The Prevention Measures of Water Hammers (2)
Installing the slow closing check valve on the outlet pipe of the large diameter pump
The slow closing check valve can effectively eliminate the water hammer caused by a stopped pump. There must be overflow pipes for suction wells, because a certain backflow will happen in the operation of the slow closing check valve. The slow closing check valve can be classified into the heavy hammer type and the storage type two categories. This kind of slow closing check valve can adjust the closing time of the valve in a certain range based on the requirement. Usually, the slow closing check valve can be closed from 70％ to 80％ after the power is off for 3 to 7 seconds, and the remaining 20 to 30 percent of the closing time is adjusted according to the situation of the pump and pipeline. The closing time is usually from 10 to 30 seconds. The effect of the slow closing check valve on the water hammer which occurs in the pipeline is very effective.
Building the one-way surge tower
Build the one-way surge tower near the pump station or on the proper position of the pipeline, and the height of the one-way surge tower should be lower than the highest water pressure line of the location. When pressure in the pipeline is lower than water pressure in the surge tower, the one-way surge tower will supplement water for the pipeline so as to prevent snapping the water column and the water hammer. However, the reducing pressure effect of the one-way surge tower is limited for the water hammer caused by a closed valve except the water hammer caused by a stopped pump. The performance of the one-way valve which is adopted for a one-way surge tower should be absolutely reliable. Otherwise, once the valve fails, large water hammers may happen.
Equipping the pump station with the bypass pipe (valve)
When the pump system is running normally, the check valve is closed. Because water pressure of the pump’s outlet is higher than that of the suction side. When the pump is stopped due to the accidental power cut, pressure of the pump’s outlet drop dramatically and pressure of the suction side rise dramatically. Under this pressure difference, transient high-pressure water of the suction pipe immediately push the valve plate of the check valve and flow into transient low-pressure water of the outlet pipe, resulting in rising of the location’s low water pressure. In addition, the pressure rise of the pump’s suction side will also drop. The pressure rise and pressure reduction of the pump station’s two sides are controlled in this way, which effectively prevent harm of the water hammer.
Equipping the pipeline with the multi-level check valve
Add one or more check valves on the relatively long water supply pipeline. Divide the water supply pipeline into several sections, and equip the check valve on every section. When backflow happens in the water supply pipeline during the water hammer, every check valve is closed successively to divide backflow into several sections. The hydrostatic head of each section or the backfow section is quite small, resulting in reduction of the water hammer’s pressure rise. This kind of prevention measure can be effectively used for geometric water supply with large differences, but the possibility of the water column separation can not be obviated. The biggest shortcoming of equipping the multi-level check valve is that power consumption of the pump and the cost of water supply increase in the normal operation.
Equipping the high part of the pipeline with automatic discharge and air supplement devices to reduce the impact of the water hammer on the pipeline.
Source: China Steel Pipe Manufacturer – Yaang Pipe Industry (www.pipelinedubai.com)