Fan pressure rise characteristics are normally expressed in either total pressure (TP) or static pressure (SP), with static pressure being the unit most commonly used in the United States. The fan volume flow rate (airflow) is commonly expressed in cubic feet per minute, or cfm. Therefore, the system pressure loss and volume flow rate requirements are typically expressed as a certain value of static pressure (SP) at some cfm.
The fan “pressure-volume” curve is generated by connecting the fan to a laboratory test chamber. By following very specific test procedures as outlined in the Air Movement and Control Association (AMCA) Standard 210, data points are collected and plotted graphically for a constant rpm, from a “no flow” block off condition to a “full flow” or wide condition. Figure 1 represents such a curve that is typical for a vaneaxial fan, and is commonly referred to as a “static pressure” curve.