2. Setting up Water Hammer Elimination Devices
(1) Adopting Constant Pressure Control Technology:
A PLC automatic control system is used to control the variable frequency speed regulation of the pumps, enabling automatic control of the entire water supply pump station system. Since the pressure in the water supply network constantly changes with varying operating conditions, low pressure or overpressure phenomena frequently occur during system operation, easily leading to water hammer and causing damage to pipes and equipment. The PLC automatic control system, by detecting and controlling the network pressure, regulates the starting, stopping, and speed of the pumps, controlling the flow rate, and thus maintaining a constant pressure level. The pump supply pressure can be set via the control microcomputer to maintain constant pressure water supply, avoiding excessive pressure fluctuations and reducing the probability of water hammer.
(2) Installing Water Hammer Eliminators
This device mainly prevents water hammer caused by pump shutdown. It is generally installed near the pump outlet pipe and uses the pipe's own pressure as power for automatic low-pressure operation. That is, when the pressure in the pipe is lower than the set protection value, the drain outlet automatically opens to release water and relieve pressure, balancing the pressure in the local pipeline and preventing water hammer from impacting equipment and pipes. Eliminators are generally divided into mechanical and hydraulic types. Mechanical eliminators require manual reset after activation, while hydraulic eliminators can reset automatically.
(3) Installing Slow-Closing Check Valves on Large-Diameter Pump Outlet Pipes
This can effectively eliminate water hammer caused by pump shutdown, but because a certain amount of water flows back when the valve operates, the suction well must have an overflow pipe. Slow-closing check valves come in two types: weighted and accumulator types. The valve closing time can be adjusted within a certain range as needed. Generally, the valve closes 70% to 80% within 3 to 7 seconds after a power outage, and the remaining 20% to 30% of the closing time is adjusted according to the pump and pipeline conditions, generally in the range of 10 to 30 seconds. It is worth noting that when there is a hump in the pipeline and separation water hammer occurs, the effect of the slow-closing check valve is very limited.
(4) Setting up a Unidirectional Pressure Regulating Tower
Built near the pump station or at an appropriate location in the pipeline, the height of the unidirectional pressure regulating tower is lower than the pipeline pressure at that point. When the pressure in the pipeline is lower than the water level in the tower, the regulating tower supplies water to the pipeline, preventing water column separation and avoiding separation water hammer. However, its pressure reduction effect is limited for water hammer other than pump-stop water hammer, such as valve-closing water hammer. In addition, the one-way valve used in the one-way pressure regulating tower must be absolutely reliable; if the valve fails, it may lead to significant water hammer.
(5) Installing a bypass pipe (valve) in the pumping station
During normal operation of the pumping system, the water pressure on the discharge side of the pump is higher than that on the suction side, and the check valve is closed. When a power failure suddenly stops the pump, the pressure at the pump station outlet drops sharply, while the pressure on the suction side rises sharply. Under this pressure difference, the transient high-pressure water in the suction manifold pushes open the check valve plate and flows to the transient low-pressure water in the discharge manifold, increasing the low water pressure there; on the other hand, it also reduces the water hammer pressure rise on the suction side of the pump. In this way, the water hammer pressure rise and fall on both sides of the pumping station are controlled, effectively reducing and preventing water hammer damage.
(6) Installing multi-stage check valves
In longer water pipelines, one or more check valves are added to divide the pipeline into several sections, each with a check valve. When water flows backward in the pipeline during the water hammer process, the check valves close successively, dividing the backflow into several sections. Because the static head in each section of the pipeline (or backflow section) is relatively small, the water hammer pressure rise is reduced. This protective measure can be effectively used in situations with large geometric water supply head differences; however, it cannot eliminate the possibility of water column separation. Its biggest disadvantage is that it increases pump power consumption and water supply costs during normal operation.