THE RIGHT PUMP FOR THE JOB CENTRIFUGAL OR POSITIVE DISPLACEMENT? A question factory owners and engineers often ask themselves is: Do we need a positive displacement (PD) pump, or would a centrifugal model be faster? There are many processes where either design can get the job done, but when it comes to saving time and money “getting the job done” isn’t enough. Here’s a guide to pump selection that will keep your processes running smart. VISCOSITY The most important factor in determining whether to use a PD or centrifugal pump is the viscosity of the fluid you are attempting to move. Centrifugal designs struggle with thicker liquids since the unit’s impeller has to overcome more friction. Meanwhile, PD pumps’ flow rate actually increases with the viscosity of the fluid being pumped. While PD units may be lower speed than their centrifugal counterparts, when it comes to thick liquids like sewage and oils, slow and steady wins the race. CAPACITY Where centrifugal pumps win out is their ability to pump large volumes of low viscosity liquid quickly. Any fluids at 1 cSt (like water) or lower can be moved far more efficiently by one of these units than their bulkier PD counterparts. Because displacement pumps are limited to the size of their internal clearances, their capacity remains fixed. If you are moving water, light fuels, or petrochemicals, centrifugal pumps are by far the most efficient option. EXCEPTIONS TO THE RULE There are two scenarios where a PD pump may be necessary for low viscosity processes. The first is when dealing with shear-sensitive fluids — products like adhesives, paints, and gels require low-friction, steady flows in order to maintain their consistency. The second scenario is any process with a high pump head. Even in low viscosity processes, a higher pump head causes centrifugal pumps’ efficiency and flow rate to plummet. Displacement pumps are able to operate at virtually the same efficiency no matter how many feet of head are added.
• The company has time to find a suitable replacement, resulting in a smoother transition. • Remaining employees feel more comfortable when they don’t have to worry about “disappearing” overnight. Even with all these positives, Siegel notes that transparent separation may not be the best course of action for every employee termination. For example, if the soon-to-be-ex- employee is a manager whose toxic behavior is harming the work environment, they need to be shown the door immediately. Siegel claims that in two-thirds of cases, transparent separations offered the best outcome both for the company and the former employee. There are potential drawbacks to transparent separation. Opponents to this strategy note the potential damage a disgruntled employee can cause after being told they are losing their job. Some employees may even prefer to collect severance and leave so they can fully focus on the job search. Is transparent separation the answer to all your termination woes? The jury’s still out; there’s no one-size-fits-all solution to any business problem. What works great for one company might not be best for another. But if you think the pros outweigh the cons, transparent separation might be worth considering the next time your company has to say goodbye.
There are other niche situations that can affect this traditional wisdom, especially when specialized designs like vortex impellers are concerned. That’s why Pye-Barker carries such a wide selection of both centrifugal and PD pumps. No matter the needs of your process, we are prepared to meet them.
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