6 Basic Rules For Centrifugal Pump Piping

1. Keep the suction line as short as possible
Leave a straight length of 5 to 10 pipe diameters between the pump suction and any obstructions in the suction line. Note: Obstructions include valves, elbows, tees, etc. Keeping the pump suction line short ensures that the inlet pressure drop is as low as possible. Straight pipe allows for uniform flow velocity across the entire pipe diameter at the pump inlet. Both are important for achieving optimal suction results.

2. The pipe diameter on the suction side should be ≥ the pump inlet size
The pipe size is a balance between cost and friction losses. Larger pipe diameters cost more, while smaller pipe diameters cause more friction losses to the system. In terms of diameter, the diameter of the outlet pipe should usually 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 often choose to go one or two sizes larger, so an eccentric reducer is required. If the liquid viscosity is greater than water, a larger suction line on the suction side is usually selected. This also helps to form a uniform flow to the pump and avoid 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 flow is coming from below the pump, the reducer will be installed top-flat. If the flow is coming from above the pump, the reducer will be installed bottom-flat. The purpose of this design is to prevent air pockets from forming on the suction side of the pump.

4. Eliminate elbows installed at and near the pump inlet
Install a straight pipe section of 5 to 10 pipe diameters between the pump inlet and the elbow. This helps eliminate "side loads" on the pump impeller and creates an even pump axial bearing load.

5. Eliminate the possibility of air entrapment in the suction line
1) Maintain sufficient liquid level in the supply tank to prevent vortex formation and air entrainment.

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

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

6. Ensure that the piping arrangement does not stress the pump casing
The pump should never be used as a support for the suction or discharge piping. Any stress caused by the piping system on the pump casing will greatly reduce the life and performance of the pump. Remember that improved pump performance can help compensate for improper piping arrangements on the discharge side of the pump. However, problems on the suction side can be the source of repetitive failures and can cause years of problems if not properly addressed. Suction side piping problems are the cause of most pump failures. Piping design is an area where basic principles are often overlooked, with the result being increased vibration and premature seal and bearing failures. Improper piping has long been considered one of the causes of these failures, as there are many other reasons that can cause equipment to fail. Many experienced engineers may say that a pump with incorrect piping will still operate normally. While this statement makes sense, it does not prove that the problematic piping practices are correct.