Basic rules for pump suction piping or pipework to avoid unnecessary failures in the pumps are the followings:

1. Suction Piping To Be Kept As Short as Possible
Straight run pipe length equal to 5 to 10 times the pipe diameter between the pump inlet and any obstruction in the suction line.
By keeping the pump suction line short ensures that the inlet pressure drop is as low as possible. Straight pipes give you a uniform velocity across the diameter of the pipe at the pump inlet. Both are important for optimization of the pump suction.

2. Pump Cavitation – Pipe Diameter on Suction Side Should be Equal or One Size Larger than Pump Inlet
Pipe sizing is a balancing act between cost and frictional losses. Larger pipes cost more, while smaller pipes introduce more frictional losses into the system. In terms of diameter, the discharge pipe diameter should normally match the discharge flange on the pump, but can be larger to reduce friction losses and reduce system pressure. On the suction side, the diameters can be the same size, but engineers usually choose a larger size or two, thus requiring an eccentric reducer. If the liquid is more viscous than water, a larger suction pipe on the suction side is usually preferred. This also helps to create an even flow to the pump and avoid cavitation.

3. Applying Eccentric Reducers on the Suction Side
When pipe size reduction is required, consider using an eccentric reducer on the suction side of the pump. Install the flats of the reducer on top as the fluid comes out from under the pump. If the fluid comes from the top, the flat part of the reducer should be installed at the bottom of the pipe. The flat portion is designed to prevent air pockets from forming at the pump suction.

4. All the Mounted Elbows Close to the Pump Suction Must be Avoided or Eliminated
To include 5 to 10 diameter straight pipes between the pump suction and the elbow. This helps eliminate “side loading” of the pump impeller and creates an even pump axial bearing load.

5. Elimination of the Possible Air Entrapment in the Pump Suction Line
– Maintain adequate levels in supply tanks to eliminate vortices from forming and air entrapment.
– Avoid high pockets in suction piping, which can trap air.
– Keep all pipe and fitting connections tight in suction vacuum conditions to prevent air from getting into the pump.

6. To Ensure the Arrangement of Pipework Will Not Cause Strain on the Pump Casing
The pump should must not support suction or discharge piping. Any stress on the pump casing by the piping system can greatly reduce pump life and performance. Remember that improving the performance of the pump will help compensate for plumbing errors on the discharge side of the pump. However, problems on the suction side can be a source of repetitive failures that, if not handled properly, can cause problems for years to come. Suction side piping problems cause most pump problems. Piping design is an area where fundamental principles are often overlooked, resulting in increased vibration and premature failure of seals and bearings. Incorrect plumbing has long been overlooked as the cause of these failures due to the many other reasons the equipment could fail. Many experienced engineers might argue that a pump with incorrect piping can still function properly. This argument, while valid, does not make the piping practice in question correct.