Not surprisingly, food safety has always been a top concern for the companies that produce processed foods and beverages. So, it goes without saying that this is a precise industry, one that requires the highest standards in hygienic and sanitary production processes. Despite this emphasis on food safety, there still have been a number of food-safety scandals that have combined to give the consuming public reduced trust in the safety that the food-and-beverage industry can provide. For example:
- The United States Food & Drug Administration (FDA) issued an average of 188 Class I (the most serious) food recalls over the five-year period from 2002-06. A Class I recall is one in which there is a reasonable probability that the use of, or exposure to, a product will cause serious adverse health consequences, or death.
- The European Union Risk Analysis Information Network (EU-RAIN), which consists of 20 research institutions and consumer organizations from Europe and North America, has reported that between 10 percent and 30 percent of the population in industrialized countries suffers from food-borne illnesses on an annual basis
- A survey by the Food Marketing Institute—“U.S. Grocery Shopper Trends 2007”—showed that consumer confidence in the safety of the food supply has dropped dramatically. After hovering in the 80th percentile for several years, it dropped to 66 percent in 2007, the lowest level since 1989. By comparison, only a decade ago what was in a product, how good it was for you, its production process and where it came from barely registered with consumers.
Of course, there are stringent standards and regulations in place that have been designed to guarantee the safe manufacture of all types of foods and beverages. The FDA’s Hazardous Analysis and Critical Control Point (HACCP) “is a management system in which food safety is addressed through the analysis and control of biological, chemical and physical hazards from raw material production, procurement and handling to manufacturing, distribution and consumption of the finished product.”
HACCP is an over-arching system that has been designed for use in all segments of the food industry, from growing, harvesting, processing, manufacturing, distributing and merchandising, to preparing food for consumption. Within the HACCP parameters, there are precise requirements for the production of specific products. For example: the Good Manufacturing Practices program addresses the implementation of food-safety systems during manufacture; the strictures of the National Advisory Committee on Microbiological Criteria for Foods provide guidance regarding the microbiological safety of foods; and 3A certification formulates standards for the sanitary production and handling of dairy products.
Finding The Right Solution
Food production is a 24-hour-a-day, 365-day-a-year operation with various types of pumping equipment needed to keep the process running smoothly. As such, the HACCP system specifies a number of questions in the areas of equipment design and use that must be addressed before that equipment can be introduced to the production process:
- Does the equipment provide the time-temperature control that is necessary for safe food?
- Is the equipment properly sized for the volume of food that will be processed?
- Can the equipment be sufficiently controlled so that the variation in performance will be within the tolerances required to produce safe food?
- Is the equipment reliable, or is it prone to frequent breakdowns?
- Is there a chance for product contamination with hazardous substances?
- To what degree will normal equipment wear affect the likely occurrence of a physical hazard in the product?
- Can the facility and equipment be easily cleaned and sanitized to permit the safe handling of food?
This means that all equipment used in the production of foods and beverages should be constructed and installed according to sanitary-design principles with preventive-maintenance and calibration schedules established and documented. Also, all procedures for cleaning and sanitation of the equipment and the facility should be written and followed with a master sanitation schedule put in place.
Moving in the direction of the HACCP assessments, the air-operated double-diaphragm pump—which was invented in 1955 in California by Jim Wilden—has evolved to become one of the most hygienic pump types in the industry. The design has been refined to take advantage of the fact that they do not contain any mechanical seals and rotating parts. This elimination of any nooks and crannies, as well as the use of integral-piston diaphragms that only have PTFE as the exposed surface help the cleanability of the liquid path of this pump. This design closely matches that of a diaphragm valve while actually nearing the cleanability of a simple piece of sanitary tube. In fact, the European Hygienic Engineering & Design Group (EHEDG) certification for cleanability requires that the cleanability of the pump be matched to the cleanability of a smooth tube of the same diameter as the inlet/outlet of the pump.
While Wilden, who named his resulting operation the Wilden® Pump & Engineering Company and based it in Grand Terrace, CA, originally developed his AODD pumps for use in harsh, brutish environments, over the years the technology and materials of construction have been refined. These refinements now give the pumps the versatility and sensitivity of operation for a number of applications in industries that require hygienic and sanitary operating conditions.
How AODD Pumps Work
AODD pumps are classified as reciprocating, positive-displacement-style pumps. The pump operates by displacing fluid from one of its two liquid chambers upon each stroke completion. To operate the AODD pumps require a given amount of pressure (measured in pounds per square inch) and air volume (measured in cubic feet per minute) to deliver the proper amount of fluid.
The simple genius of the AODD pump design means that there are only a few wetted parts that are dynamic: the two diaphragms, which are connected by a common shaft, the two inlet valve balls and the two outlet valve balls. The diaphragms act as a separation membrane between the compressed air supply and the liquid. Driving the diaphragms with compressed air instead of the shaft balances the load on the diaphragm, which removes mechanical stress from the operation and extends diaphragm life. This also allows the valve balls to open and close on the valve seats, which direct liquid flow. This simple design and operation makes it easy for the operator to find the correct pressures and flows to optimize its operation.
More specifically, the pump begins operation when the air distribution system directs the air supply to the right air chamber and back side of the diaphragm. This moves the diaphragm away from the center block and toward the liquid chamber, in the process pulling the opposite diaphragm inward. This means the opposite diaphragm is now on its suction stroke. At the same time, atmospheric pressure forces fluid into the inlet manifold, forcing the inlet valve ball off its seat. This allows liquid to move past the inlet valve ball and into the liquid chamber.
When the pressurized right liquid chamber reaches its liquid capacity, the air valve redirects compressed air to the back side of the opposite diaphragm. This forces that diaphragm away from the center block while pulling the right diaphragm toward the center block. This closes the inlet valve ball on the opposite side while lifting the discharge valve ball off its seat and forcing the liquid to flow through the discharge manifold. The process is repeated for the opposite side, with the liquid chamber filling, the forced air redirecting the diaphragms and the created pressure forcing the discharge valve ball off its seat as the liquid moves through the discharge manifold.
As the pump reaches its original starting point, each diaphragm has gone through one suction and one discharge stroke, which constitutes one pumping cycle.
Pumps Options For Applications
Well-designed turnkey process solutions are best served when product fluid-transfer processes occur without problems. For best results, the engineer must find the best match between the process requirements and the pump technology employed for this service. The diaphragm pump, now in its evolved sanitary design, is the new option for a processor’s fluid-transfer arsenal.
The unique performance characteristics of diaphragm pumps lend themselves to applications in the food-and-beverage industry that have traditionally not been handled well in some cases by other pump technologies.
These characteristics include:
- A “duality” performance nature where a positive-displacement pump employs “dead heading” performance of a centrifugal pump
- Complete absence of mechanical seals
- Dry priming with strong suction lift
- High turn-up/turn-down ratios for application flow flexibility
- Medium to high flow accuracy with highly variable process conditions
To see how the diaphragm pump fits in to compliment other pumps, consider this example. A centrifugal pump is generally accepted as the best solution for pumping a thin product like water or juice. In contrast, a positive-displacement pump, like a lobe pump, would handle thick, shear-sensitive products. However, what if this viscous material—which is initially a candidate for a lobe pump—must be pumped out of the top of a tote (dry-priming need), be seal-less (mechanical) and be subjected to possible frequent dead heading? On the flip side, how about a thin fluid that would be a candidate for a centrifugal pump but require extremely low shear, offer precise flow and not use mechanical seals? In both cases, an alternate pumping solution provided by the diaphragm pump would be appropriate.
Application examples that benefit from this diaphragm pump “duality” (positive displacement with constant pressure/dead-heading performance) and other characteristics are:
- Product filler feeding — Many fillers need to be stuffed to provide proper fill volumes. Diaphragm pumps and constant pressure/dead-heading capability charges the filler with the needed pressure without use of complex controls, gravity-feed tanks, surge tanks, or recirculation lines. This cleans the system, reduces HACCP concern points and improves reliability.
- Batch process metering — When batching ingredients into tanks, some processes benefit from using load cell/diaphragm pump proportioning of ingredients into tanks. As diaphragm pumps can start and stop (and deadhead) at will without adverse effects, they are a good option here.
- Ingredient unloading — Self-priming, strong suction lift, and risk of dry run are applications traditionally best handled with AODD pump. So, whether unloading railcars, trucks, silos, drums, or bins, the diaphragm pump does the best job in ensuring a reliable operation that best recovers product from the source vessel.
- Handling of shear-sensitive and/or large particulates in thick or thin fluids — among pump options, diaphragm pumps offer some of the most liberal flexibility in handling variations in product characteristics. Processors benefit by reducing the number of specialized pumps needed for targeted applications to a broad array of applications handled by fewer types and sizes of pumps.
- Pressure-limiting applications — some types of filters and other processes must control maximum system pressures. The diaphragm pump can be set to not surpass that maximum system pressure without requiring relief or other sophisticated pressure control systems.
Jim Wilden designed his first AODD pump to handle demanding applications that required a robust design. More than a half century later, the time-tested operation of Wilden air-operated double-diaphragm pumps is still setting the standard for a wide range of industries that require the efficient, timely, cost-effective and maintenance-friendly pumping of a wide variety of liquids and other substances.
This is especially critical in the manufacture of foods and beverages, in which preventing food poisoning incidents—which are costly not only in a monetary sense, but also in lost or damaged reputation—is a key focus of the food-safety system. Wilden’s Saniflo? Hygienic Series AODD pumps meet the sanitary requirements of this critical process and provide the peace of mind, return on investment, higher yields and minimized product degradation that are necessary for a successful, safe operation.
Wallace Wittkoff can be reached at (502) 905-9169 or [email protected]. PSG is comprised of six leading pump companies—Wilden®, Blackmer®, Griswold™, Neptune™, Almatec® and Mouvex®. You can find more information on PSG at www.pumpsg.com.
