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What Is Pump Priming? | Process Engineering Glossary
What Is Pump Priming?
Pump priming is the process of filling a centrifugal pump’s casing and suction piping with liquid before startup, removing any trapped air or vapor that would otherwise prevent the pump from developing suction and delivering flow. Centrifugal pumps rely on liquid, not air, to develop the suction lift needed to draw fluid in, meaning an unprimed pump running with air in the casing will simply fail to pump despite the impeller turning at full speed.
Priming methods vary depending on pump installation, ranging from simple gravity filling for pumps installed below the liquid source, to foot valves that retain liquid in the suction line between runs, to dedicated priming systems for pumps installed in a suction lift configuration above their source.
Applications of Pump Priming
Pump Startup Procedures
Standard operating procedures for centrifugal pumps typically include a priming verification step before startup, particularly for pumps installed in configurations prone to losing prime between runs.
Suction Lift Pump Installations
Pumps installed above their liquid source, in a suction lift configuration, require specific priming provisions since they can’t rely on gravity alone to keep the casing filled with liquid.
Self-Priming Pump Design
Self-priming centrifugal pumps incorporate design features that allow them to evacuate trapped air from the suction line automatically, reducing reliance on manual priming procedures.
Benefits of Knowing Pump Priming
Prevents dry running damage at startup. Proper priming procedures prevent a pump from running dry during startup, avoiding the seal and bearing damage that dry running can quickly cause.
Supports reliable pump startup across different installations. Understanding appropriate priming methods for a given pump configuration supports consistent, reliable startup regardless of installation type.
Informs appropriate pump and accessory selection. Recognizing priming challenges for a given installation supports selecting appropriate accessories, such as foot valves or self-priming pump designs, from the outset.
Limitations to Consider
Suction lift configurations add ongoing priming risk. Pumps in a suction lift arrangement remain vulnerable to losing prime between runs if foot valves or other retention measures fail.
Self-priming designs have capacity and lift limitations. Self-priming pumps can typically only handle a limited suction lift and air volume, making them unsuitable for every application.
Manual priming procedures depend on operator diligence. Where manual priming is required, consistent operator adherence to proper procedures is essential to avoiding dry running incidents.
Pump Priming FAQ
How does pump priming relate to dry running prevention?
Proper priming directly prevents the dry running condition that can quickly damage a pump’s seals and bearings during startup, a concern also relevant to the Venturi effect principle some jet-assisted priming systems rely on.
Why is pump priming particularly important after vapor lock?
A pump that has lost its prime due to vapor lock typically requires the same re-priming procedures used for initial startup before normal operation can resume.
How does pump priming relate to low-low level trip protection?
A low-low level trip helps prevent a pump from running dry due to insufficient suction level in the first place, complementing proper priming procedures as part of overall pump protection, alongside pump curve data, deadheading prevention, appropriate can pump selection, and correct line sizing of the suction line.
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