Introduction
Fluid mechanics can be described as the application of laws of force to the concept of motion of fluids. The mechanically produced force is used to move a fluid form through a designated routed in order to perform a certain operation. This paper focuses on the centrifugal pump as an equipment that generates the force require to move a fluid through a route in relation to the monitoring and measuring fluid behavior.
The centrifugal pump is one of the widely used equipments in hydraulic systems. They operate on the centrifugal force principle. The principle requires that a force be created by a rotating object in centrifugal motion which then creates flow by generation or addition of energy into the fluid. The pump has an inlet and an outlet. The operation of the pump is designed to increase the fluid pressure gradually. This instantaneous difference between the inlet and the outlet is what causes the motion of the fluid. This fluid motion can then be tapped as kinetic energy that is used to operate hydraulic machines and equipment (Grundfos, 2012).
The centrifugal pump produces a mechanical energy from the motor. This energy is transferred to the fluid through impellers or vanes which continuously offer a rotary movement. This rotary movement of the impeller is enabled by the rotating shaft to which the impellers are connected. As the fluid enters from the inlet, which is known as the volute to the center of the impeller, it continuously hits along the blades of the vanes and this ultimately increase the fluid velocity (Grundfos, 2012). The constant change in fluid velocity as it exits the impeller component is converted to pressure. The volute is designed to allow for expansion at different time intervals so as to produce pressure variations that are important for optimum production of pressure at the discharge point.
With the pump operating at some constant speed, there is a gradual increase in system back pressure on the stream of hydraulic fluid in the piping. This causes a reduction in the magnitude of the rate of volumetric flow which the centrifugal pump can maintain. Several factors determine the volumetric flow rate that a pump can maintain. These factors are dependent on the systems fluid and the general characteristics of the pump. System fluid variables that determine the ability of then pump to maintain the volumetric flow rate include the fluid velocity and the fluid viscosity (Grundfos, 2012). On the other hand, the diameters of the impellers and the blades, the rotational speed of the shaft, the power supply and the pump efficiency have a lot of influence on the volumetric flow rate of the pump.
These factors affect the pump head which arises from the difference between the continuously changing system back pressure and the incoming pressure for the pump. This volumetric flow rate is therefore calibrated as a function of the characteristics of the pump and the fluid and the resultant pump head value which all in general describes the rate at which the fluid flows through the pump.
Throttling involves varying one or more of the factors that affect determine the capabilities of the pump. Since fluid characteristics are hard to vary when the pump is in operation, throttling takes into account varying the output pressure along the discharge line. Otherwise, turning the pump on and off could also be used to vary the pressure. This performs the same effect as the throttle. Switching off, causes the shaft to gradually decrease its rotational speed and hence the vanes have less kinetic energy to act on the incoming flow (Tuzson, J., 2000). This means that less pressure is produced within the impeller compartment and subsequently, less pressure along the discharge line. However this option requires that the suction vessel is sizeable enough to hold a sufficient supply of the fluid as without this, the pump could easily damage due to associated suction breaks along the piping. The kickback or recirculation line is provided to ensure that in the event of blockage of the pump discharge path there is a line that can accommodate the minimum flow of the pump (Grundfos, 2012).
The shutoff pressure is one aspect of the pump that needs to be considered when designing a pump. This is the maximum amount of pressure that the pump will develop at zero-flow operation. This generally implies that the discharge line is blocked. In this case, the system must be able to offer a compromise due to the developing pressure than damaging the pump. In this case therefore, the maximum pressure of the source, maximum pump head, the maximum suction head pressure and the maximum pump operating speed determine the whole pressure designing of the pump (Bachus, L., & Custodio, A. A., 2003).
References
Bachus, L., & Custodio, A. A. (2003). Know and understand centrifugal pumps. Oxford: Elsevier.
Grundfos (2012). RESEARCH AND TECHNOLOGY: Centrifugal Pump. Retrieved from http://www.grundfos.com/content/dam/Global%20Site/Industries%20%26%20solutions/Industry/pdf/The_Centrifugal_Pump.pdf
Tuzson, J. (2000). Centrifugal pump design. New York: John Wiley & Sons.
