Some questions about centrifugal pumps
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First: How does the outlet pressure change when the outlet valve is moved from fully closed to fully open in a centrifugal pump? Second: What is the effect of flow rate on the axial and radial forces acting on the rotor? Third: Why do both high flow rates and low flow rates, which deviate from the normal operating conditions, cause cavitation?
First: How does the outlet pressure of a centrifugal pump change when the outlet valve is moved from fully closed to fully open? If the system pressure is higher than the pressure at the shut-off point, there is little change as the valve moves from fully closed to fully open; over time, the pump heats up and cavitation occurs. If the system pressure does not exceed the pressure at the shut-off point, the pump does not exhibit a hump, and as the valve opening increases, the pressure decreases. If there is a hump, it rises to the hump and then drops. Second: The effect of flow rate on the axial and radial forces on the rotor. Both high and low flow rates affect the axial and radial forces; at the point of optimal efficiency, the radial force is at its minimum, resulting in minimal vibration. Changes in flow rate cause changes in pressure, and as a result, the forces acting on the inlet and outlet covers of the impeller also change; in other words, the axial force changes. Third: Why do both high flow rates and low flow rates, which deviate from the normal operating conditions, cause cavitation? When the flow rate is below the minimum value specified by the thermal control system, heat is generated inside the pump; with the inlet pressure remaining constant, the fluid vaporizes due to the high temperature, resulting in cavitation. At high flow rates, cavitation occurs due to the excessive inlet flow velocity.
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