Progressing Cavity (PC) Pump

Progressing cavity (PC) pumps move fluids by trapping liquid between a helical rotor and elastomeric stator, creating sealed cavities that progress axially as the rotor turns. The single-screw design handles viscous fluids, solids up to 3 inches, and provides pulsation-free flow with self-priming capabilities down to 28 feet of suction lift. Flow rates in municipal applications typically range from 5 to 2,000 GPM with heads up to 500 feet. The primary trade-off is stator wear from abrasives and chemicals, requiring replacement every 2-5 years depending on application severity and elastomer selection.

• Waste Activated Sludge (WAS) Transfer: PC pumps handle 1-8% solids WAS from clarifiers to digesters or dewatering, typically 50-500 GPM. Selected for gentle handling that maintains floc structure and prevents shearing. Connected downstream from RAS/WAS splitter boxes, upstream to sludge thickeners or digesters
• Polymer Feed Systems: Diluted polymer solutions (0.1-0.5%) at 5-50 GPM from makeup tanks to process points. Chosen because rotating action doesn't break polymer chains like centrifugal pumps. Feeds directly to flocculation basins, belt filter presses, or centrifuge polymer injection points
• Scum and Grease Handling: Primary clarifier scum at 2-6% solids, 10-100 GPM to digesters or disposal. PC pumps handle stringy, viscous material that clogs other pump types. Takes suction from scum troughs, discharges to scum storage or co-digestion systems

Daily Operations: Monitor discharge pressure (typically 50-150 PSI), flow rate, and motor amps. Adjust VFD speed based on upstream levels or downstream demand. Check for unusual vibration or noise indicating stator wear. Verify suction hopper isn't bridging or cavitating.

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Maintenance: Replace stator every 6-18 months depending on abrasive content and operating hours. Requires confined space entry procedures and lifting equipment for larger units. Lubricate universal joints weekly. PPE includes eye protection, chemical-resistant gloves, and respiratory protection when handling sludge systems. Requires millwright skills for alignment and mechanical assembly.

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Troubleshooting: Decreasing flow with constant speed indicates stator wear - worn stators allow fluid bypass. Excessive vibration suggests rotor/stator misalignment or worn universals. Stators typically last 4,000-8,000 hours in clean applications, 2,000-4,000 hours with abrasive sludge. High discharge pressure with low flow indicates downstream blockage or stator swelling from chemical incompatibility.

• Rotor/Stator Assembly: Single helical rotor turns inside double-helix elastomer stator, creating sealed cavities that progress fluid. Rotors are chrome-plated steel; stators use nitrile or EPDM rubber. Municipal sizes: 2-8 inch rotor diameter, 3-15 foot lengths for 10-1000 GPM capacity
• Drive Train: Variable speed motor (5-50 HP) through speed reducer (10:1 to 100:1 ratios) to maintain 50-500 RPM rotor speed. Lower speeds reduce stator wear and handle higher viscosity fluids
• Hopper/Suction Housing: Oversized inlet (typically 1.5-2x discharge size) prevents bridging of solids. Includes cleanout ports and level switches for automated operation
• Universal Joint: Flexible coupling accommodates rotor wobble and thermal expansion. Requires regular lubrication and replacement every 2-3 years in continuous service

• Flow Rate: 5-2,000 GPM typical municipal range. Biosolids applications: 50-500 GPM most common. Chemical feed: 0.1-50 GPM
• Discharge Pressure: 50-300 PSI standard municipal applications. Biosolids dewatering: 150-250 PSI. Chemical metering: 25-150 PSI
• Suction Conditions: Self-priming to 25 feet dry lift. NPSH required: 3-8 feet typical
• Solids Handling: Up to 40% by volume for thickened biosolids. Raw sludge: 2-6% solids typical. Abrasive solids: <500 mg/L recommended
• Viscosity Range: 1-100,000 cP. Municipal biosolids: 1,000-10,000 cP typical
• Temperature: 32-180°F operating range. Municipal wastewater: 50-85°F typical
• Rotor Speed: 50-720 RPM. Lower speeds for abrasive materials. Biosolids: 100-400 RPM typical
• Stator Life: 2,000-8,000 hours depending on application. Polymer feed: 8,000+ hours. Grit-laden flows: 1,000-3,000 hours
• Efficiency: 65-85% overall efficiency typical. Decreases with wear and higher pressures

• What solids concentration and abrasiveness will the pump handle? Concentrations >6% solids require hard chrome rotors and abrasion-resistant stators. Gritty applications need oversized stator cavities and reduced speeds <200 RPM. Wrong selection leads to premature stator failure within 500-1,000 hours instead of expected 2,000+ hours
• What discharge pressure is required at maximum flow? Pressures >200 PSI require multi-stage units or alternative pump types. Single-stage limit typically 250 PSI. Undersizing causes flow shortfall; oversizing wastes 15-25% energy and increases maintenance frequency
• How will the pump be controlled - VFD or bypass? VFDs enable precise flow control ±2% but cost 30-40% more initially. Bypass control simpler but wastes energy at partial loads. Need process flow variability data and accuracy requirements
• What stator material matches the fluid chemistry? NBR for general wastewater, EPDM for ozone contact, FKM for chemical resistance. Wrong material causes rapid degradation - stator replacement every 500 hours vs. 3,000+ hours with proper selection

• Division 40-30-23 - Progressing Cavity Pumps (primary)
• Division 46-71-13 - Liquid Chemical Pumps (chemical feed applications)

• Material/Equipment Verification: Verify stator elastomer compatibility (Buna-N standard, EPDM for ozone contact), Confirm shaft seal arrangement (mechanical vs. packing)
• Installation Requirements: Rigid mounting foundation (vibration isolation typically not needed), Suction piping support within 6 pipe diameters, Discharge pressure relief valve mandatory
• Field Challenges: Rotor/stator alignment critical during assembly, Drive coupling alignment affects wear rates
• Coordination Issues: VFD compatibility verification required, Lead times: 12-16 weeks standard, 20+ weeks for exotic materials

• Seepex: GmbH series (municipal sludge)
• Moyno: 2000 Series (0.5-500 gpm municipal range)
• NOV Mono: C-range pumps (compact municipal installations)
• Netzsch: NEMO series (food-grade applications, some municipal)
• Seepex and Moyno dominate US municipal market with established service networks. All offer stainless steel wetted parts for municipal applications

• Diaphragm Pumps: Better for high-solids (>8%) applications, 15-25% higher capital cost but lower maintenance
• Lobe Pumps: Preferred for clean water transfer, similar efficiency but 40% higher flow capacity
• Centrifugal with Chopper: Cost-effective for low-head applications (<50 ft), 60% lower capital cost but higher power consumption and maintenance frequency

Stator Selection: Specify one durometer softer than manufacturer recommendation for municipal sludge - extends life 30-40% in typical installations. Manufacturer Relationships: Establish service agreements upfront; stator replacement is specialized work requiring factory training. Cost Savings: Standardize on single manufacturer across facility to reduce spare parts inventory and training requirements.