6 basic rules for piping centrifugal pumps

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When installing a new centrifugal pump, after carefully selecting the right size and materials, how can one ensure that the new pump is installed successfully and correctly? It is crucial to properly set the base and align the pump unit. Furthermore, properly laying the pump’s piping is also extremely important. When installing a new centrifugal pump, the piping design of the pump is sometimes overlooked. Generally, the focus during installation is often on the equipment itself, rather than the pipelines that supply it. However, if the piping layout is improper when installing the centrifugal pump, the pump may fail prematurely and experience repeated failures during its service life. Although the maintenance team carries out regular maintenance and repairs on the pumps, this is actually only a temporary solution rather than a permanent fix. Apart from the (limited) information that may be found in the Installation, Operation, and Maintenance Manual (EOMM), there are very few knowledge resources available on this topic. But by following these 6 simple rules, premature failure of pump components and related issues with the pump piping can be avoided. 1. Keep the suction pipeline as short as possible; leave a straight section with a length equal to 5 to 10 times the pipe diameter between the pump’s suction port and any obstructions in the suction pipeline. Note: Obstacles include valves, elbows, tees, etc. Maintaining a shorter pump suction line ensures that the inlet pressure drop remains as low as possible. The straight pipe section allows the flow velocity throughout the entire pipe diameter at the pump inlet to be uniform. Both are important for achieving the best inhalation effect. 2. The diameter of the suction side pipeline should be ≥ the pump inlet size. The pipeline size represents a balance between cost and friction losses. Larger pipe diameters result in higher costs, while smaller pipe diameters cause greater friction losses in the system. In terms of diameter, the diameter of the outlet pipe should generally match that of the outlet flange on the pump, but it can also be larger to reduce friction losses and lower system pressure. On the suction side, the diameters can be the same, but engineers usually choose a size that is one to two sizes larger, which requires an eccentric reducer. If the viscosity of the liquid is greater than that of water, a suction pipeline with a larger diameter on the suction side is usually chosen. This also helps to create a uniform flow of liquid toward the pump, preventing cavitation. 3. Use an eccentric reducer on the suction side: When a change in pipe size is required, considering the use of an eccentric reducer on the pump’s suction side is an option. When the fluid comes from below the pump, the reducer will be installed with its top level. If the fluid comes from above the pump, the reducing fitting is installed with its bottom flat. The purpose of this design is to prevent the formation of air pockets on the suction side of the pump. 4. Eliminate elbows installed at and near the pump inlet; install a straight pipe section with a diameter 5 to 10 times that of the pipe between the pump inlet and the elbow. This helps to eliminate the “lateral load” on the pump impeller and creates a uniform axial bearing load on the pump. 5. Eliminate the possibility of air accumulation in the suction line: 1) Maintain an adequate liquid level in the supply tank to prevent the formation of vortices and air entrainment. 2) Avoid creating high-volume chambers in the suction line that could trap air. 3) Under suction vacuum conditions, maintain the sealing at all pipe connections and joints to prevent air from entering the pump. 6. Ensure that the piping layout does not exert pressure on the pump casing; the pump must not be used as a support for the suction or discharge pipes. Any stress exerted by the piping system on the pump casing will reduce the pump’s service life and performance. Please keep in mind that improving the performance of the pump helps to compensate for improper piping layout on the pump’s outlet side. However, the issue on the inhalation side may be the root cause of recurring failures, and if not properly addressed, it could lead to problems for many years. Inlet side pipeline problems are the cause of most pump failures. Piping design is a field where a fundamental principle is often overlooked, resulting in increased vibration and premature failure of seals and bearings. For a long time, incorrect piping has been considered one of the causes of these failures, as there are many other factors as well that can lead to equipment failures. Many experienced engineers might say that a pump with incorrect piping can still operate properly. Although this argument makes sense, it does not mean that the problematic piping practice is correct.