When considering centrifugal fans, the traditional market—covering industrial, commercial and utility applications—often prioritizes initial cost over performance improvements and control. One key design parameter for enhancing performance is the running clearance between the movable blades and the fan hub. While tighter clearances can increase efficiency, they also introduce challenges in manufacturing and installation. Therefore, it is essential to carefully evaluate the trade-offs between initial and operating costs before deciding to implement tighter clearances.

Reducing this gap to optimize overall performance presents obstacles related to manufacturing tolerances and installation procedures. Maintaining tight clearances requires careful attention to structural rigidity, component vibrations and issues associated with the large costs of manufacturing, shipping and field assembly. However, if reducing these challenges can offset the need to address them due to improved efficiency, then implementing tighter clearances may become a viable option.

The primary question that needs to be addressed is: How much improvement can be achieved? This paper investigates the impact of the clearance gap on the performance of dual-inlet centrifugal fans. It examines pressure rise, which refers to the increase in pressure as the air moves through the fan, flow rates and efficiency across various gap sizes to identify the optimal clearance for maximizing fan performance.