(1) change of valve opening
Change the pump outlet valve, its essence is to change line characteristic curve. As shown in the following figure, when the valve is closed hours, local resistance increase pipeline, pipeline characteristics curve steepening, work by m to M1, reduce traffic from QM to QM1. When the valve is open when the pipeline resistance decreases, pipeline characteristics curve becomes flatter, work point to M2, increased traffic to the QM2.
Valves regulate the flow easy and quick, and the flow can vary continuously and suitable for continuous production of chemical characteristics. So it is widely used. Disadvantages are the valves closed hours, resistance loss, increased energy consumption, is not economic.
(2) changing the pump speed
Changing the speed of the pump is essentially changing the characteristic curve of the pump. Pumping speed of n, m, as shown in the following figure, if the pump speed is raised to the N1, the pump characteristic curve H--Q to move, work by m to M1, increased traffic from QM to QM1. If N2 pump speed, working point to M2, flow to QM2.
This method need speed or expensive variable speed motor, and difficult to achieve continuous flow, it is rarely used in chemical production.