The diesel cast iron pump is the inherent characteristic of the pump itself, it has nothing to do with the external use. However, once the pump is arranged to work in a certain pipeline system, its actual working situation is not only related to the characteristics of the centrifugal pump itself, but also depends on the working characteristics of the pipeline. Therefore, to select and use the centrifugal pump well, the characteristics of the pipeline must also be considered.
When conveying liquid in a specific pipeline, the required pressure head He of the pipeline changes with the square of the flow rate Qe. Drawing this relationship on the graph paper is the corresponding pipeline characteristic curve.
If the characteristic curve of the centrifugal pump and the characteristic curve of the pipeline are drawn on the same graph paper, the intersection point M of the two lines is called the working point of the pump. When selecting the pump, it is required that the flow and pressure head corresponding to the working point can not only meet the requirements of the piping system, but also happen to be provided by the centrifugal pump, namely Q=Qe, H=He.
The flow rate of the cast iron pump needs to be adjusted in the following ways:
(1) Change the opening of the valve
Changing the valve switch on the outlet pipeline of the centrifugal pump is essentially changing the pipeline characteristic curve. As shown in the figure below, when the valve is closed small, the local resistance of the pipeline increases, the pipeline characteristic curve becomes steep, the operating point moves from M to M1, and the flow rate decreases from QM to QM1. When the valve is opened larger, the pipeline resistance decreases, the pipeline characteristic curve becomes flatter, the operating point moves to M2, and the flow rate increases to QM2.
It is quick and convenient to use the valve to adjust the flow, and the flow can be changed continuously, which is suitable for the characteristics of continuous chemical production. So the application is very wide. The disadvantage is that when the valve is closed for hours, the resistance loss will increase, and the energy consumption will increase, which is very uneconomical.
(2) Change the speed of the pump
Changing the speed of the pump is essentially changing the characteristic curve of the pump. The original speed of the pump is n and the working point is M. As shown in the figure below, if the speed of the pump is increased to n1, the characteristic curve of the pump H——Q will move up, the working point will be moved from M to M1, and the flow will increase from QM. To QM1. If the pump speed is reduced to n2, the working point is moved to M2, and the flow rate is reduced to QM2.
This adjustment method requires a variable speed device or an expensive variable speed prime mover, and it is difficult to continuously adjust the flow rate, so it is rarely used in chemical production.