Centrifugal Pump Piping Design: Basic rules for centrifugal pump piping

When installing a new centrifugal pump, the pump's piping design is sometimes overlooked. Often, the focus during installation is on the equipment itself, rather than the piping supplying it. However, improper piping during centrifugal pump installation can lead to premature and recurring pump failures during its lifespan. Following these six simple rules can help prevent premature pump component failure and related piping problems.

1. Keep the suction tubing as short as possible.

Leave a straight pipe section of 5 to 10 times the pipe diameter between the pump inlet and any obstructions in the suction line. Note: Obstructions include valves, elbows, tees, etc.

Maintaining a shorter pump suction line ensures the lowest possible inlet pressure drop. A straight pipe section ensures a uniform flow velocity throughout the entire pipe diameter at the pump inlet. Both are important for achieving optimal suction performance.

2. The diameter of the suction-side piping should be ≥ the pump inlet size.

Pipe size is a balance between cost and friction losses. Larger pipe diameters are more expensive, while smaller diameters result in greater friction losses in the system. In terms of diameter, the outlet pipe diameter should generally match the outlet flange on the pump, but it can be slightly larger to reduce friction losses and lower system pressure. On the suction side, the diameter can be the same, but engineers typically choose a size one or two sizes larger, thus requiring an eccentric reducer. If the liquid viscosity is greater than that of water, a larger suction pipe is usually chosen on the suction side. This also helps to create a uniform flow towards the pump and avoid cavitation.

3. Use an eccentric reducer on the suction side

When pipe size conversion is required, consider using an eccentric reducer on the pump suction side. When the fluid comes from below the pump, the reducer will be installed with the top flat. If the fluid comes from above the pump, the reducer will be installed with the bottom flat. This design aims to prevent the formation of air pockets on the pump suction side.

4. Eliminate elbows installed at and near the pump inlet.

Install a straight pipe section of 5 to 10 times the pump diameter between the pump inlet and the elbow. This helps eliminate the "lateral load" on the pump impeller and generates a more uniform axial bearing load on the pump.

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

1. Maintain a sufficient liquid level in the supply tank to prevent eddies and air entrainment.
2. Avoid creating high cavities in the suction line that could trap air.
3. Under suction vacuum conditions, maintain the seals of all pipe and joint connections to prevent air from entering the pump.

6. Ensure piping layout does not put pressure on the pump housing.

The pump must not be used as a support for the suction or discharge piping. Any stress the piping system places on the pump housing will significantly reduce the pump's lifespan and performance.

Remember, improving pump performance can compensate for improper piping layout on the pump outlet side. However, problems on the suction side can be the root cause of recurring failures and, if not properly addressed, can lead to years of problems. Suction-side piping issues are the cause of most pump failures.

Pipe design is an area where fundamental principles are often overlooked, resulting in increased vibration, premature seal and bearing failure. Incorrect piping has long been considered one of the causes of these failures, as many other factors can also lead to equipment malfunction. Many experienced engineers might say that a pump with incorrect piping can still operate normally. While this statement has some merit, it does not mean that problematic piping practices are correct.