Check valves are essential components in piping systems designed to prevent backflow of fluids. These valves operate using the kinetic energy of the flowing medium, automatically opening and closing based on flow direction. In heating systems, check valves are commonly installed at the pump outlet to ensure that fluid does not flow in the reverse direction, which could cause damage or inefficiency. Selecting the appropriate type of check valve is crucial for preventing water hammer effects, a common issue in pumping stations.
Many water hammer incidents are directly related to the check valve located at the pump outlet. When the pump stops suddenly, the fluid may begin to flow backward, creating a reverse flow. Under the influence of this reverse flow, the check valve should close quickly. However, if the valve is affected by mechanical issues, bearing friction, or inertia, it may not close promptly. This delay can result in a significant pressure surge at the check valve location when the reverse flow reaches its peak, potentially causing severe damage to the system.
The check valve flap typically closes when the flow rate drops to zero. It is generally considered normal for the flap to close near this point, though it cannot fully seal when the flow is completely stopped. Properly functioning check valves are essential for maintaining system stability and reducing stress on pipelines.
In hot water heating systems, one effective way to reduce the risk of water hammer caused by pump shutdowns is to install a pressure relief bypass pipe equipped with a check valve. This bypass is usually placed between the discharge side of the circulating pump and the suction side. While the pump is running, the check valve remains closed due to the higher pressure on the discharge side. When the pump stops abruptly, the pressure on the discharge side drops rapidly, while the suction side experiences a sudden increase. This pressure difference causes the fluid from the suction side to push the check valve open, allowing the excess pressure to be released safely. This helps to minimize pressure surges in the system and prevents potential damage from water hammer.
The check valve on the pressure relief bypass must be designed for low resistance and quick response. The larger the diameter of the bypass pipe, the more effectively it can mitigate water hammer effects. The optimal size of the bypass pipe can be determined through transient analysis, taking into account the allowable pressure limits for the system.
When no bypass is installed between the discharge and suction pipes of the pump, the pressure at the pump outlet fluctuates significantly over time. However, adding a bypass with a check valve dramatically improves the situation. The pressure curve stabilizes more quickly, and the amplitude of pressure oscillations is significantly reduced. This design proves highly effective in controlling water hammer and ensuring a smoother, more stable operation of the heating system.
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