Centrifugal fans are widely used in various industrial applications for ventilation, cooling, and material handling. Accurately measuring the static pressure generated by these fans is critical for assessing their performance and ensuring optimal system design.
This blog post provides a step-by-step guide on measuring the static pressure of centrifugal fans using pressure gauges or manometers.
Step 1: Locate the Measurement Points
To measure the static pressure of a centrifugal fan, you first need to identify the appropriate measurement points. These points are typically located at the fan’s inlet and outlet.
The inlet measurement point should be positioned at the center of the inlet duct, about two to three duct diameters upstream from the fan’s inlet. The outlet measurement point should be located at the center of the outlet duct, approximately two to three duct diameters downstream from the fan’s outlet.
It is essential to choose measurement points that are far enough away from the fan to avoid turbulence and ensure accurate readings. Turbulence can cause fluctuations in pressure measurements, leading to inaccurate results. By selecting measurement points at a sufficient distance from the fan, you can obtain more stable and reliable pressure readings.
Step 2: Install the Pressure Gauge or Manometer
Once you have identified the measurement points, the next step is to install the pressure gauge or manometer. A pressure gauge is a device that directly measures the static pressure, while a manometer measures the pressure difference between two points using a liquid column.
For a pressure gauge, drill a small hole at each measurement point just large enough to accommodate the gauge’s probe. Insert the probe into the hole, ensuring that it is perpendicular to the airflow and flush with the inside of the duct. Secure the gauge in place to prevent any air leaks around the probe.
If using a manometer, you will need to install static pressure taps at the measurement points. These taps are small tubes that protrude into the duct, with one end connected to the manometer. Drill holes at the measurement points and insert the static pressure taps, ensuring they are perpendicular to the airflow. Connect the taps to the manometer using tubing, making sure there are no leaks in the connections.
Step 3: Measure the Fan’s Inlet Static Pressure
With the pressure gauge or manometer installed, you can now measure the fan’s inlet static pressure. For a pressure gauge, simply read the value displayed on the gauge at the inlet measurement point. The static pressure will be indicated in units such as inches of water gauge (in. w.g.) or Pascals (Pa).
If using a manometer, the static pressure is determined by the difference in the liquid column’s height between the two sides of the manometer. The manometer should be level and zeroed before taking the measurement. Read the difference in the liquid column’s height and convert it to the appropriate pressure units using the conversion factor for the specific liquid used (e.g., water or mercury).
Record the inlet static pressure value for later use in calculating the total static pressure.
Step 4: Measure the Fan’s Outlet Static Pressure
Next, measure the fan’s outlet static pressure using the same method as described in Step 3. For a pressure gauge, read the value displayed on the gauge at the outlet measurement point. For a manometer, read the difference in the liquid column’s height between the two sides of the manometer.
Record the outlet static pressure value for use in calculating the total static pressure.
Step 5: Calculate the Total Static Pressure
To calculate the total static pressure of the centrifugal fan, subtract the inlet static pressure from the outlet static pressure. This difference represents the total static pressure generated by the fan.
Total Static Pressure = Outlet Static Pressure – Inlet Static Pressure
For example, if the outlet static pressure is 2.5 in. w.g. and the inlet static pressure is 0.5 in. w.g., the total static pressure would be:
Total Static Pressure = 2.5 in. w.g. – 0.5 in. w.g. = 2.0 in. w.g.
The total static pressure is an essential parameter for evaluating the performance of a centrifugal fan. It indicates the fan’s ability to overcome the resistance to airflow in the system, including ductwork, filters, and other components. A higher total static pressure generally means the fan is capable of moving air through a system with greater resistance.
