Daily Question: Methanol Technology Exchange Edition 20080311
Thread Content
Learn from the advanced practices of the *Brothers section; there are rewards for correct answers – any answer earns a reward, allowing us to grow and mature through these Q&A sessions. Short answer: Why is the outlet valve closed when starting a centrifugal pump, and why cannot it remain closed for too long?
Close the outlet valve when starting the centrifugal pump; at startup the motor load is close to no-load, making it easier to start and preventing current overload. Because when a centrifugal pump operates with its outlet valve closed for an extended period of time, the continuous rotation of the impeller causes the liquid inside the pump to be stirred and rubbed, generating high heat that can lead to deformation or damage of the components.
Close the outlet valve to temporarily reduce the outlet flow to zero; this results in the lowest power requirement for the pump, thereby keeping the motor load at its minimum level and preventing the motor from being damaged due to excessive starting currents. Once the motor is running properly, the outlet valve should be gradually opened, otherwise it will cause the pump casing to heat up and lead to damage to its components.
Close the outlet valve to temporarily reduce the outlet flow to zero; this results in the lowest power requirement for the pump, thereby keeping the motor load at its minimum level and preventing the motor from being damaged due to excessive starting currents. Once the motor is running properly, the outlet valve should be gradually opened, otherwise it will cause the pump casing to heat up and lead to damage to its components.
Close the outlet valve to temporarily reduce the outlet flow to zero; this results in the lowest power requirement for the pump, thereby keeping the motor load at its minimum level and preventing the motor from being damaged due to excessive starting currents. Once the motor is running properly, the outlet valve should be gradually opened, otherwise it will cause the pump casing to heat up and lead to damage to its components.
When the outlet valve of the centrifugal pump is not closed completely, if the flow rate decreases only slightly, it will result in a reduction in the efficiency of the centrifugal pump and wasted electricity consumption; however, it has no impact on the pump itself. Once the valve is closed to a certain limited degree, it will cause the centrifugal pump to generate more noise and vibration, and its performance will become unstable. Moreover, operating a centrifugal pump with its valves closed for an extended period can cause the temperature of the liquid inside the pump to rise. When the pump operates at a low flow rate or with no flow at all while still being closed, the water in the pump chamber circulates rapidly due to the high-speed rotation of the impeller; this friction between the water and the pump components leads to a sharp increase in the pump’s temperature, as well as an increase in the outlet pressure. If the pump temperature becomes too high, it may even result in the pump bursting. The motor current also increases, and excessive current can cause the motor to burn out. Therefore, a centrifugal pump cannot operate with its outlet valve closed for an extended period of time.
Turning off the outlet valve during startup helps to prevent excessive instantaneous current at the time of startup； Within three minutes after the pump starts, the outlet valve must be opened slowly; since the impeller is continuously doing work, if it is closed for too long, it can cause damage to the flow-related components and the outlet valve
Close the outlet valve when starting the centrifugal pump; at startup the motor load is close to no-load, making it easier to start and preventing current overload. Because when a centrifugal pump operates with its outlet valve closed for an extended period of time, the continuous rotation of the impeller causes the liquid inside the pump to be stirred and rubbed, generating high heat that can lead to deformation or damage of the components.
1. Closing the outlet valve during startup helps to reduce the starting current, thereby preventing excessive instantaneous current from damaging the motor during startup； 2. Within three minutes after the pump starts, the outlet valve must be opened slowly; as the impeller continues to do work, if it remains closed for too long, it can cause damage to the flow-related components and the outlet valve
Close the outlet valve when starting the centrifugal pump; at startup the motor load is close to no-load, making it easier to start and preventing current overload. Because when a centrifugal pump operates with its outlet valve closed for an extended period of time, the continuous rotation of the impeller causes the liquid inside the pump to be stirred and rubbed, generating high heat that can lead to deformation or damage of the components.
1. It starts more easily, preventing current overload. 2. When a centrifugal pump operates with its outlet valve closed for an extended period of time, the continuous rotation of the impeller causes the liquid inside the pump to be stirred and rubbed against one another, generating high heat that can lead to deformation or damage of the components.