Wallace Wittkoff is the Hygienic Director for Dover Corporation
Eccentric Disc Design Pump Components
The actual pumping mechanism is similar to the peristaltic effect of hose pumps, but this pump does not use hoses, so it does not fall victim to any of the possible issues associated with them. The disc of the pump is driven by the eccentric movement of the shaft, which produces a peristaltic effect on a channeled cylinder. Product flows in an inner and outer pumping chamber, producing fully complementary flows. The pump, therefore, does not produce pulsation. Since this pump does not depend on clearances for operation and, in fact, takes up clearance that could be generated by wear, the pump has negligible slip. The result of this was illustrated in the “Efficiency Matters” columns published in Pumps & Systems April and May 2010. With no mechanical seal, there are no surfaces on which products, such as corn syrup, liquid sugar, glucose or any number of difficult-to-seal fluids can crystallize. Therefore, the need for flush water to remove these products is eliminated.
Why Discard What You Already Pumped?
The eccentric movement pump concept goes beyond resolving global efficiency issues from a water or seal-flush use perspective. During the production cycle of a traditional pumping system, startup and shutdown are highly inefficient because:
- The pumping system is not stabilized, so the product being pumped is not to specification and must be re-worked or treated.
- For most pumps, once the inlet tank is empty and the pump loses prime, the discharge line remains full of product and also becomes a loss.
It is clear that pumping a product and then not using it is an inefficient use of resources. Disposing or treating this unsuitable fluid further adds to this inefficiency.
Efficiencies when Starting a Process
Since it has essentially no slip, the eccentric movement technology is able to produce a stabilized and usable product flow much earlier in the startup process. This compares with pump styles that have slip and require a control system to adjust and compensate. As a field application example, companies that use spray-drying processes find this to be the case in their operations.
Typically, processes of this nature begin on water for calibration and stabilization. The water is replaced with actual product. However, a process upset occurs when this change occurs. The degree to which a pump has no slip and can maintain constant flow during the transition is related to how the process retains stability and product losses are minimized during transition. In the case of spray driers, much like shower heads, if flow changes the spray pattern changes, rendering differences in the product and possible rejection.
Efficiencies when Ending a Pumping Process
On termination of a process, the residual product left in the pump discharge line also represents an opportunity for added costs, as well as waste-treatment costs.
In another field application example, a company that produces coffee extract was able to recover an additional 400 pounds of product at the end of each run because, even after the feed tank was empty, the pump continued to effectively pump air, thus helping purge the line. Pumps that are able to run dry and perform this way can produce a compressor effect following the product. Pumps that employ the eccentric movement principle produce such an effect. When considering the effect of efficiency, recovering 400 pounds per run meant:
- Resources did not need to be used in treating it as waste
- All the resources to produce it were not lost
- Resources would not be used to reproduce the lost coffee extract
The additional, indirect efficiency issue was that coffee extract was aggressive on mechanical seals and required advanced seals or water flush. Eccentric movement technology, with its sealless design, also helped in this application because resources were not expended for seal water, product was not lost, and treatment to remove the lost product was not needed.
Putting It All Together
While it is important to consider the direct efficiency parameters of a pump, such as the amount of product pumped per unit energy consumed, considerations should include the indirect efficiency consequences of pump technology selection. The issues of periphery services to the pump—such as seal water, or consequences of the pump design, such as the amount of product loss and waste treatment costs—all combine to create the true efficiency of the product-transfer process.
Pumps & Systems, October 2010