What should I do if the air volume of the fan box is insufficient? Troubleshoot by control, resistance and air leakage
The air volume of a fan box in an electronics factory was normal during debugging, but after three months of operation, the air volume at the end dropped significantly. The operator's first reaction was that the motor was faulty and he was ready to replace the motor. On-site inspection found that the filter pressure difference had increased from the initial resistance to the final resistance, and the air valve opening had also been adjusted smaller. There is no problem with the motor itself. The problem is that the system resistance has changed and the fan operating point has moved along the performance curve toward the direction of small air volume.
This case illustrates a common misjudgment: insufficient air volume is not necessarily an equipment failure. Before replacing the motor or increasing the speed, check one by one according to the three directions of control, resistance and air leakage, and you can often find the real cause.
Aili Industry is discussingWhen there is an operation problem with the fan box , the current operating mode, rotation speed, valve opening, filter status and measuring point location are usually required first, and then it is determined whether the problem is on the equipment side or the system side.
Repeat the same measurement conditions first
Before comparing air volume data, first confirm whether the two measurement conditions are consistent. What needs to be recorded includes: current operating mode (full speed or on duty), fan speed, valve opening, filter status, measuring point location and measuring instruments.
If the last commissioning was performed at full speed with clean filter, and now it is in duty mode or the filter is dusty, the two air volumes cannot be directly compared. Similarly, if the measuring point location is changed from the fan outlet to the remote branch, the readings will be different. Unify the measurement conditions first, and then determine whether the air volume has really dropped.
The measuring instrument itself may also have errors. The anemometer's range, calibration status, and measurement method all affect readings. If there are multiple instruments on site, it is recommended to use the same instrument for retesting or cross comparison.
Control side: first confirm the speed and signal
The control side troubleshooting starts with the rotation speed. For fixed-speed fan chassis, it is necessary to confirm whether the power supply voltage and frequency are normal and whether the three phases are balanced. Frequency conversion or DC speed regulating fan box should confirm whether the control signal is in place and whether the analog, PWM or communication signal is consistent with the set value.
When the control signal is disconnected or has poor contact, the driver may automatically slow down or stop. If the system has minimum air supply requirements, it should not shut down after disconnection, but should be maintained at a safe preset speed. During troubleshooting, the driver input signal and output speed should be measured to confirm that they correspond.
If the speed is normal but the air volume is insufficient, the problem may be on the system side, not the control side. At this time, do not increase the speed rashly, but check the resistance and air leakage first.
Resistance side: filter section and damper are the key points
Increased system resistance is a common cause of decreased air volume. After dust accumulates in the filter section, the resistance rises and the fan operating point moves to the direction of small air volume. Adjusting the air valve opening smaller will also increase local resistance. Dust accumulation inside the air duct, clogged muffler or deformed coil fins will also consume the pressure provided by the fan.
During the inspection, record the static pressure at the fan box outlet, before and after the filter section, key elbows and the farthest end. Comparing which section the abnormal pressure loss is concentrated is more reliable than directly replacing a larger fan. If the pressure difference in the filter section is close to the final resistance, the filter should be replaced first, and then the air volume should be measured again.
System end configurationWhen using HEPA/ULPA high-efficiency filters , the initial resistance of the filter and the resistance at the end of use should be included in the calculation of the working point. If you select based on cleaning status only, the air volume may be insufficient after running for a period of time. When the process requirements are higher, it can be evaluatedDoes the ULPA ultra-high efficiency filter meet the requirements?
Clean room ceiling air supply is comparableFFU fan filter unit ; centralized management of multiple devices can be matchedThe FFU computer group control system realizes zone speed regulation and status monitoring. Protection of single process equipment can be consideredEquipment-side fan filter unit (EFU) . The final filtered air supply at the end of the air duct can beHigh-efficiency air supply outlet (HEPA BOX) . The resistance characteristics of these devices and the fan box are different and should be confirmed separately during troubleshooting.
Leakage side: fan outlet and end readings may be different
If the air volume at the fan outlet is normal but the air volume at the far end is insufficient, check the pipeline for air leakage or branch balance first. Air duct flanges, soft connections, valve shaft seals and branch pipe interfaces are all common air leakage points. Air leakage will cause the fan to supply more air, but not enough air volume at the end.
The troubleshooting method is relatively simple: use an anemometer or smoke generator to check suspected air leakage points while the fan is running. If the air leakage is serious, repair the air duct first and then measure the air volume again. Soft connections can also crack or come apart if they are stretched or squeezed.
Branch balancing problems are equally common. If multiple branches share a fan box and the valve opening of one branch is too large, the air volume of other branches will be insufficient. At this time, the branch valves should be rebalanced instead of increasing the fan speed.
Two readings point to different causes
If the air volume at the fan outlet is normal but the air volume at the far end is insufficient, check the pipeline for air leakage or branch balance first. If the air volume at the fan outlet also drops, check the rotation speed, air inlet obstruction and overall pressure loss of the system first. Failure of the fan box body cannot be determined solely by the wind speed at the end.
Blocking the air inlet is also a reason that is easily overlooked. If the air inlet of the fan box is blocked by debris, packaging or adjacent equipment, the air inlet resistance will increase and the air volume will naturally decrease. Check whether there is enough space around the air inlet and whether the filter is blocked.
Do not increase the speed first
Hastily increasing the speed may increase noise and power consumption, and may also cover up blockage or air leakage problems. After the speed is increased, the air volume may temporarily recover, but the system resistance still exists, the motor load increases, and long-term operation may be overloaded. If the filter is already close to its final resistance, increasing the speed will only make the motor work harder.
The correct sequence is: first reproduce the measurement conditions, then check the control side, then check the resistance side, and finally check the leakage side. Record data at each step to help determine which section the problem lies in.
What data should be included in the walkthrough record?
A record that can be used for troubleshooting should at least include: operating mode, speed or frequency, control signal value, fan outlet static pressure, pressure difference before and after the filter section, key valve opening, fan outlet air volume, remote air volume, motor input power and filter status.
Ai Li industrialFan box inspection and communication are based on the existing air volume, pressure, power and control status. Specific structure and configuration options can be found inIt is confirmed in the fan box product catalog that non-standard projects should provide equipment or machine room drawings, and then finalize them based on the determined working points and on-site interfaces.
