6 Basic Rules of Pump Piping

Installing a new centrifugal pump? After carefully selecting the right size and materials, make sure the new pump is set up for success with proper installation. Setting the base correctly and aligning the pump is crucial. It’s also extremely important that piping to the pump is done properly.

Pump piping design is sometimes overlooked when setting up new installations. The focus is more on the equipment than the pipes that supply it. However, when installed with inappropriate piping arrangements, pumps can experience premature and repeated failures during the life of the pump. Maintenance teams will regularly repair the pump, effectively treating the symptom instead of the true problem.

Knowledge and resources are extremely limited on this topic, except what you may find in the Installation, Operation, and Maintenance (IOM) manual (which is minimal). But by following these 6 simple rules, you can avoid premature pump failure and related pump piping pitfalls.

1. KEEP SUCTION PIPING AS SHORT AS POSSIBLE

Include a straight run pipe length equal to 5 to 10 times the pipe diameter between the pump inlet and any obstruction in the suction line. Note: Obstructions include valves, elbows, "tees", and etc.

Keeping the pump suction piping short ensures that the inlet pressure drop is as low as possible. The straight run pipe gives you a uniform velocity across the pipe diameter at the pump inlet. Both are important to achieving optimal suction.

2. PIPE DIAMETER ON SUCTION SIDE SHOULD BE EQUAL OR ONE SIZE LARGER THAN PUMP INLET

Pipe sizing is a balancing act between cost and friction loss. Larger pipes cost more, whereas smaller pipes impose greater friction losses on the system. In terms of diameter, discharge pipe diameter should normally match the discharge flange on the pump but can be larger to reduce friction losses and decrease system pressure. On the suction side, the diameter can be the same size, but oftentimes engineers select a size or two bigger, thus requiring an eccentric reducer. Larger suction piping on the suction side is usually preferred if the liquid viscosity is greater than water.  This also helps produce an even flow to the pump and avoid cavitation.

3. USE ECCENTRIC REDUCERS ON THE SUCTION SIDE

Consider using eccentric reducers on the suction side of the pump when a pipe size transition is required. Install the flat side of the reducer on the top when fluid is coming from below the pump. If the fluid comes from the top, the flat portion of the reducer should be mounted on the bottom of the pipe. The flat portion is designed to discourage an air pocket from forming at the pump suction.

4. ELIMINATE ELBOWS MOUNTED ON OR CLOSE TO THE INLET NOZZLE OF THE PUMP

Include 5 to 10 pipe diameters of straight run pipe between the pump inlet and elbow. This helps to eliminate the "side loading" of the pump impeller and creates uniform pump axial bearing loading.

5. ELIMINATE POTENTIAL FOR AIR ENTRAPMENT IN THE SUCTION PIPING

• 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. ENSURE THE PIPING ARRANGEMENT DOES NOT CAUSE STRAIN ON THE PUMP CASING

Pumps should never support the suction or discharge piping. Any stress on the pump casing by the piping system greatly reduces pump life and performance.

Keep in mind that increasing the performance of the pump will help to make up for piping mistakes made on the discharge side of a pump. Problems on the suction side, however, can be the source of repetitive failures, which could cause problems for years to come if not addressed appropriately. Suction side piping problems cause the majority of pump issues.

Piping design is an area where basic principles are frequently ignored, resulting in increased vibration and premature failure of the seals and bearings. Incorrect piping has long been disregarded as a reason for these failures because of the many other reasons this equipment can fail. Many experienced engineers may argue that pumps with incorrect piping still function and operate as they should. This argument, although valid, does not make questionable piping practices correct.

Contact us today with your questions about correctly installing and piping a pump! We gladly provide technical assistance to businesses and municipalities in Wisconsin, Minnesota, Iowa, and upper Michigan.