, a fast restart of the above device may actually worsen hydraulic transients.
- Slow change of pump operation—Flow in the water system will increase or decrease slowly if the following procedures are applied:
- Air venting—The air trapped at local high points must always be released during both normal and emergency pumping operations. During line filling, air at local high points must be vented in the proper order and pump flow must be much smaller than its design capacity to avoid severe hydraulic transients and pipe breaks.
- Suction system hydraulics—The size of the suction well and/or the suction lines should be designed and operated adequately to prevent spilling or dewatering. Whenever the capacity of the pump station increases, the suction system should be modeled and possibly upgraded to ensure that NPSHA is greater than NPSHR, while the upstream reservoir can freely fluctuate between designed high- and low-water levels.
- Slow change of valve operation—Valve opening or closing times must be long enough. Alternatively, two or more stages can be used, with different stroke speeds for each.
- Alarm setup—Alarm systems should be regularly tested and checked. If false alarms occur frequently, conduct an analysis to determine the causes and provide remedial measures. Otherwise, operators may shutdown the alarm system to eliminate annoyances.
- Maintenance—It is essential to regularly inspect and clean the protection devices, particularly those located outside the pump station.
- Staff training—A workshop can be presented to the engineers and operators, who often know their water system better than any expert. Very often, the system needs to be pushed beyond normal operating ranges to achieve the water-supply objectives. Training is particularly critical for existing pumping stations that have been upgraded many times. It is also possible that operators are not aware of transients occurring far from the pump station, where no one may be present to experience them.