Choosing The Right Pump: Why It’s Never One-Size-Fits-All
Selecting the right pump can be an overwhelming task, especially with so many technologies, variables and performance considerations to weigh up. Pipes, Pumps & Valves Africa unpacks the complexities of pump selection and explores what truly drives the right choice for each application.
Identifying the best pump for a specific application is far from straightforward. “We would all love a pump that can do it all – the Swiss pocket knife of pumping,” said Robert Kurz, director sales and marketing/vice president at NETZSCH Pumps & Systems. “But the world of pumps doesn’t work like that.” The German family-owned manufacturer specialises in rotating displacement technologies and offers progressing cavity, lobe, multi-screw and peristaltic pumps along with drive systems, accessories and IoT solutions.
With five production sites, eight assembly plants and more than 200 distributors worldwide, their global footprint mirrors the diversity of applications pumps must serve. Speaking during a recent online presentation, Kurz, however, emphasised one core message: pump selection begins with understanding your media and operating environment long before any model or technology is chosen.
Know your medium first
Pumps are used in an astonishing range of industries - from wastewater and sludge handling to petrochemical plants, food processing and multiphase crude oil applications. That diversity means operators must first answer a long checklist of questions about their conveyed media.
“What does the medium look like? What is its chemical composition, density, viscosity, temperature range, vapour pressure, particle size, corrosiveness or toxicity?” asked Kurz. Each of these influences the pump type, materials and sealing systems. It may even determine whether a hermetically sealed pump is required.
Viscosity alone can completely change pump behaviour. Waterlike fluids behave entirely differently from sticky honey, abrasive slurries or multiphase crude oil containing sand, water and gas. Food products can range from milk to thick pastes. Sewage sludge may carry high solids content. Each requires a distinct pumping approach.
Understand your operating parameters
“Once the medium is understood, the second step is defining the installation and performance requirements,” said Kurz. “Key considerations include flow rate (fixed or variable), pressure/head, self-priming capability, NPSH conditions, drive type, available infrastructure (electric, air, hydraulic), and whether the operating mode is continuous or intermittent. Spatial constraints also matter: some sites are greenfield with ample room, while others are tight retrofits. Together, these form the boundary conditions that determine which pump families can be considered and which cannot.”
The pump landscape: Centrifugal vs positive displacement
Kurz outlined the main pump categories used in industry: centrifugal (kinetic) pumps, which include rotary types with open or closed impellers and multistage designs, and positive displacement (PD) pumps, which include reciprocating piston and diaphragm pumps as well as rotary PD options such as screw, peristaltic, gear, impeller vane and progressing cavity pumps.
“It’s really not easy to find the right pump for a certain application,” he said, noting how differently these technologies behave in terms of efficiency, pulsation, solids handling and pressure capability.
One of his key selection tools is the link between specific speed and efficiency. High specific speeds favour centrifugal pumps, low values favour PD pumps, and a transition zone exists where either may work depending on the duty. QH diagrams, plotting flow against head, help determine which technologies can meet required capacities: centrifugal pumps dominate very high flow rates up to roughly 100 000 m³/h; reciprocating PD pumps reach extreme pressures of around 1 000 bar; and rotary PD pumps excel in low-flow or highly viscous applications where centrifugals become inefficient.
Centrifugal pumps remain the most widely used due to their robustness, simplicity and near-pulsation-free flow and they are available in many materials and sealing arrangements. Their limitations include non-self-priming behaviour, sensitivity to gas, higher NPSH requirements and poor suitability for viscous or very low-flow applications. As viscosity rises, flow and head decrease while energy consumption increases, often making PD pumps the better choice.
Among oscillating PD pumps, diaphragm pumps offer self-priming, dry-run capability and stable flow independent of pressure but suffer from high pulsation, limited capacity and sensitivity to solids or viscous fluids.
Piston pumps handle very high pressures, viscous media and solids but also generate strong pulsation, have limited flow rates and involve many moving parts with higher maintenance needs. Rotary PD pumps each have distinct characteristics. Gear pumps are compact and handle high pressures and viscous fluids but do not tolerate dry running and are sensitive to abrasive solids. Lobe pumps offer reversible flow, self-priming and CIP/SIP capability but require precise rotor positioning, use two shaft seals and face temperature limits in rubber-lined builds. Multi-screw pumps are versatile across chemicals, food and oil and gas multiphase duties with strong self-priming performance, though they are sensitive to solids and can be vulnerable to cavitation or aeration.
Peristaltic pumps, valued for dry-run tolerance, solids handling and reversible flow with no shaft seal, have limited flow and pressure ranges and higher hose wear.
Progressing cavity pumps provide low-NPSH, self-priming performance for viscous and high-solids media with relatively low pulsation, but require more installation space and face temperature constraints due to elastomer stators.
Safety, selection tools and the bigger picture
Kurz emphasised that safety remains critical - particularly with positive displacement pumps, where pressure is unlimited and can rise uncontrollably if a discharge valve is closed.
As a rule, every PD installation must include overpressure protection, whether through sensors that shut off the motor or a bypass system. Treating a PD pump like a centrifugal and throttling against a closed valve, he warned, is a common cause of failure.
To simplify decision-making, NETZSCH uses a digital selection tool that weighs application parameters such as flow, pressure, viscosity, temperature and space constraints, then ranks suitable pump technologies. This helps operators compare realistic options and choose the best fit. Kurz closed by noting that pump selection is never just about flow and head. Factors such as viscosity, sealing, self-priming capability, installation layout and temperature conditions all play a role. “Understanding these factors is the key to choosing the right pump,” he said.
NETZSCH Pumps & Systems,
+27 (0) 11 794 8975,
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