Fans used in industrial production and ventilation are basically driven by electric motors, and centrifugal fans are no exception as fans for ventilation and exhaust. The pressure of the centrifugal fan is determined. What is the relationship between the air inlet of the centrifugal fan and the current?
1) The relationship between the air inlet of the centrifugal fan and the current
In the previous article “How to realize no-load start of centrifugal fan”, I introduced to you that to achieve no-load start, it is necessary to directly close the air inlet valve, and then start the fan. The reason is that after the air inlet is closed, the extra centrifugal fan The smaller the load, the smaller the pressure. For the only impeller load, the rated current of the motor can easily drive it all. Therefore, the relationship between the air inlet of the centrifugal fan and the current is actually:
1. When the fan starts, the larger the air inlet, the greater the wind pressure, the faster the motor rotates, and the higher the current;
2. When the fan starts, the smaller the air inlet, the smaller the wind pressure, the slower the motor rotates, and the lower the current.
In fact, the current status of the centrifugal fan is not only related to the adjustment of the air inlet, but also the load of the fan and the rated power of the motor will directly affect the size of the current, but because most centrifugal fans are designed with a certain amount of motor margin, so Appropriately high loads will not cause overcurrent conditions, but since the impeller does not have a driven inertia during startup, the required motor power is already large. At this time, the complete opening of the air inlet will exceed the pressure due to too much. load, causing excessive motor current.
2)the adjustment method of the air inlet of the centrifugal fan
1. Adjustment at startup: The valve at the air inlet of the centrifugal fan is mainly used to adjust the air pressure and air volume of the fan. The air inlet valve can avoid the overcurrent fault of the motor, and gradually open the air door after the fan is fully started.
2. Adjustment during operation: When the centrifugal fan is running, it needs a certain wind pressure to discharge the gas, and the main method of controlling the wind pressure is not on the air inlet valve, but on the impeller. In terms of specific form and motor power, when larger air volume and air pressure are required, in order to ensure the efficiency of the fan, it is necessary to open the air inlet valve larger.
3. Adjustment during shutdown: When the centrifugal fan is stopped, the air inlet valve should be kept open, because the impeller of the fan does not stop rotating directly, but has a braking process, and the impeller still remains at this time. During rotation, if the air inlet valve is closed, all the air in the fan will be thrown out by the impeller, so that a state similar to vacuum appears in the volute, which will cause the volute to undergo a large atmospheric pressure and cause concave deformation. Therefore, the impeller should be completely Stop and then close the air inlet valve.