In recent years, process engineers have increasingly turned to peristaltic pump technology for metering highly caustic and corrosive chemicals. Peristaltic pumps are especially suited to dosing, metering and transferring chemicals—such as hydrochloric acid, sodium hydroxide, sodium hypochlorite and sulfuric acid.
In addition, new peristaltic pump technology is available that is designed specifically for chemical metering in industrial markets. These high-performance pumps accurately meter chemicals without valves or ancillary equipment, keeping costs minimal. In fact, the total cost of ownership is less than that of a typical solenoid or stepper-driven diaphragm pump.
New Peristaltic Pumps Meet Key Selection Criteria
Process engineers face a number of challenges. They must find a pump that withstands chemical attack, runs reliably, meters accurately to optimize chemical usage and is quick and simple to maintain and operate. Meeting all these requirements, the latest peristaltic pumps help plants reduce life-cycle costs and drive gains in process efficiency.
With no valves in the pump to clog, leak or corrode, the new peristaltic pumps can safely and securely handle fluids that are caustic, abrasive, viscous, shear-sensitive, gaseous or slurries. It can also pump fluids that contain suspended solids. The fluid is fully contained within the tubing, eliminating any risk of cross contamination. Such chemical process containment, in combination with accurate and linear flow, helps reduce chemical use, providing cost savings.
The pump’s range generates flow rates up to 7.9 gallons per minute at 100 psi, with speed control of 1,600:1 in analogue mode. The pump also accepts 4-20 mA input and output analog signal control.
The new technology boosts process efficiency by providing accurate, repeatable and linear flow performance, even when transferring difficult fluids with varying pressure, viscosity and solid content. Potential applications include:
- Disinfection of drinking water
- pH adjustment of drinking water
- pH adjustment of industrial process water
- Flocculation, industrial cooling water preparation
- Reagent dosing in mineral processing and paper colorants
Simple Operation
Based on the physiological principle of peristalsis, a term referring to the alternating contraction and relaxation of muscles around a tube (for example, the throat or intestine) to induce flow, a peristaltic pump’s operation is elegantly simple. A flexible tube or hose element is compressed between rotating rollers or shoes and a track. Between each roller pass, the tube or element recovers to create a vacuum and draw in fluid.
It is well documented that acids, caustics and solvents attack the valves, seals, stators and moving parts of diaphragm and progressive cavity pumps, causing disruptive downtime and high life-cycle costs. By contrast, the use of peristaltic pumps allows engineers to mitigate these costs because they contain no valves, seals or glands and have no mechanical parts contacting the product stream. The fluid only contacts the inside of the hose or tube, which is a low-cost, low-maintenance and easily-serviceable component.
Hose and tube materials, which in the past were the only prohibitive factor against the widespread adoption of peristaltic pumps for caustic chemical applications, are now available in different elastomers, formulated specifically to balance long mechanical pumping life with sustained resistance against concentrated acids, bases and solvents.
For example, chlorosulfonated polyethylene (CSM), an elastomer available for hose pumps, can handle toluene and other corrosive solvents that are used to manufacture certain products—such as gaskets, aerosol paints, lacquers, paint strippers, adhesives, cosmetics, perfumes and anti-freeze.
Some of the latest chemical-duty elements are capable of thousands of hours of continuous service operating at flow rates up to 350 gallons per minute and 282 psi. Furthermore, peristaltic pumps have the ability to self-prime, dry-prime and self-clean. They are also reversible to dislodge blockages or drain lines.
The lack of valves makes peristaltic pumps attractive to industries such as paper and pulp. For instance, one peristaltic pump is being used to handle sodium hydroxide for bleaching pulp and disinfecting water at a paper mill.
A 350-gallon-per-minute hose pump
Precise Metering
The inherent accuracy of positive displacement pumps is another reason that they are chosen whenever exact chemical metering or dosing is required. In peristaltic pumps, where metering accuracy is better than 1 percent, flow is proportional to pump speed. Complete tube element closure gives the pump its positive displacement action, preventing flow drop or erosion from backflow and eliminating the need for check-valves, which are typically the primary source of any metering inaccuracy.
Accuracy is particularly important at power plants, as demonstrated by a power generation servicing company that uses peristaltic pump technology to meter 65 gallons per minute of sulfuric acid when cleaning power plant condensers—driving the pH down to less than 4.0 to break down scale. Precise control of acid flow is necessary to ensure that, after scale is dissolved, the discharge to the municipal wastewater system will have a neutral pH.
With regard to turndown ratio, a high-quality peristaltic pump is capable of a flow range greater than 2,000:1 simply by controlling rotor speed. With the added versatility of integrating different tube sizes into a single pump, flow range can expand to 1,000,000:1. Diaphragm pumps are normally limited to 20:1.
New Pump Head Technology
An interesting feature of the new peristaltic tube pump technology is a new pump head—a sealed, single component, no tools maintenance element that is at the core of the pump range. This ensures the delivery of accurate, linear and repeatable flow for fluids of wide-ranging viscosities. It also maximizes valuable process uptime by facilitating quick and easy pump head removal and replacement. There is no need for tools, training or maintenance technicians. The contained pump head design also eliminates safety concerns.
Low Life-Cycle Costs
While the initial cost of a peristaltic pump can be slightly higher than other positive displacement pumps, a quick assessment of life-cycle costs quickly tips the scale in favor of peristaltic pumps. For instance, no seals, ball valves, rotors or stators need replacement, and hose/tube replacement usually takes only a few minutes. The low-cost tube or hose can be replaced in-situ and without special tools or skills, making the process extremely economical in comparison with conventional positive displacement pumps where replacement parts can cost up to 75 percent of the pump’s initial purchase price and take several hours to fit.
For example, the new pump technology delivers flow rates up to 7.9 gallons per minute at 100 psi, while maintenance intervals are up to six months, at typical usage, reducing the impact of downtime.
Another added cost is the need for a separate control panel or variable frequency drive to achieve variable flow metering, with the incremental cost if high turndown is required. Peristaltic pump manufacturers, however, build high turndown, closed-loop speed control capability and expansive I/O connections for DCS, SCADA and PROFIBUS systems into standard pumps for simplified integration.
Process-duty pumping is being taken to the next level with a new, integrated PROFIBUS networking capability that has been added to a peristaltic pump. With two-way, real-time communications, the new technology offers increased diagnostic capability and faster response, helping optimize process control and minimize plant downtime.
Pumping Abrasive Fluids
Frequently, fluids contain corrosive and abrasive material. Peristaltic pumps stand up well to the challenge, as a U.S.-based construction product manufacturing plant can verify. A peristaltic hose pump was used in the manufacture of fiber cement siding products. The cement mixture had little effect on the hose, despite being highly abrasive and strongly alkaline.
Peristaltic pumps are also used for other abrasive fluids, including lime slurry and underflow in mining operations, alum in wastewater treatment and titanium dioxide for pigmented inks and paints.
In contrast with peristaltic pumps, abrasion takes a toll on other positive displacement pumps. Abrasive fluids may cause the erosion or clogging of valves in diaphragm pumps. The same effect in progressive cavity pumps widens clearances between the rotor and stator, which may cause internal slip.
A Growing Choice
The advantages peristaltic pumps offer mean that they represent a rapidly growing percentage of the positive displacement pump market. Plant managers tasked with reducing pump life-cycle costs embrace the functionality and benefits of peristaltic pumps, which are fast becoming the first choice for chemically aggressive and abrasive applications.