Why is the impeller of multistage pump different in size?
If the diameter of the impeller at all levels to the same size, is also possible, but requires a level after the impeller speed is higher than the previous level, it is not a plurality of impeller coaxial, the parallel connection of the equipment volume increases, and the higher the speed of the rotor part (impeller, shaft, bearing manufacturing) higher demands, increase the relative cost.
However, the rotation of the impeller speed actually is limited, it is added to the velocity of the fluid is limited, some require high speed fluid, this speed obviously can not meet the job requirements, so only to further accelerate fluid. However, after a accelerated flow, the velocity has been very fast. If the next step is accelerated or the impeller of the same size is used, then the centrifugal force remains the same at the same speed. Then one principle of centrifugal force is needed: the size of the centrifugal force is proportional to its diameter. In this way, the two stage impeller required greater diameter, in order to further accelerate the flow. At such a level of acceleration, until the proper speed is reached.
The multi-stage pump belongs to centrifugal pump, impeller centrifugal pumps are centrifugal impeller, centrifugal impeller is accelerated by centrifugal force to the fluid rotation, acceleration of the process is the process of gas or liquid increase lift boost. The surface of the rotating impeller is a curved surface that conforms to the principles of fluid mechanics. When the impeller rotates along the axis of the rotation direction of the impeller fluid enters, and blade surface contact along the curve of the surface flow, then the effect of the centrifugal force of the impeller is from the direction of impeller radius fast was thrown, thus speeding up. In theory, the faster the impeller rotates, the greater the centrifugal force, and the faster the fluid is added.
