Watson-Marlow Peristaltic Pumps

Two green Watson-Marlow peristaltic pumps with digital displays and control buttons sit on a reflective surface, surrounded by stainless steel pipes and equipment in a laboratory or processing facility.

Watson-Marlow peristaltic pumps have emerged as a cornerstone technology in modern wastewater treatment facilities, offering unique advantages in handling challenging fluid transfer applications. These pumps excel in managing corrosive chemicals, abrasive slurries, and sensitive biological materials common in wastewater processing.

Watson-Marlow Fluid Technology Solutions, headquartered in Falmouth, Cornwall, in the United Kingdom, is part of Spirax Group and is one of the best-known names among top peristaltic pump manufacturers. For water and wastewater utilities, its most relevant product families are the Qdos chemical metering pumps, the Bredel heavy-duty hose pumps, and the Watson-Marlow cased and OEM tube pumps used for sampling and laboratory duties.

Operating Principle

The pump operates through a simple yet effective mechanism: rollers compress a flexible tube in a rotating motion, creating a vacuum that drives fluid movement. This design eliminates fluid contact with mechanical components, ensuring contamination-free operation and minimal maintenance requirements.

Strictly speaking, the pump does not rely on a vacuum to move fluid. Peristaltic pumps are positive displacement machines: each roller or shoe squeezes the tube or hose closed and pushes the trapped volume toward the discharge, and as the tube springs back to its original shape behind the roller, it creates the suction that draws in the next volume. Because the tube itself acts as the seal, the pump can run dry without damage and can self-prime, with suction lifts of several meters typical depending on tube material and pump model.

Watson-Marlow Product Families for Water and Wastewater

Qdos Chemical Metering Pumps

Qdos pumps use a replaceable cartridge pumphead (ReNu) instead of loose tubing, so the pumping element can be changed without tools and without operator contact with the chemical. The range covers flows from a few milliliters per hour up to roughly 120 L/h, with maximum discharge pressures of up to about 7 bar (roughly 100 psi) depending on the model, which suits most coagulant, polymer, pH adjustment, and hypochlorite dosing duties. Because the pumping action is not disrupted by gas bubbles, Qdos pumps are widely used for sodium hypochlorite, which off-gasses and can cause vapor locking in diaphragm metering pumps.

Bredel Hose Pumps

Bredel pumps use a reinforced rubber hose compressed by shoes rotating in a lubricant-filled casing. They handle discharge pressures up to 16 bar (about 230 psi) and are used for thickened and digested sludge, lime slurry, grit-laden flows, and dewatering feed, where abrasive solids would quickly wear the internals of progressing cavity or centrifugal pumps.

Tube Pumps for Sampling and Laboratory Duties

Watson-Marlow’s cased tube pumps (500, 600, and 700 series) and OEM pumpheads cover low-flow transfer, sampling, and analyzer feed. They accept a range of tubing materials, including Marprene thermoplastic elastomer, Pumpsil silicone, Bioprene, and GORE Style 100 PTFE-lined tubing, so the tube can be matched to the fluid being pumped.

Key Applications in Wastewater Treatment

Chemical Dosing

  • Precise metering of flocculants and coagulants
  • Controlled addition of pH adjustment chemicals
  • Accurate dispensing of disinfectants

Sludge Transfer

  • Handling of primary and secondary sludge
  • Transfer of thickened and activated sludge
  • Management of return activated sludge (RAS)

Sampling and Analysis

  • Automated sample collection
  • Laboratory feed systems
  • Process monitoring

Technical Advantages

  1. Superior Accuracy
    • Flow rates from microliters to hundreds of liters per minute
    • Repeatability typically within ±1%
    • Flow largely independent of discharge pressure within rated limits
  2. Low Maintenance Requirements
    • Only the tube requires periodic replacement
    • No seals, valves, or check valves to maintain
    • Reduced downtime and operating costs
  3. Chemical Resistance
    • Multiple tube materials available (Marprene, GORE, LoadSure)
    • Suitable for aggressive chemicals and high-solid content fluids
    • No cross-contamination between batches

Limitations and Selection Considerations

Peristaltic pumps are not the right choice for every duty. Engineers evaluating Watson-Marlow equipment should weigh the following:

  • Tube and hose wear: The pumping element is a wear part, and its life ranges from a few hundred to several thousand hours depending on speed, pressure, temperature, and the fluid. Replacement elements are the main recurring cost.
  • Pulsating flow: Each roller pass produces a pulse. Where smooth flow matters, such as upstream of flowmeters or static mixers, pulsation dampeners or multi-roller and twin-channel pumpheads may be needed.
  • Pressure limits: Tube pumps generally operate at lower discharge pressures than hose pumps. High-pressure injection points may require a Bredel hose pump or a different pump technology.
  • Chemical compatibility: The tube or hose material must be compatible with the chemical and its temperature. Always check the manufacturer’s chemical compatibility guidance before selecting a material.
  • High-flow clean water: For large volumes of clean water, centrifugal pumps are usually smaller and less expensive. Peristaltic pumps are best suited to metering, sludge, abrasive, and shear-sensitive duties.

Environmental Benefits

  • Lower energy consumption compared to traditional pump technologies
  • Reduced chemical waste through precise dosing
  • Minimal environmental impact from maintenance activities
  • Extended equipment lifetime reducing resource consumption

Integration Features

  • SCADA compatibility for remote monitoring and control
  • Variable speed drives for flow rate adjustment
  • Multiple tube sizes for different flow requirements
  • Optional pressure monitoring systems
  • Automatic fail-safe mechanisms

Cost Effectiveness

  • Reduced chemical consumption through accurate dosing
  • Lower maintenance costs versus traditional pump types
  • Extended tube life through optimized roller design
  • Minimal spare parts inventory requirements
  • Quick tube replacement reducing downtime

Future Developments

Watson-Marlow continues to innovate in the wastewater sector, focusing on:

  • Smart monitoring capabilities
  • Energy efficiency improvements
  • Advanced materials for tube construction
  • Integration with Industry 4.0 technologies
  • Enhanced automation features

Operation and Maintenance Tips

Tube or hose replacement is the single most important maintenance task. Plants that log run hours and replace elements on a schedule, rather than waiting for failure, avoid most chemical leaks and unplanned downtime.

  • Keep at least one spare tube, cartridge, or hose for each critical pump, since supply lead times can exceed element life.
  • Use leak detection or hose failure detection options where fitted, and route pump drains to secondary containment for hazardous chemicals.
  • On Bredel pumps, check the casing lubricant level and condition at every hose change.
  • Verify dosing accuracy with a drawdown test after each tube or cartridge change.
  • Run pumps at the lowest speed that meets demand; tube and hose life improves significantly at lower speeds.

Frequently Asked Questions

What are Watson-Marlow peristaltic pumps used for in wastewater treatment?

They are most often used for chemical metering (coagulants, polymers, pH adjustment chemicals, and sodium hypochlorite), for transferring thickened or digested sludge and abrasive slurries, and for automated sampling and analyzer feed. Qdos pumps typically handle dosing, while Bredel hose pumps handle sludge and slurry.

How often do the tubes need to be replaced?

Element life depends on pump speed, discharge pressure, temperature, and the fluid, and can range from a few hundred to several thousand operating hours. Tracking run hours and replacing tubes or hoses on a planned schedule is the most reliable way to prevent unexpected failures.

Can Watson-Marlow pumps handle sodium hypochlorite?

Yes. Hypochlorite releases gas bubbles that can cause vapor locking in diaphragm metering pumps, but a peristaltic pump continues to deliver flow because the tube compression pushes gas and liquid through together. The tube or cartridge material must still be selected for hypochlorite compatibility.

What is the difference between a Qdos pump and a Bredel pump?

Qdos pumps are compact metering pumps with a sealed cartridge pumphead, designed for accurate chemical dosing at low flows. Bredel pumps are heavy-duty hose pumps with a lubricated casing, designed for higher flows, higher pressures, and abrasive or high-solids fluids such as sludge and lime slurry.

Conclusion

Watson-Marlow peristaltic pumps represent a crucial technology in modern wastewater treatment, offering reliability, precision, and cost-effectiveness. Their unique design and versatility make them an ideal choice for facilities seeking to optimize their operations while maintaining high environmental standards.