What should I do if the wind pressure in the fan box is too high? Check the measuring points and then check the resistance and valves

When the wind pressure is too high on site, operators often have two reactions: one is that the high pressure means the air supply is sufficient, so they don't care; the other is that when the pressure exceeds the design value, they quickly reduce the speed. Both reactions can go wrong. High pressure does not mean sufficient air volume, and high pressure does not necessarily require speed reduction. You must first figure out where the pressure is measured and why it is high.

High pressure does not necessarily mean adequate air supply

This is the easiest trap to step into. The outlet pressure of the fan is high, which may simply be because the downstream valve is closed or the filter is blocked. The airflow is held near the fan, and the pressure naturally increases, but the actual air volume passing through the system decreases. The air volume at the end is insufficient, but the pressure gauge shows a high level.

If you judge that the equipment is operating normally just by looking at the pressure reading, the farthest end may be lacking air all the time. The correct approach is to look at the air volume, pressure and valve status together. Measure the air volume at the fan outlet, measure the air volume at the critical end, and record the filter section pressure difference and valve opening at the same time. If the outlet pressure is high but the terminal air volume is low, the problem is the system resistance, not the fan.

There is another situation: the measurement is full pressure, the design document states external static pressure, and the two calibers are different. Total pressure includes dynamic pressure. When the wind speed at the fan outlet is high, dynamic pressure may account for a considerable proportion. A direct comparison between the total pressure and the external static pressure will lead to a conclusion that it is on the high side. When checking measuring points, first confirm whether the meter reads full pressure, static pressure or external static pressure.

Segmented pressure measurement to locate abnormal resistance

After confirming the pressure caliber, measure the pressure step by step along the air path. Record the static pressure at the outlet of the fan box, the front and rear of the filter section, the key elbow and the farthest end in sequence. Compare the pressure difference of each section to see which section the abnormal losses are concentrated.

If the pressure difference between the front and rear of the filter section is significantly higher than the initial resistance, it means that the filter is dusty or clogged. If the pressure difference between the front and rear of a certain valve is large, it indicates that the valve opening is improper or there is a problem with the valve core. If the pressure difference in a certain section of the air duct is abnormal, it may be due to dust accumulation inside the air duct, clogged muffler, or deformation of the coil fins.

When measuring pressure in sections, make sure that the instrument range and pressure measurement method are consistent. One section uses a large-range instrument and the other section uses a small-range instrument, and the data cannot be directly subtracted. The positions of the pressure ports should also be consistent. The full pressure is measured when facing the air flow, and the static pressure is measured when the vertical air flow is used. Mixing them will cause distortion in the comparison.

High pressure and high air volume are not the same thing

When the downstream valve is closed, the fan outlet pressure may increase, but the actual air volume through the system decreases. If high pressure is mistaken for sufficient air supply, the farthest end may continue to lack air. When handling abnormalities, record the pressure and air volume at least in pairs, and indicate the status of the air valve and filter.

There is another situation: the fan speed is high and the system resistance is normal. At this time, the pressure and air volume are both high. This is really big and needs to be slowed down. The way to distinguish is to see whether the terminal air volume exceeds the standard. If the terminal air volume does exceed the design value, it is reasonable to reduce the speed. If the air volume at the end is insufficient, high pressure is not a speed problem, but a resistance problem.

Confirm terminal requirements before making adjustments

If it is confirmed that the speed setting is too high, you can gradually reduce the speed and measure the most unfavorable end air volume at the same time. During the speed reduction process, the pressure and current must be observed simultaneously to ensure that the terminal air volume does not fall below the demand.

If the high pressure comes from valve throttling or filter blockage, the abnormal parts should be dealt with first. The valve should be opened, the filter should be replaced, and then see if the pressure returns to normal. Running the fan at higher power to overcome abnormal resistance is usually not a long-term solution. Energy consumption will increase, noise will become louder, and equipment life will be affected.

System end configurationWhen using HEPA/ULPA high-efficiency filters , the initial resistance of the filter and the resistance after use will affect the working point. If the filter is close to the final resistance and the system resistance drops after replacement, the fan operating point will move toward the direction of large air volume. At this time, the speed setting needs to be rechecked. When the process requirements are higher, it can be evaluatedDoes the ULPA ultra-high efficiency filter meet the requirements?

It is meaningful to compare with the original operating point

The baseline data left during debugging is a reference for judging whether the wind pressure is abnormal. The baseline should include: static pressure at each measuring point, filter status, valve opening, fan speed and motor input power. During subsequent maintenance, retest under the same working conditions. If the pressure difference in a certain section increases significantly, the problem can be located.

Aili Industrial has independent supporting capabilities in fans, motors, controls and sheet metal structures. The complete machine test data can be provided according to project working conditions, including external static pressure and power under specified air volume. These data can be used as a reference for on-site debugging and subsequent maintenance. The project provides actual pipeline diagrams and segmented pressure measurement results. The entire machine plan can be rechecked based on the original design instead of simply adjusting a parameter.

Recalculation is required after system resistance changes

If a branch is added to the system later, filters are replaced, or the direction of the air duct is changed, the original air box curve may no longer cover the new requirements. At this time, the pressure abnormality is not an equipment failure, but a change in system conditions. Recalculating the working point is more rational than repeatedly adjusting the valve.

Recalculation requires existing air duct diagrams, air volume, segment pressure measurement results and motor input power. Put these data on the same graph, find the new system resistance curve, and intersect it with the fan performance curve to see if the intersection falls within the usable range. If the intersection point deviates too far from the high-efficiency zone, the fan configuration may need to be adjusted or the pipeline optimized.

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 pressure characteristics of these devices and the fan box are different and should be clearly specified on the system flow diagram.

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 shape them based on the determined working points and on-site interfaces.