【Haichuan Chemical Valve Management】Series of Posts -- What are the hazards of not installing a check valve at the pump outlet?

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This post was last edited by HaiChuan LaoYu on 2026-5-3 08:15. Proper management of valves is essential for stable operation. Everyone is welcome to engage in discussions and share insights regarding this series of posts. [HaiChuan Chemical Valve Management] series of posts: https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=5719309 ---------------------------------------------------------------- Disclaimer: The content contained in this article is intended solely for technical exchange and reference purposes only; it does not constitute any form of professional engineering advice, design basis, or operational guidance. -----------------------------------------------------------------------------------Water hammer is a highly destructive fluid impact phenomenon in pipeline systems; it can cause pipeline vibration and increased noise at minimum, while at worst it can lead to pipeline rupture and pump damage. The absence of a check valve at the pump outlet is one of the most common causes of water hammer. In many operating conditions, operators tend to overlook the function of check valves, thinking that they are only used to prevent backflow of the medium, without realizing that one of their functions is to suppress water hammer. Starting from the formation principle of water hammer and the potential hazards under conditions without check valves, this paper explains the underlying reasons by referring to actual operating conditions, thereby providing a reference for the safe operation of piping systems. To understand this issue, it is first necessary to clarify the basic principle behind water hammer: the fluid in the pipeline possesses inertia and compressibility (although the compressibility of liquids is low, it cannot be ignored during transient processes). When the flow state of a fluid changes suddenly (such as when a pump suddenly stops or a valve closes rapidly), the kinetic energy of the fluid is instantly converted into pressure energy, resulting in a transient pressure wave. This pressure wave propagates and reflects within the pipe, thereby causing the water hammer phenomenon. The check valve at the pump outlet is essentially a valve that automatically prevents the backflow of the medium. Its primary function is to quickly shut off the path for backflow in situations such as when the pump stops, thereby preventing the flow disruption caused by backflow – which is a key factor in the formation of water hammer. When the pump is operating normally, the medium flows steadily downstream through the pipes driven by the pump, with the system pressure and flow rate being in a state of relative balance. When a pump suddenly stops (due to power failure, malfunction, or normal shutdown), the driving force disappears instantaneously. However, due to inertia, the downstream medium continues to flow forward, causing the pressure near the pump outlet to drop rapidly and creating a low-pressure zone (or even liquid column separation). At this point, the downstream medium flows back toward the pump outlet under the effect of the pressure difference, resulting in backflow. The backflowing medium collides with the forward flow remaining in the pump impeller and pipes; simultaneously, the kinetic energy of the backflowing medium is rapidly converted into pressure energy, resulting in an instantaneous high-pressure shock wave. Lacking the obstruction of a check valve, this shock wave propagates rapidly along the pipeline, repeatedly reflecting and building up at weak points where the pipeline geometry changes, such as elbows, tees, valves, and pump bodies, thereby intensifying the water hammer effect. Especially in long-distance pipeline systems, high-head or high-flow pump systems, the backflow velocity is faster and the backflow volume is larger, resulting in higher peak pressures due to water hammer and more significant damage. Additionally, in the absence of a check valve, the backflowing medium can cause the pump impeller to rotate in the reverse direction. This not only increases abnormal wear on the mechanical seal and bearings, but may also lead to severe collisions or even fracture between the impeller and the pump casing, thereby exacerbating the damaging effects of water hammer. After installing a suitable check valve, when the pump stops and the flow rate drops to the shut-off setpoint, the check valve quickly closes under the influence of its own weight, spring force, or the backflowing medium. This blocks the path for reverse flow and prevents any sudden changes in flow kinetic energy, thereby fundamentally preventing the occurrence and intensification of water hammer. It should be specifically noted that the selection of check valves must be matched to the operating parameters of the pump system (such as flow rate, head, properties of the fluid, and pressure level). The closing characteristics (rapid closure, two-stage closure, etc.) should also be chosen appropriately, so that the closing speed is in harmony with the rate at which backflow occurs; this is necessary to ensure effective hammer prevention. If the check valve is improperly selected or installed, it may instead trigger a more severe valve-closing water hammer. Therefore, installing a check valve at the pump outlet is not redundant; rather, it is a crucial measure in system design to suppress water hammer and protect the pipes and the pump itself. Ignoring this step can easily lead to safety accidents and cause significant losses.