Definition of Centrifugal/Rotodynamic and Positive Displacement Pumps

Depending on the type of pump, these have different parts that allow the pressure of the fluid to be pumped to be raised. Therefore, in this section we will see the main types of pumps and their characteristics. The classification The most general of pumps is whether they are rotodynamic or positive displacement. Within the first group are the centrifugal and peripheral pumps, while in the second group we have the reciprocating and rotary pumps.

Centrifugal pumps

Many authors propose sub-classifications within the different groups, for example, within centrifugal pumps can be referred to as diffuser type, turbine type, if we classify them according to their design; while, if we classify them according to the flow direction, they can be radial, axial or mixed. In general, these types of pumps are used to drive fluids in chemical processes,

food, since the internal components can be made of materials such as stainless steel, cooling systems and other services.

Centrifugal pumps, as their name indicates, can have different shapes, but all of them are hydraulic pumps that are driven under the work of a force centrifugal These pumps work with an impeller that is rotating inside a box, the blades or vanes of the impeller transmit Kinetic energy to the fluid and raise its pressure. In the suction, the axis is coincident with the axis of rotation of the impeller while the discharge occurs in the same plane, but in the axis normal to the suction. Another constituent element of this type of pump is the volute box, which gradually increases its section until discharge and then, the Energy kinetic energy is converted into pressure energy.

Due to the typical problems of these pumps, the sealing of the shaft is a fundamental element. In general, we commonly see two types of sealing, the packing seal or the mechanical seal. However, they have other advantages, since they are compact, their maintenance It is reduced and they have a great versatility in the processes. In addition, the coupling mechanisms are simple and, in general, do not require regulators.

positive displacement pumps

While a centrifugal pump has a head curve developed as a function of the working flow rate, it is In other words, a higher flow rate drives at a lower height, positive displacement pumps work with a flow rate constant. This represents the greatest advantage of this type of pump, since it is practically independent of the elevation height, being good pumps for injection or dosage. This type of pump is widely used in boilers, where we must ensure a constant flow to avoid accidents and also work at high pressures. In addition, in matters of hygiene they are more beneficial, which is why they are also widely used in processes in the food and pharmaceutical industries.

In matters of disadvantages, it can be mentioned that they are more expensive and having a greater number of pieces, their maintenance is more expensive and complex as well as there are more parts subjected to wear.

In constructive matters there are different types of positive displacement pumps, for example, oscillating and rotary. All of them work from the same principle, when in the main body the work space that contains the fluid is reduced, this is driven and discharged, while, when the working section is increased again, it makes room for the suction to start another cycle of impulsion. Since the flow rate is practically independent of the height developed, the limiting pressure turns out to be a check valve. security. In order to regulate the flow, the number of revolutions must be modified and thus obtain different operating points.

When selecting one or another pump, the characteristics of the fluid that we want to drive must be taken into account, for example, if it is viscous, if it is at a temperature high, if it is a liquid-gas mixture, if it has solids, if it is from wastewater treatment, as well as we must think in what process and under what conditions should it act.

Topics in Centrifugal/Rotodynamic and Positive Displacement Pumps