The pump industry is massive and has a rich history dating back to the 2000 BC era when the Egyptians developed a ‘Shadoof’ water machine. Today, there is a wide range of pumps categorized as Positive Displacement Pumps and Centrifugal Pumps. Since there are so many varieties under these major classes, users must have criteria to follow when choosing.
When you are looking to contact a submersible pump supplier with your order, one of the essential considerations is fluid viscosity. This characteristic is important because it affects pump behaviour and performance. It is an interesting factor because it can change under different circumstances, for instance under temperature variations.
Categories of Fluid Viscosity
Depending on its viscosity, a fluid can be Dilatant, Newtonian, Pseudoplastic or Thixotropic. A fluid is considered Dilatant if any increase in shear stress makes it more viscous. Perfect examples in this category are butter, clay, and cream. Some fluids will behave in the opposite manner, such that shear stress application makes them less viscous. Ketchup is a perfect example of this category.
Thixotropic fluids are somehow similar to pseudoplastic ones because their viscosity decreases with the increase in shear stress. Uniqueness comes from the fact that this process is time-dependent. Finally, there are Newtonian fluids that have constant viscosity regardless of applied shear stress, provided the temperature remains constant. In other words, shear stress and viscosity are directly proportional to each other. Some good examples are alcohol, gasoline, and water.
The viscosity of a fluid is an important selection parameter, but other fluid properties may affect your choice. One of them is the operating temperature, which is essential for fluids whose temperatures are above 200°F. Such elevated temperatures tend to affect packing materials, mechanical seal, pump materials, and other crucial components. Other fluid properties to keep in mind are vapor pressure, chemical composition, particle size, and specific gravity.
Pump Selection Process
Knowing the viscosity of a fluid and the general operating parameters can help you choose the right pump. Generally, positive displacement pumps are ideal for viscous fluids while centrifugal pumps work best with less viscous fluids. When selecting a pump, something called a pump curve comes up. If you are new to these devices, reading the curve can be a difficult undertaking. It could become even more confusing, considering that different versions of pumps display different curves.
For instance, the centrifugal pump curve demonstrates variable torque features while positive displacement pumps display constant torque. This information has been derived from numerous actual experiments that have tabulated friction loss figures for specific fluid viscosity, pipe size, and flow rate. Selection is also a matter of considering other system characteristics that may affect performance, such as flow rate, elevation, and piping configuration. If you can calculate and decipher the system demands, then you can use the available charts to select the best pump.
Pump selection is more than just choosing between centrifugal and positive displacement categories. The intricacies involved mean the average user can have difficulties choosing the right product. With pump curves and manufacturer guides, it is much easier to navigate through this stage. If you have challenges in the selection process, your submersible pump supplier can help.