C-P Systems
What Is a Can Pump? | Process Engineering Glossary
What Is a Can Pump?
A can pump, also called a canned motor pump or sealless pump, is a centrifugal pump in which the motor and impeller are enclosed in a single pressure-containing shell, eliminating the external shaft seal that conventional pumps require to prevent process fluid leakage where the rotating shaft passes through the pump casing. The motor rotor operates submerged in process fluid within the pressure boundary, with a thin-walled can or liner separating the rotor from the stator windings, providing complete containment of the pumped fluid without any dynamic sealing element.
Can pumps are selected for services where eliminating shaft seal leakage is critical, including toxic, flammable, expensive, or environmentally sensitive fluids where even minor seal leakage is unacceptable, making them a key element of process safety management strategies for hazardous fluid handling.
Applications
Hazardous Fluid Services
Can pumps handle toxic, carcinogenic, and highly flammable fluids where conventional mechanical seal leakage would create unacceptable personnel exposure, environmental release, or fire hazard.
High-Vapor-Pressure and Cryogenic Services
Fluids with high vapor pressure or cryogenic fluids that would flash across a conventional seal are well-suited to can pumps, since the sealless design eliminates the seal chamber where flashing typically occurs.
Environmentally Sensitive Applications
Applications where zero fugitive emissions are required use can pumps to eliminate the seal leakage contribution to facility emissions that conventional pumps produce even with well-maintained seals.
Benefits
Eliminates shaft seal leakage entirely. The sealless design removes the most common source of pump leakage, providing complete containment that no mechanical seal can match regardless of seal quality and maintenance.
Reduces seal maintenance cost and downtime. Eliminating the mechanical seal eliminates seal-related maintenance, spare parts inventory, and the unplanned downtime that seal failures cause in conventional pumps.
Supports inherently safer design. Can pumps implement the brownfield and new facility designs principle of containment by eliminating a potential release point rather than relying on a sealing device to prevent it.
Limitations
Lower efficiency than conventional pumps. The fluid-filled gap between rotor and stator introduces additional friction losses, and the can liner creates an air gap that reduces motor efficiency compared to a conventional dry motor.
Process fluid serves as motor coolant and bearing lubricant. The motor and bearings depend on adequate process fluid flow for cooling and lubrication, making can pumps vulnerable to damage from low flow, dry running, or fluids with poor lubricity.
Internal component inspection requires disassembly. Monitoring internal wear and bearing condition is more difficult than in conventional pumps, requiring vibration monitoring and operational parameter trending to detect developing problems.
FAQ
How does can pump selection relate to pump curves?
Can pump pump curves show the same head-flow-efficiency relationships as conventional centrifugal pumps, but typically at lower efficiency points that must be accounted for in the hydraulic analysis.
How does can pump selection relate to process hazard analysis?
Process hazard analysis evaluates whether the consequence reduction from eliminating seal leakage justifies can pump selection, particularly for services where seal failure consequences are severe.
How does can pump specification relate to project engineering?
Can pump specifications are developed during detailed engineering with pump datasheets and P&ID instrumentation requirements reflecting the sealless design’s specific monitoring needs.
Reference
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