Diaphragm Pumps The Arrival of Diaphragm Pumps as Mainstream Process Pumps
From specialized processes that require system-pressurization pumps, to very flexible flow regimes, to most delicate pumping of fluids/products produced: This article shows that the diaphragm pump is no longer in the fringes of processing but at the heart of the operation to deliver the highest quality product at the greatest yield as efficiently as possible.
In the evolution of pumps, the air-operated diaphragm pump is a more recent technology, if you consider 60 years since its invention recent. This compares with the lobe, centrifugal and gear technologies that were developed more than 100 years ago. Speaking of recent diaphragm-pump developments, the quaternary (four-piston) diaphragm pump, one that is mechanically driven, was invented merely over a decade ago by the founders of today’s Quattroflow Fluid Systems. As such, we see how an even recently entirely new pump class can revolutionize mainstream fluid transfer, in this case, in the biotechnology sector.
But, first, back to air-diaphragm pumps. They were born out of necessity in 1955 thanks to Jim Wilden, namesake of today’s Wilden brand, part of PSG, a Dover company. This pump technology was developed and applied where no other pump was capable of doing the job at the time. In this case, it was the sludge produced in steel mills that needed a pump that was both continually self-/dry-priming and could handle the abuses of particulate-laden sludge. Over time, however, it became clear that the virtues of this technology, such as self-priming, deadheading, low shear and particulate handling, could assist in the transfer of more refined and costly fluid chemistries.
The hygienic industry, in which purity and cleanability are extremely important in the manufacture of biotech, pharmaceutical, food, beverage and personal-care products, is one where refined air-diaphragm pump technology is now playing a prominent role. At first, the air-diaphragm pump was adapted because of its ability to remove thick products from containers for further processing. Today, for example, drum-unloading operations remain a staple application for these pumps.
The sheer number of air-operated diaphragm pump suppliers offering hygienic pump models rivals centrifugal pumps and lobe pumps. Frost & Sullivan estimates that 21 % of the market of diaphragm-operated pumps (air, dosing, motorized) go into the hygienic industry, compared to 12 % for centrifugal and 13 % for lobe pumps on a value basis globally.
As one engineering manager of a large food-processing multinational that is known for its sauces has said: “We would bring air-operated diaphragm pumps into our process designs as a last resort when nothing else would work. Now, we use it as our first pump of choice and consider other pumps if the application does not fit a diaphragm pump.” In this case, because of the high variability of product formulations produced, some very thick, some very thin, high and low flows, with and without big particulates, requires a pump with broad capabilities; a key ability of this type of pump technology.
This trend can be commonly seen. One hygienic sub-segment in which the switch from simply being an unloading pump to a mainstream process pump is very visible is the personal-care/cosmetic industry. Plants with a preponderance of diaphragm pumps in operation are to be found from large multinationals to smaller co-packers. This is especially true in formulation and filling lines that are able to take full advantage of the air-diaphragm pump’s very flexible viscosity, suction and flow operating characteristics. Of course, if an application has needs that cannot be met by a diaphragm pump, such as flow regime, flow rate or discharge pressure, then a suitable pump for these situations is needed.
Some traditionalists will write off the use of an air-diaphragm pump because of the fact that it is powered by air. This stance needs further consideration because the very fact that the pump runs on air that is compressible gives these pumps some process-friendly capabilities that are not achievable by other pumps. For example, enabling production of a product with less thickener since the thickener is not damaged by shear in a pump may trump simple energy usage in value between pumps. Let’s examine these capabilities:
These pumps can easily and automatically achieve a deadhead condition by simply adjusting the air pressure to match the system’s maximum desired deadhead pressure. This is possible without introducing heat or shear to the product, which is a key need in the production process for many hygienic products, such as pumping yeast (live cells) or expensive skin creams. The only other mainstream pump class that can be deadheaded (somewhat) is the centrifugal pump, but these pumps quickly generate considerable heat and shear in deadhead operating conditions and are not a suitable option.
Examples of the benefits of deadhead capability can be found industry-wide beyond the simple protection against broken pump shafts and burst piping. They include:
Certain filter-feeding processes: Certain filters, such as the filter presses found in beverage plants, operate at an ideal pressure to maximize the filtration process. The goal here is that as the filter gets loaded during the process, the operating pressure cannot be exceeded. If it is, the material that is retained in the filter, termed “breaking the filter cake” in the industry, can be pushed through to contaminate the end-product. Such an event is costly. Air diaphragm pumps are a simple safeguard against this.
Filler-feed processes: Certain filler technologies need a stuffing pressure, for example, to feed a volumetric cylinder that later pushes product into the container. The air-diaphragm pump does just that. It charges the system to the desired pressure so when the filler cylinder’s channel opens, product flows in. When it is closed, such as during the container-dispensing process, the diaphragm pump keeps the line pressurized to react quickly during the next opening. If it were not for the air-diaphragm pump, complex control loops with sensors, valves, drive control and automation would be needed. A prominent shaving-cream company did just that replacing a complex pump and pressure control system with a simplified and reliable diaphragm pump charging/feed system for greatly improved reliability and yield.
Shear-sensitive applications benefit even further when fed by air-diaphragm pumps. Two different U.S.-based multinationals that produce personal-care products know this. In one case, problems were experienced with lobe pumps that were causing shearing in the shampoo, which produced foam in the beginning of the production process. The incorporation of air-operated diaphragm pumps both increased the accuracy of the fill with proper feed and also eliminated the foaming issues at startup.
Easily unloading containers from above is an easy match. However, this capability offers much more. Some processes are intermittent. A case in point is centrifuges used to separate products of different densities from fluids. Centrifuges typically need to discharge to atmosphere. Stators in this equipment rotate at more than 2,000 rpm and are heavy because of solid metal construction, which requires a considerable amount of expended energy.
Beckman and Coulter, in their safety training on small centrifuges, give the example that one kilogram at high rotation is equal to an effective equivalent force/weight of 802,000 kg, which, they say, is two jumbo jets! As such, at no time can the discharged material be permitted to back up into the centrifuge and cause an imbalance, which would cause severe damage to the equipment, not to mention the creation a safety hazard. The constant and reliable self-priming of air-operated diaphragm pumps minimizes the risk of product backup into the centrifuge that can be the result of priming issues.
The air-diaphragm pump can be used to move this material reliably and safely away from the centrifuge by self-priming when the material is discharged while not having any corresponding adverse affect on the pump when no material is arriving (dry running). Add in the fact that air-diaphragm pumps can handle the loading of liquids with high solids concentrations; few other pumping solutions that are as simple and reliable are even available.
Centrifuges are one example for equipment that cannot have the discharged product back up into it. There are other critical machines that could have that requirement for best performance, reliability and safety.
Low Shear Generation
Many technologies claim to be low shear but this is relative and subjective detail. For example, many PD pumps are considered low shear. However, if operating above low pressure, with low viscosity products, then they are actually high shear.
When pumping low-concentration yeast (living cells) in a water-based solution through lobe or gear pumps, the amount of product actually being pumped can be less than 30 % of the theoretical displacement of the pump (Consider 1-cps product, 100-psi discharge pressure). That means that 70 % of the fluid is actually slipping past the clearances of the pump. This represents considerable product shear.
The amount of shear energy can be seen in the motor horsepower required to overcome the slip. Shear, such as that produced by improper pump selection or other process problems, can have a significant impact on product quality and ultimate process efficiency/profitability. Manufacturers of products that have thickeners like starch, such as pudding or light mayonnaise or tomato paste for tomato-based products, know that by reducing shear during processing, they can reduce the quantity of these expensive ingredients in their formulations. This is discovered by accident many times when processing the product in a new process that happens to be lower shear and makes a product “too thick”. Discussed previously is how diaphragm pumps operate with little slip because the fluid is either pumped forward or checked by the check valves that are used to prevent slip.
From specialized processes that require system-pressurization pumps, to very flexible flow regimes, to most delicate pumping of fluids/products produced, we see that the diaphragm pump is no longer in the fringes of processing but at the heart of the operation to deliver the highest quality product at the greatest yield as efficiently as possible.