MATERIALS HANDLING
The operating principle of Blackmer sliding vane pumps ensures volumetric consistency through a number of self-adjusting vanes that slide in and out of the pump rotor as it turns, creating chambers that carry the same amount of fluid to the discharge port
It wasn’t until the early 2000s that seal-less pump technology had evolved to the point where it could claim to be both a pain-point resolver and totally leak-free. A change in the mindset of the user also helped – leak- free pumps were not just being used when handling hazardous materials, they were being used for the handling of basic liquids such as water. Tis mindset changed because users had become less willing, or capable, of accepting or dealing with seal failures than they were 50 years ago. In other words, even a so-called “nuisance” water leak would require the pump to be taken offline, which would result in expensive downtime and maintenance costs. Te solution: pivot to a seal-less leak-free pump that would never (theoretically) need to be maintained or repaired because of a leak incident.
Tis combination of change in mindset and the now field-proven capabilities of seal- less pumps has turned the pump industry on its head. Today, after steady growth over the past 15 years, the global seal-less centrifugal pump market is valued in excess of US$4.5 billion. In fact, sales of seal-less ANSI centrifugal pumps have the potential to eclipse sealed-pump sales in the coming years. But despite all that, there remain challenges that seal-less pumps must overcome.
THE CHALLENGES At this point – while acknowledging that seal-less pumps have essentially cured the chemical-leak conundrum – let’s delve deeper into the causes and effects of the common pump paint points and highlight how centrifugal pumps and internal gear pumps have risen as the leading technologies in the ongoing battle to optimise pump performance.
Te dominant technology for seal-less pumps in chemical-transfer applications has been centrifugal pumps because their manufacturers were the first to embrace the technology and develop what came to be recognised as the preferred leak-free pump style. Te result is a class of pumps that offers leak-free performance with reasonable reliability when handling a wide range of chemical products. Te success of centrifugal pumps also brought a rash of copycat models to the market, to the extent that there are now hundreds of “me too” brands available for purchase, which translates to increased market share. Similarly, the manufacturers of internal gear pumps quickly adapted their legacy sealed and packed designs to accommodate a seal-less option. Keeping the internal pumping elements unchanged, the early seal-less gear pumps provided a basic leak- free technology that was attractive during the early development of seal-less pumps.
Despite their undoubted success in penetrating the seal-less market in chemical-processing applications, centrifugal and gear pumps have inherent design and operational attributes that create challenges for the user. Tese users should be aware of these characteristics when designing systems and selecting pump technologies. In short, chemical- transfer applications are rarely pristine and can be very unpredictable, often leading to pervasive system outages and equipment failures if the proper pumping solution is not deployed. Specifically, we have the aforementioned common pain points in pump operation. Here’s a closer look at each and how centrifugal or gear pumps (or both) can fall short in satisfying these pump conditions. Dry run is defined as “operating a pump without any liquid,” but although the definition may be simple, the consequences of doing it can be anything but. When a typical seal-less pump rotates without liquid inside, it generates heat that leads to catastrophic failure of internal components. Gear pumps struggle because the internal components are constantly in contact, making them unable to handle dry-run operation without damaging internal gears, idlers, bushings and pins. Looking at centrifugal pumps, sleeve bearings are the weakest component. Various material options exist, but each leaves the pump vulnerable to dry-run failure: Silicon carbide cracks within seconds of beginning dry-run operation and requires use of power-monitoring systems to turn the pump off in the seconds before failure. Protective coatings applied to traditional bushings provide a short cumulative wear allowance that is depleted over time, is not renewable and eventually leads to failure, though when that failure is liable to occur is impossible to know succinctly.
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