Peristaltic Pumps in Water and Wastewater

Water is an amazing commodity— a building block of life. Organisms ranging from humans to plants to animals cannot survive without it. Municipalities cannot exist without a readily available water supply, teamed with the ability to consistently deliver it to residences, businesses, hospitals and community centers. Operations in many major industries would halt without water, which is used as an ingredient in thousands of finished products—from food to cosmetics. Water is also used as a cleaning or cooling agent for equipment in industrial applications. In instances such as these, water often becomes wastewater, which must be treated or disposed of. With increased emphasis placed on environmental responsibility, proper wastewater handling and treatment is becoming increasingly crucial. With water playing such a critical role, a need for pumping technology that can efficiently, reliably and safely handle water—from its most pristine state to the soiled variety that flows into a water treatment facility—is paramount. Wastewater can be especially problematic for pumping equipment because it can become fouled with abrasives or solids that can harm pumps, or hazardous materials that must be contained to protect the safety of plant personnel and the environment. This article highlights a pumping technology—positive displacement peristaltic (hose) pumps—that rises to the challenges inherent in handling and treating water and wastewater in municipal and industrial applications.

The Challenge

The design and operational characteristics of peristaltic pump technology, which was patented in 1925 in France, make it a wise choice for water handling—from moving viscous and/or abrasive slurries to transferring water-thin, non-lubricating fluids and shear-sensitive materials. These characteristics make peristaltic pumps ideal for all operations in the water and wastewater industry. Peristaltic pumps satisfy the requirements of these applications because their operation is based on the alternating contraction and relaxation of the hose, forcing the contents to move through the pump and into the discharge piping. A smooth-wall, flexible hose is fitted in the pump casing and is squeezed between shoes on the rotor and inside the pump casing. This rotating action moves the product through the hose at a constant rate of displacement. The hose restitution after the squeeze produces an almost full vacuum that draws the product into the hose from the intake piping. The pump casing is lubricated to cool the pump and lengthen the service life of the shoes and hose. Because the product only contacts the hose and not the internal pump components, this pumping technology is suitable for abrasive and corrosive applications. This pump style maintains excellent volumetric consistency, making it ideal for the strict dosing and 24/7 operating cycles that can be required in wastewater treatment. The pump’s seal-free design makes it dry-run, self-priming and low-slip capable and eliminates any potential leak or contamination points while simultaneously providing superior suction lift. Peristaltic pumps are easy to operate and maintain. The pump’s reversible operation also allows for pumping in both directions. To successfully manage the challenges of water and wastewater handling and treatment, the peristaltic pump’s hose needs to achieve the highest level of material compatibility and reliably deliver the millions of pumping cycles required during its lifetime. Another consideration when selecting a hose material is its fatigue resistance. This trait defines how resistant to failure the hose is as it runs through millions of pumping cycles. A hose material that is susceptible to developing cracks and holes relatively early in its operational life is not as desirable as a material that can reliably handle the demands of the repeated contraction and relaxation of the hose, especially when particulate-laden liquids are being pumped. The reinforced construction of a peristaltic hose and its rubber composition—specially designed for the stresses within it—allow for optimum life cycle and performance.

While peristaltic pumps can be a reliable component in the optimization of water and wastewater operations, one specific pump for lime-dosing applications stands out. Some of the materials of construction and other features discussed in this section are only available on specialized peristaltic pumps. Consult a pump provider for availability.

The sealless design components of peristaltic pump technology

The pumps for lime-dosing feature a seal-free design that eliminates leaks and product contamination, which enables them to handle the toughest water and wastewater pumping applications, from abrasive and aggressive fluids to shear-sensitive and viscous materials. The pumps, which can operate forward or reverse, are self-priming and offer suction-lift capabilities to 9 meters (25.5 feet), as well as the ability to run dry continuously without adversely affecting the pump’s performance. Ductile-iron and steel construction allow the pump to produce discharge pressures as high as 16 bar (232 psi). The pump’s hoses are available in three materials of construction, which were chosen because of their high levels of fatigue resistance:

• Natural rubber—highly resilient with excellent abrasion resistance and strength
• Ethylene propylene diene monomer (EPDM)—high chemical resistance, especially when handling concentrated acids and alcohols
• Nitrile rubber—highly wear resistant to natural-gas-containing products

They have been designed to handle:

• Products with water-like viscosities to viscosities as high as 70,000 centistokes (352,000 Seconds Saybolt Universal)
• Solid particle sizes from 1.5 millimeters to 18 millimeters (0.06 inch to 0.71 inch)
• Soft particle sizes from 1.5 millimeters to 31 millimeters (0.06 inch to 1.22 inches)

These peristaltic pumps can handle product temperatures ranging from 0 C to 70 C (32 F to 158 F) with models featuring an EPDM hose capable of handling maximum temperatures of 80 C (176 F). Optional equipment includes hose-failure detectors, vacuum kits and non-metallic—polypropylene homopolymer (PPH) and polyvinyldine fluoride (PVDF)—inserts.

Conclusion

The water and wastewater industry is one of the most diverse in the global economy. This diversity means that the pumps used in all water and wastewater operations must be nimble and versatile enough to cope with fluids of many different viscosities, temperatures, corrosive levels, toxicities, abrasive natures and particulate levels. These varying product characteristics must also be successfully handled while adhering to strict production quotas and environmental requirements. Peristaltic pump technology has been a leading choice for water and wastewater professionals who know the value of reliable, environmentally friendly, maintenance-free pump operation.