Split-case Centrifugal Pump

Split-case centrifugal pumps are high-capacity workhorses designed for moving large volumes of water in municipal treatment facilities. The pump casing splits horizontally, allowing easy access to the impeller and internal components without disconnecting piping. A rotating impeller accelerates water radially outward, converting rotational energy into pressure head. These pumps typically deliver 500-15,000 GPM at heads ranging from 50-400 feet, making them ideal for raw water intake, high-service pumping, and effluent discharge applications. The primary trade-off is their substantial footprint and higher initial cost compared to smaller end-suction pumps.

• High Service/Finished Water Pumping: Split-case pumps deliver treated water from clearwells to distribution systems at 500-5,000 GPM, selected for their high efficiency (82-86%) and ability to handle variable demand. They connect downstream from clearwell outlets with suction piping 12-36" diameter, pumping through 8-24" discharge headers to distribution mains

• Raw Water Intake: These pumps lift water from rivers/lakes to treatment plants at 1,000-8,000 GPM, chosen for reliability with debris-laden water and ability to handle seasonal level variations up to 40 feet. Intake structures feed 16-48" suction lines, with discharge through 12-36" force mains to treatment headworks

• Booster Pumping: Split-case units maintain system pressure in elevated zones at 200-2,000 GPM, selected for constant-speed operation and minimal maintenance requirements. They connect to distribution mains via 6-20" suction piping, discharging through 4-16" lines to pressure zones or storage tanks

Daily Operations: Operators monitor discharge pressure, flow rate, motor amperage, and bearing temperatures during routine rounds. Typical parameters: 80-110% of design flow, motor current within 10% of nameplate, bearing temperatures below 180°F. Adjustments limited to valve throttling since most units run at fixed speed.

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Maintenance: Quarterly bearing lubrication and coupling alignment checks. Annual mechanical seal inspection and impeller clearance measurement. Requires confined space entry procedures for wet pit access, standard electrical lockout/tagout, and hearing protection. Maintenance staff need basic mechanical skills and torque wrench operation for 100-500 ft-lb bolting.

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Troubleshooting: Cavitation damage appears as pitting on impeller leading edges, indicated by noise and vibration increases. Bearing failure shows gradual temperature rise over 2-4 weeks before catastrophic failure. Mechanical seal leakage typically develops slowly with 6-month warning period. Expected service life: 15-20 years for pump, 20,000-40,000 hours for motor.

• Split Casing: Two-piece volute housing allows maintenance without disconnecting piping. Cast iron or ductile iron construction for municipal service, with bronze-fitted versions for corrosive conditions. Sizes range 4"-24" suction, 3"-20" discharge for 200-8,000 GPM capacity

• Impeller: Single-suction design with 6-12 vanes provides 50-400 feet of head. Bronze or 316SS construction, dynamically balanced. Diameters 8"-36" with trimming capability for performance adjustment within 10% of BEP

• Shaft and Bearings: Chrome steel shaft with sleeve bearings (oil-lubricated) or anti-friction bearings (grease-lubricated). L10 bearing life 40,000+ hours at rated conditions. Shaft deflection limited to 0.002" at impeller

• Mechanical Seal: Single or double cartridge seals rated for 150-300 PSI. Silicon carbide faces with Viton elastomers standard. Expected life 3-5 years in clean water service, 1-2 years with raw water applications

• Flow Rate: 200-15,000 GPM typical municipal range. Size for maximum day demand plus fire flow requirements. Standard sizes: 4", 6", 8", 10", 12", 16", 20", 24" discharge

• Total Dynamic Head (TDH): 50-400 feet typical. Calculate static lift plus friction losses plus residual pressure requirements. Account for worst-case system conditions

• Net Positive Suction Head Required (NPSHr): Typically 8-25 feet depending on specific speed. Must maintain 3-foot minimum margin above NPSHr at all operating points

• Efficiency: Target minimum 80-85% at best efficiency point (BEP) for pumps >100 HP. AWWA standards require efficiency curves and power consumption data

• Motor Size: 10-2000 HP range for municipal applications. Size for non-overloading across entire pump curve, typically 110-115% of BEP power

• Suction Specific Speed: Keep below 8,500 (US units) to avoid cavitation issues. Critical for reliable operation

• Operating Speed: Standard 1,180 or 1,780 RPM with 60 Hz motors. Higher speeds increase maintenance requirements but reduce initial cost

• Materials: Cast iron volute standard for potable water. 316 SS trim minimum for wastewater applications

• Single vs. Dual Suction Configuration? Dual suction reduces NPSHr by 15-20% and provides better hydraulic balance, but increases footprint and cost by 20-30%. Choose dual suction for flows >2,000 GPM or when NPSHa is marginal (<15 feet). Single suction acceptable for smaller flows with adequate suction conditions

• Horizontal vs. Vertical Split Case? Horizontal split allows easier maintenance access to impeller and wear rings without disconnecting piping. Vertical split reduces floor space by 40% but requires overhead clearance for maintenance. Choose horizontal for flows >1,500 GPM where maintenance frequency justifies accessibility

• Variable vs. Constant Speed Operation? VFD operation saves 20-40% energy costs for variable demand systems but adds $15,000-50,000 initial cost plus complexity. Justify VFDs when flow varies >30% from design or when multiple pumps operate in parallel. Requires harmonic analysis and motor insulation class considerations

• Pump Curve Selection - Steep vs. Flat? Steep curves (high specific speed) provide stable operation with varying system resistance but limit turndown capability. Flat curves allow better parallel operation but may surge with throttled discharge. Choose based on system head curve analysis and control strategy

• Primary: Division 40-05-23 - Centrifugal Water Pumps

• Secondary: Division 40-05-13 - Disinfection and Fluoridation Equipment Pumps (for chemical feed applications)

• Split-case pumps span multiple water system applications requiring specific material and performance requirements per application

• Material/Equipment Verification: Verify impeller material matches water quality (bronze vs. stainless), Confirm mechanical seal compatibility with chlorinated water, Check motor efficiency meets utility rebate requirements

• Installation Requirements: Foundation design for 150-200% pump weight, Minimum 10 pipe diameters straight suction piping, Crane access for maintenance

• Field Challenges: Alignment sensitivity requires precision millwright work, Grouting cure time affects startup schedule

• Coordination Issues: VFD compatibility verification, SCADA integration requirements, 16-20 week lead times typical

• Flowserve - Model 3196 series dominates municipal high-service and raw water applications

• Sulzer - CPT series popular for water treatment plants 5-50 MGD

• KSB - Omega series widely specified for municipal booster stations

• Grundfos - CR series for smaller municipal applications under 10 MGD

• All maintain extensive municipal reference lists and local service networks

• Vertical Turbine Pumps - Preferred for deep well applications or limited floor space; 15-25% higher cost but eliminates priming issues

• End-Suction Pumps - Cost-effective for flows under 500 GPM; 30-40% less expensive but limited efficiency

• Submersible Pumps - Ideal for wet well installations; similar cost but eliminates dry-pit construction requirements and reduces noise concerns

Establish relationships with local manufacturer reps early - they provide free application engineering and can expedite warranty issues. Specify identical backup pumps to simplify maintenance training and spare parts inventory. Consider factory acceptance testing for critical applications over 1000 GPM. Negotiate extended warranties beyond standard one-year coverage, especially for continuous-duty high-service applications where downtime costs exceed premium.