How to Select the Right Pump for Oil Circulating Temperature Control Equipment
Selecting the correct pump for oil-based temperature control systems is essential to ensure optimal process performance, energy efficiency, and equipment longevity. Two primary pump types—centrifugal and positive displacement (PD)—differ in operating and performance characteristics. But it can be hard to determine when to use a centrifugal pump or a PD pump.
At Delta T Systems, we’ve transitioned away from offering PD pumps. Instead, we paired centrifugal pumps with variable frequency drives (VFDs) to deliver performance benefits once associated with PD systems.
Pumping Styles: Centrifugal vs. Positive Displacement
Centrifugal pumps generate flow by converting rotational energy from a motor into kinetic energy via a spinning impeller. This increase in fluid velocity creates pressure that moves the fluid through the system. Centrifugal pumps are dynamic by nature and respond to system pressure changes with corresponding changes in flow.
Positive displacement pumps, by contrast, move a fixed volume of fluid per revolution. They generate flow by trapping and physically displacing fluid through rotating or reciprocating mechanisms. PD pumps maintain nearly constant flow regardless of pressure changes but are less flexible in variable-load applications.
Flow Rate vs. Pressure
One of the main differences between the two pump styles is the flow rate at different pressures. As the curve on the right shows, a centrifugal pump will decrease flow rate as the pressure increases. This flow allows for adaptive system control when paired with a VFD, making it ideal for applications where load conditions fluctuate. In contrast, PD pumps maintain a steady flow even as pressure changes, but with added mechanical complexity and higher wear rates.
Combining a centrifugal pump with a VFD allows us to maintain consistent flow across a wide range of pressures, effectively replicating the performance benefit that PD pumps once provided, without the downsides of increased maintenance and efficiency loss over time.
Pump Efficiency
Pump efficiency is the ratio of the power that is put into running the pump compared to the amount of power that is transferred to the fluid in the form of flow and pressure.
Centrifugal pumps are designed to have the best efficiency at a designed pressure on the curve. Efficiency can decrease if operated too far from this point. Fortunately, VFD integration allows precise control over pump speed, keeping the system operating close to its BEP across different loads.
Positive displacement pumps are almost unaffected by an increase in pressure. A PD pump is most efficient with no pressure. As pressure increases, there is slightly more slip in the pump. Viscosity also plays a large part in the efficiency of a PD pump. As the fluid becomes more viscous, it gets harder for the fluid to slip between the clearances in the pump, which increases the volumetric efficiency.
Choosing the Right Pump for Oil Temperature Control
There are many factors that play a role while deciding on a pump for your application. It’s essential to select a pump for your oil TCU that balances consistency, control, and cost of ownership.
Delta T Systems uses centrifugal pumps with VFDs to provide:
- Smooth, controlled flow across varying pressures
- Efficient performance across a broad range of operating conditions
- Reduced mechanical wear and maintenance requirements
- Flexibility to adapt to multiple applications or system changes
This approach eliminates the need for PD pumps—streamlining system design, improving reliability, and enhancing process control.