Centrifugal fans are used in many fields, and there are many types. According to the design of the impeller, they are divided into two types: forward-inclined and backward-inclined fans, and their performance characteristics and usage methods are also different.
1. Characteristic curve of forward inclined centrifugal fan
The above picture is the performance curve and flow-power curve of a typical forward-inclined centrifugal fan. It can be found that the two curves of the forward inclined centrifugal fan have the following characteristics:
1. The power decreases as the flow decreases.
2. The prohibited use area of some models is in the low pressure area.
Although the forward-inclined centrifugal fan also has a prohibited working area, not every forward-inclined centrifugal fan will have a prohibited working area. The power of the forward-inclined centrifugal fan decreases with the decrease of the flow rate, which means that when the static pressure is 0, the power of the fan will become very large, and correspondingly, the temperature rise of the motor will be very high. In order to make the forward-inclined centrifugal fan work normally under certain temperature conditions, the upper limit of its temperature rise must be limited to prevent the motor from overheating. Therefore, for some high-power fans, a lower limit of allowable static pressure must be set, and when the static pressure is less than this lower limit of allowable static pressure, the fan enters the forbidden working area.
2. Precautions for the use of forward inclined centrifugal fans
Due to the unique characteristics of high pressure and low power, the forward inclined centrifugal fan should pay attention to the following matters when using it:
1. Do not use in open spaces
Due to the low static pressure in the open space, running the forward-inclined centrifugal fan with power on in this environment is very likely to cause the motor to overheat and burn out quickly. Therefore, in the occasions where power-on operation/trial operation is required, such as on-site inspection, be sure to avoid the forward-inclined centrifugal fan in an open space. If the test site is relatively open, a wind deflector can be placed near the air inlet to artificially increase the static pressure to avoid overheating of the motor.
2. The volute installation avoids “pulling up and down”
The volute of the forward-inclined centrifugal fan is often equipped with accessories such as foot flanges, air outlet flanges, etc., which are convenient for customers to install. However, when installing, in order to ensure the life of the volute, customers should pay attention to all the flange interfaces, there can only be one hard connection made of hard materials, and the other flange interfaces are either not used or soft connections are used. If the volute has multiple hard connections, it will have the effect of “pulling up and pulling down” on the volute, and the energy generated by the vibration of the fan during daily use cannot be effectively released, which will cause serious damage or even tearing of the volute in the long run. Therefore, it should be noted that there can only be one hard link.