Cleaning and maintaining sanitary processing conditions are the key reasons customers choose peristaltic pumps, according to John Beahm, Marketing Manager at Watson-Marlow/Bredel (WMB; Wilmington, MA). Peristaltic pumps, which have no valves, seals, or glands, generate pumping force by squeezing elastomeric tubing inside the pump mechanism. Therefore process fluids contact only the bore of the tubing inside the pump, and not the pump internals themselves.
"Peristaltic pumps are unique in that they employ flexible tubing, not metal or plastic internals, to contact process fluids," Beahm told Pharmaceutical Online. "Process fluid contacts only the inside of the tube, which is easily changed, cleaned, or thrown away. This completely eliminates the possibility of cross contamination. I don't know of any other pump type offering this feature."
WMB has developed several proprietary tubing materials, the best-known of which is BioPrene—made from a very finely extruded polymer which reduces the potential for product permeation through the tube or for the tube itself to emit chemicals into the process stream. BioPrene meets Class VI FDA requirements for autoclavability, as well as offering outstanding life (up to 10,000 hrs without servicing).
Bioprene may be pre- or post-sterilized via autoclave, cleaning fluids, or irradiation, before reuse. This leads to one of the peristaltic pump's main selling points: extremely low cost of ownership. "Once you buy them the pumps start paying you back immediately through ease of changing the tube," Beahm said. Specifically, since only the tube contacts the process stream, users need not take the pump apart to clean it. "Even if customers decide to throw the tubing away rather than clean it, it's still a cost-effective way to pump sanitary material because the tubing is inexpensive."
Other manufacturers offer peristaltic pumps, but Watson-Marlow/Bredel claims to provide the widest range of pumps based on flow rate. "Some of our competitors do quite well in different [flow rate] niches," Beahm said, "But we run the entire gamut with regard to flow rate." WMB's lowest-flow pump, used in instruments, provides a flow of 2 mL/min with accuracy to 0.5%. Applications include chromatography and addition of trace nutrients or chemicals for various processes. The firm's highest-flow peristaltic pump, delivering 200 gal/min, is appropriate for almost any large-scale process.
Peristaltic pumps are positive displacement devices, meaning that each time the rotor turns precisely the same amount of liquid is dispensed. Thus, peristaltic pumps are ideal both for metering and dispensing. This capability allows, for example, having a pump and flowmeter in the same unit, which gives rise to interesting control applications where the pump can 'talk,' say, to a pH meter. And since pump speed and flow are linearly related, linear flow is controlled simply by changing the pump speed. Another benefit of peristaltics is very high turndowns. That means the top speed is typically much higher than the pump's average flow speed, which gives operators a very wide range of flow rates available from a single pump. Wide dynamic range facilitates such processes as titrations, where first large quantities, then smaller quantities of liquid must be added to a process.
WMB research and development is intimately connected with customer feedback. "While we haven't necessarily developed specific products based on specific customer requests, we constantly make upgrades and improvements based on what customers want," Beahm said. Many of the long-life, low-service capabilities of WMB's peristaltic pumps, for example, were implemented because customers wanted longer operation and easier maintenance.
One customer-driven application was "weigh dosing," through which a pump interfaces with commercial balances that accept electronic input. Pumps are programmed to respond to a certain weight limit for turning flow on and off. Another such application is the x-y robot, designed to fill hundreds of sample vials in a tray. Beahm said that both these applications resulted from customers telling WMB, "these operations are taking us an awfully long time to do."
"We believe that today customers turn to peristaltic pumps when other pump types have been unsuccessful in producing desired results. Usually the concern is contamination, which we discussed earlier, or maintenance/production down time, which is related to wear on pump internals. Other pump types use metal or PVC internals, so chemical compatibility not always the best. Also, when pumping slurries or granular materials, grains will eventually wear down the pump through abrasive wear. Rubber hoses are inexpensive can be replaced with minimal down time, whereas structural internals cannot.
For more information: John Beahm, Marketing Manager, <%=company%>, 220 Ballardvale St., Wilmington, MA 01887. Tel: 978-658-6168.
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