What is the new static pressure (SP) if the original SP was 1.2" and the motor sheave was changed from 2" to 2.5" in diameter?

To determine the new static pressure when changing the diameter of the motor sheave, it’s essential to understand how the size of the sheave affects the fan speed and consequently the static pressure in a system.

When the diameter of the motor sheave is increased, this will generally result in a reduction in the speed of the fan. Since fan performance curves show that static pressure drops as fan speed decreases, this change will affect the static pressure.

In this scenario, the original static pressure is 1.2". Changing the motor sheave diameter from 2" to 2.5" results in a larger sheave, which reduces the operational speed of the fan. Calculating the new static pressure involves understanding the relationship between fan speed (which changes inversely with sheave size) and static pressure.

The static pressure can be estimated using the fan laws, particularly relevant to this situation. With a larger sheave, the expected calculations (assuming the system and other variables remain constant) would yield a static pressure approximately around 1.875". This is indeed supported by the fan law calculations that show a proportional relationship between the change in diameter and the outcome in air pressure.

Thus, the new static pressure of 1.875" after changing