Sealless Pumps for a Safer and Greener World
Choosing a canned motor pump is a reliability decision, not just a catalog exercise. The U.S. Department of Energy’s Improving Pumping System Performance sourcebook reports that pumping systems use nearly 20% of global electrical energy. That figure is a reminder to check the full duty point, not just motor power. Flow, head, fluid temperature, viscosity, and solids content all matter. One wrong assumption can show up later as excess energy use or an awkward maintenance job.
Canned motor pumps contain the motor and pump within a sealed assembly, so they can help limit leakage in suitable services. But “sealed” does not mean “fit for every fluid.” Review material compatibility, minimum flow, cooling requirements, and the consequences of a trip. API 685 provides a technical framework for sealless centrifugal pumps used in petroleum, petrochemical, and gas industries; verify that its scope fits your application. Heinz P. Bloch, a recognized rotating-equipment reliability authority, offers a useful principle in his reliability writing: equipment selection should reflect actual operating conditions, not optimistic assumptions. This is a paraphrase, not a verbatim quotation.
Small details count. A pump handling hot, low-viscosity liquid may need a different check than one moving a cool, clean fluid. Ask suppliers for performance data at your operating point, startup guidance, and clear limits for temperature and flow. Then compare lifecycle costs, service access, and spare-parts availability. Not every project gets this right. The best choice is the one your team can operate and maintain reliably.
A canned motor pump should be selected around its real duty point, not a maximum figure copied from a process sheet. Record the required flow in m³/h and head in metres at the same operating condition. For example, a system needing 12 m³/h at 28 m head has a different duty from one needing 12 m³/h at 45 m. Small details matter.
Head must account for elevation, pipe friction, valves, and pressure differences between the suction and discharge vessels. Walk the pipe route if possible; a few tight bends or a partly closed valve can change the estimate. Flow also needs context. Is 12 m³/h continuous, or only a short peak? That is not enough. Note the normal, minimum, and maximum demand, then compare them with the pump’s operating range.
Power in kW depends on flow, head, fluid density, and pump efficiency. A heavier or more viscous liquid can require more power than water at the same flow and head. Ask for absorbed power at the specified duty, and check motor capacity under the actual fluid conditions. For canned motor designs, confirm any minimum-flow or cooling requirements in the supplier’s technical data. Estimates are imperfect; mark assumptions clearly and revisit them when measured operating data becomes available.
Compare the required flow rate and head at each operating point, then check that the motor has adequate power. The examples below are illustrative; actual power depends on pump efficiency, fluid properties, and operating conditions.
Each series uses its own vertical scale, shown on the corresponding axis. Confirm the duty point against the pump curve and verify motor power with the manufacturer before selection.
When comparing canned motor pumps, check the stated editions of API 685 and ISO 15783. API 685 addresses sealless centrifugal pumps for petroleum, petrochemical, and gas services. ISO 15783 covers Class II sealless centrifugal pumps. Confirm that each standard fits your service and purchase specification. A standard name alone proves little.
Ask for a clause-by-clause compliance matrix, including every exception. Check the design pressure, temperature range, materials, inspection records, and applicable performance tests. Review how the containment shell handles the process fluid and pressure. Also examine motor cooling and bearing lubrication arrangements; these details matter when the liquid is hot, viscous, or prone to crystallizing. Not just a logo.
A common review mistake is accepting a general compliance statement without checking its limits. I would compare the submitted documents against the actual operating conditions, including startup and low-flow periods. Some requirements may depend on the agreed scope, so clarify them before approval. The paperwork can look complete. It may still leave a practical gap. Ask who verifies each test, what acceptance criteria apply, and how deviations are recorded.
For a canned motor pump, NPSH is a reliability check, not just a catalog number. NPSHa is the pressure head available at the pump suction; NPSHr is the minimum shown on the pump curve. Keep NPSHa above NPSHr with a suitable margin. Hydraulic Institute guidance treats that margin as application-dependent, so a single rule of thumb can be misleading. ANSI/HI 14.6 defines NPSH3 around a 3% drop in pump head during testing. That is a test criterion, not a cavitation-free operating promise.
Calculate NPSHa using absolute suction pressure, liquid level, vapor pressure, and losses through the suction pipe and fittings. Check the hardest operating case: low tank level, warm liquid, peak flow, and a dirty strainer. Then compare it with the supplier’s NPSHr curve at the actual speed and flow. A spreadsheet can still miss a partly closed valve. I would not treat a small positive difference as comfortable margin, especially when the pumped liquid also cools or lubricates internal components. Verify assumptions with measured site conditions where possible. Small margins matter.
7 Tips for Choosing a Canned Motor Pump?
Match Wetted Materials to Fluid Chemistry, Temperature, and Pressure
Treat every fluid-contacting part as part of the material decision: casing, impeller, rotor sleeve, can, and bearings. A casing that resists corrosion may still pair poorly with a vulnerable sleeve. Check the fluid’s pH, chloride level, solvents, and suspended solids against material data. For example, chlorides can challenge stainless steels, while abrasive particles can wear bearing surfaces. Small details matter.
Temperature changes the picture. Heat can accelerate corrosion and reduce the strength of some metals or polymers. Pressure adds another check: confirm that the selected materials and component thicknesses suit operating and upset conditions. API Standard 685 provides design requirements for sealless centrifugal pumps, but it does not replace a fluid-specific materials review. Ask suppliers for documented compatibility data at actual operating conditions, not just room temperature. A chart may look reassuring. It can still miss a contaminant.
The cost of getting corrosion control wrong is substantial. NACE International’s 2016 IMPACT study estimated global corrosion costs at US$2.5 trillion annually, or 3.4% of global GDP; it also estimated that better corrosion management could save 15–35% of those costs. These are economy-wide figures, not pump-specific predictions. Use them as a reason to review material choices carefully, then verify uncertain cases with corrosion testing or a qualified materials specialist.
| Tip | Fluid or Operating Condition | Materials to Consider | Selection Guidance |
|---|---|---|---|
| 1. Identify every wetted part | Any liquid, including process fluid that may enter the rotor chamber | Casing, impeller, shaft, bearings, rotor can, sleeves, gaskets, and seals must all be reviewed. | Request a complete wetted-material list. A compatible casing alone does not ensure compatibility of bearings, can, or gasket materials. |
| 2. Match materials to the full fluid chemistry | Water, hydrocarbons, acids, alkalis, solvents, or mixed process streams | 316L stainless steel may suit many general services; higher-alloy materials such as nickel alloys may be needed for more aggressive media. | Check concentration, impurities, dissolved gases, and cleaning chemicals. Compatibility can change substantially with fluid composition. |
| 3. Check chloride and pitting risk | Seawater, brines, or chloride-bearing process liquids | Consider chloride-resistant alloys or suitable nonmetallic options where the design permits. | Do not assume 316L is suitable for every chloride service. Temperature, chloride concentration, crevices, and oxygen levels affect corrosion risk. |
| 4. Verify temperature limits | Hot, cold, or temperature-cycling service | Select metals, bearing materials, insulation, and gasket compounds rated for the actual operating range. | Confirm normal, startup, shutdown, upset, and cleaning temperatures. Temperature can accelerate corrosion and reduce the limits of nonmetallic components. |
| 5. Confirm pressure and mechanical suitability | High discharge pressure, pressure surges, or vacuum conditions | Review casing and rotor-can material, thickness, joint design, and allowable stress at operating temperature. | Material choice alone does not establish pressure capability. Check the pump’s rated pressure, temperature derating, pressure transients, and applicable design code. |
| 6. Assess solids, abrasives, and lubrication | Liquids containing crystals, suspended solids, or low-lubricity fluids | Choose bearing and wear-surface materials suited to the fluid’s lubricating properties and particle characteristics. | Check solids size, hardness, concentration, and tendency to settle. Confirm that the fluid can lubricate and cool the pump’s internal bearings as required by its design. |
| 7. Validate compatibility for the actual duty | Continuous operation, intermittent duty, flushing, or frequent cleaning | Use documented material grades and fluid-specific corrosion or compatibility data for all wetted components. | Provide the supplier with fluid composition, concentration, temperature range, pressure, and operating cycle. Confirm selections against current engineering data before purchase. |
Material examples are general guidance, not a guarantee of suitability. Final selection depends on the exact fluid, pump design, operating conditions, and verified compatibility data.
Before choosing a canned motor pump, compare its motor nameplate with the electrical supply at the installation site. Record the required voltage, frequency, and phase, then check them against the available circuit. A small mismatch can cause poor starting, overheating, or reduced performance. Check the voltage tolerance in the technical documentation, too; a nominal reading alone may not tell the whole story. Small details matter. If the pump will use a variable-frequency drive, confirm that the motor and pump are suitable for that operating range.
Frequency affects motor speed and can change the pump’s flow and head. A unit designed for 50 Hz may not perform as expected on a 60 Hz supply, or vice versa. Verify the specified operating frequency before comparing performance figures. Then check the enclosure rating against the actual location: dust, washdown spray, humidity, or outdoor exposure may call for different protection. An enclosure rating does not automatically mean the motor can be submerged. That assumption is easy to make, and worth questioning. Keep a photo of the nameplate and the relevant documentation with the equipment records, so installers can recheck the requirements if the supply or location changes.
