Principles for designing pipelines for centrifugal pumps

When installing a new centrifugal pump, how can you be sure that the new pump is installed successfully and correctly after carefully selecting the correct size and materials? It is critical to set up the base correctly and to align the pump set. In addition, it is extremely important to lay the correct tubing of the pump.

When installing a new centrifugal pump, the piping design of the pump is sometimes overlooked. Often, the focus during installation tends to be on the equipment, rather than on the lines that supply it. However, if the piping is not properly arranged when a centrifugal pump is installed, the pump can fail prematurely and repeatedly during its service life. Although the maintenance team regularly performs maintenance and repairs on the pumps, this is actually a palliative rather than a cure.

1. Keep the suction line as short as possible

Leave a straight section length equivalent to 5 to 10 times the pipe diameter between the pump suction nozzle and any obstruction in the suction line. Note: Obstacles include valves, elbows, tees, etc.

Keeping the pump suction line short ensures that the inlet pressure drop is as low as possible. The straight section allows for uniform flow rates throughout the entire diameter at the pump inlet. Both are important for optimal inhalation.

2. The diameter of the line on the suction side should be ≥ pump inlet size

Tubing size is the balance between cost and friction loss. Larger pipe diameters cost more, while smaller pipe diameters cause greater friction loss to the system. In terms of diameter, the diameter of the outlet line should generally match the outlet flange on the pump, but it can also be larger to reduce friction losses and reduce system pressure. On the suction side, the diameter can be the same, but engineers will often choose one or two stops larger, so an eccentric reducer is required. If the viscosity of the liquid is greater than that of water, a suction line with a larger suction side is usually chosen. This also helps to create a uniform flow to the pump and avoids cavitation.

3. Use an eccentric reducer on the suction side

When a pipe size conversion is required, consider using an eccentric reducer on the suction side of the pump. When the fluid comes from under the pump, the reducer will be mounted flat. If the fluid comes from above the pump, the reducer is installed flat on the bottom. The purpose of this design is to prevent the formation of air pockets on the suction side of the pump.

4. Eliminate elbows installed in and near the inlet of the pump

Install a straight pipe section between the pump inlet and the elbow with 5 to 10 times the diameter. This helps to eliminate the "side load" of the pump impeller and creates a uniform pump axial bearing load.

5. Eliminate the possibility of air entrapment in the suction line

1) Maintain sufficient liquid level in the liquid supply tank to prevent the formation of vortex and air entrainment.

2) Avoid the formation of high cavities in the suction line that may entrap air

3) Under the condition of suction vacuum, keep the seal of all pipe and joint connections to prevent air from entering the pump.

6. Make sure that the piping arrangement does not put pressure on the pump housing

The pump should not be used as a support for the suction or discharge lines. Any stress on the pump casing caused by the piping system can significantly reduce the life and performance of the pump.

Keep in mind that improving the performance of the pump can help compensate for the poor routing of the tubing on the outlet side of the pump. However, problems on the suction side can be the source of repetitive failures that can lead to problems for years if not properly addressed. Suction side line problems are the cause of most pump failures.

Piping design is an area where fundamental principles are often overlooked, and the result is increased vibration, seals, and premature bearing failures. Incorrect piping has long been considered one of the causes of these failures, as there are many other causes that can cause equipment failures as well. Many experienced engineers may say that a pump with incorrect piping will still work properly. While this is true, it does not mean that the problematic piping practices are correct.