Issues regarding the inlet butterfly valve of the centrifugal main fan

Export regulation isn’t effective; flow rate must be controlled through the inlet

1. As far as I know, main fans generally use multi-stage, axial-flow, or centrifugal fans. These fans are characterized by high flow rates, but low outlet pressure. The stationary blades of axial-flow fans can usually be adjusted in angle, and modern axial-flow fans are equipped with a hydraulic adjustment system for these stationary blades. When the fan is in operation, the installation angle between the stationary blades and the rotating blades can be adjusted via the static blade hydraulic control device, and maintained at a certain angle to ensure high efficiency even under varying operating conditions. The flow rate of the axial flow fan is regulated by the inlet butterfly valve. 2. Centrifugal compressors generally also use multi-stage centrifugal impellers. Due to their high outlet pressure, flow rate is usually controlled by an outlet valve and a return valve; if a inlet butterfly valve is used to control the flow rate, noise and resonance can occur when the flow rate is too low.

This issue becomes easy to understand if you know how to operate it correctly: before starting the centrifugal fan, the inlet butterfly valve must be closed while the outlet valve is opened. Only after the fan is running properly and the current is stable can the inlet valve be adjusted; at this point, it’s also important to ensure that the current remains below the rated value. The advantage of doing this is to protect the motor.

The inlet valve is closed, so is the inlet vent valve closed or open? Won’t it still generate significant negative pressure even when it’s turned on?

I’m not very familiar with the main fan either; what is the purpose of the inlet vent valve? ? Isn’t it usually the outlet vent valve that is used? On our side, it’s the inlet for the Qifeng mechanism, with an outlet for venting.

In fact, most compressors these days also regulate the load by adjusting the inlet.

In that case, if it’s not controlled properly, wouldn’t it be easy to cause surge? ? ?

All have anti-surge systems; air compressors generally use venting along with opening the inlet guide vanes to prevent surge, while harmful or valuable gases usually have return pipelines in place. As for fans with lower pressure levels or inadequate supporting facilities at low costs, it is still up to the operator to figure out the ranges of pressure and current on their own, in order to try to avoid surge phenomena.

Centrifugal compressors use check valves for control

Most centrifugal compressors are also controlled at the inlet, using inlet guide vanes and inlet valves. There are also those with outlet vane control or speed control. Look at user needs