What are the two most commonly used adjustment methods of horizontal multistage centrifugal pump. The simplest way to change the flow rate of centrifugal pump by valve throttling is to adjust the opening of outlet valve of pump, while the speed of horizontal multi-stage centrifugal pump remains unchanged (generally rated speed), its essence is to change the position of pipeline characteristic curve.
The simplest way to change the flow rate of centrifugal pump is to adjust the opening of pump outlet valve, while the speed of horizontal multi-stage centrifugal pump remains unchanged (generally rated speed), its essence is to change the position of pipeline characteristic curve to change the operating point of pump. The intersection point of pump characteristic curve Q-H and pipeline characteristic curve Q - ∑ h is the limit operating point of the pump when the valve is fully open. When the valve is turned down, the local resistance of the pipeline increases, the pump operating point moves to the left, and the corresponding flow decreases. When the valve is fully closed, the resistance is infinite and the flow is zero. At this time, the pipeline characteristic curve coincides with the ordinate. It can be seen that when the flow is controlled by closing the valve, the water supply capacity and head characteristics of the multi-stage centrifugal pump remain unchanged, and the pipe resistance characteristics will change with the change of valve opening. This method is easy to operate, continuous flow, can be adjusted between a certain maximum flow and zero, and no additional investment is needed. But throttling regulation is to consume the excess energy of centrifugal pump to maintain a certain supply, and the efficiency of centrifugal pump will also decline, which is not reasonable economically.
The deviation of operating point from high efficiency zone is the basic condition for pump speed regulation. When the speed of multi-stage centrifugal pump changes, the valve opening remains unchanged (usually the maximum opening), the pipeline system characteristics remain unchanged, and the water supply capacity and head characteristics change accordingly. When the required flow is less than the rated flow, the head of variable frequency speed regulation is smaller than that of valve throttling, so the water supply power required by frequency conversion speed regulation is also smaller than that of valve throttling. Obviously, compared with valve throttling, the energy-saving effect of frequency conversion speed regulation is very prominent, and the working efficiency of horizontal multistage centrifugal pump is higher. In addition, the adoption of variable frequency speed regulation can not only reduce the possibility of cavitation of centrifugal pump, but also prolong the start-up / shutdown process by preset the time of speed up / down, which greatly reduces the dynamic torque, thus eliminating the destructive water hammer effect to a great extent, and greatly prolonging the life of the pump and pipeline system.
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