01 First, Let's Look at What Kind of Fan This Is

The fan tested this time is a high-pressure centrifugal fan, model Y6-24 NO.11D. Its design parameters are as follows:

*   Design Air Volume: 22,000 m³/h

*   Design Total Pressure: 12,000 Pa

*   Medium Temperature: 95~105℃

*   Speed: 2,950 r/min

*   Equipped Motor: 2-110kW Variable Frequency Motor

From the parameters, it is clear that this is not an ordinary fan just "blowing air," but a genuine high-pressure centrifugal fan, specifically used for the air preheater partitioned leak-proof system.

02 Why Does the Outlet Pressure "Seem Low"?

The owner's question is very reasonable: The design total pressure is 12,000 Pa, so why does the outlet pressure gauge show a value almost equal to the primary air pressure?

To answer this, we must first clarify the three basic concepts of fan pressure. The *Fan Handbook* (2nd Edition, Chapter 1, Section 6) clearly defines: *"Fan pressure is divided into three forms: static pressure, dynamic pressure, and total pressure. Among them, the pressure that overcomes the air supply resistance is static pressure, and the form that converts the kinetic energy required for gas flow into pressure is dynamic pressure."*

Simply put:

*   Static Pressure: The pressure acting vertically on the pipe wall, which is the resistance value of the pipeline system.

*   Dynamic Pressure:The pressure corresponding to the kinetic energy of the flowing gas. It requires professional instruments to measure; ordinary pressure gauges cannot detect it.

*   Total Pressure: Static pressure + Dynamic pressure. It is the true total output of the fan.

In this specific working condition, the end of the air preheater leak-proof system is connected to the primary air system, which has a positive pressure of approximately 10 kPa. **This 10 kPa is the system's resistance value and the pipeline's static pressure.**

The pressure gauge on the fan outlet pipe measures static pressure. The reading being essentially equal to the primary air pressure **is a direct reflection that the fan has overcome the system resistance and successfully pushed air into the primary air system**, indicating that the fan has successfully "withstood" the positive pressure of the primary air.

If the fan outlet pressure were lower than the primary air pressure, the air couldn't be pushed in—that would mean there is a real problem.

03 Why Look at Dynamic Pressure, Current, and Flow Rate?

1. Dynamic pressure is the "hidden contribution" invisible to pressure gauges.

Pressure gauges only measure static pressure, not dynamic pressure. Dynamic pressure requires specialized instruments like Pitot tubes or air pressure gauges to measure.

Total Pressure = Static Pressure + Dynamic Pressure. Static pressure is the part that "pushes through resistance," while dynamic pressure is the part that "makes the gas flow." The sum of the two is the true total pressure output of the fan.

2. Current is the most honest "referee" of fan output.

Data shows the motor current has reached 190A, indicating the motor is operating at full load.

For centrifugal fans, changes in flow rate are directly reflected in the current:

*   Flow rate meets standard:** The impeller does work on the gas, the motor load increases, and the current naturally rises.

*   Insufficient flow rate:** Due to excessive system resistance or improper fan selection, the gas cannot pass through normally, the impeller "spins idle," and the current will be noticeably lower.

The full-load current of 190A indicates the fan is in its rated output state, not "spinning idle" or "deadheading."

3. The flow meter is the most direct "judge."

A flow meter is installed in the system pipeline, and data shows the fan has reached the design flow rate of 22,000 m³/h.

Meeting the flow rate is the most solid evidence—it proves the fan has pushed a sufficient amount of gas into the system, so the pressure is naturally up to standard as well.

 04 What If You Absolutely Must Make the Pressure Gauge Reading Higher?

You can do this: Slightly close the manual valve in front of the air preheater.

This will artificially increase system resistance, causing the pipeline static pressure to rise, and the pressure gauge reading will naturally become higher. However, this will reduce air volume, decrease efficiency, and increase energy consumption, with no practical significance for actual operation.

Fans are designed to convey flow rate, not to "hold back pressure."As long as the flow rate is up to standard, the current is normal, and the system operates stably, the static pressure value is simply a natural reflection of the system resistance, not a signal of insufficient fan output.

In Conclusion

When a fan shows "low outlet pressure" during a test run, don't rush to suspect that the fan's pressure selection is too small or the parameters are unqualified. First, clarify these three questions:

1.  Is the pressure gauge measuring static pressure or dynamic pressure?

2.  What is the positive pressure value at the end of the system?

3.  Do the current and flow rate meet the design values?

If all three questions check out, then the displayed fan outlet pressure is normal.

Meeting the flow rate, full-load current, and stable system operation—these are far more convincing than the fluctuating numbers on a pressure gauge.