Analysis and Solutions for Internal Flow Loss in Roots Blowers

Factors affecting the impeller clearance include: the design dimensions and tolerances of the impeller, the precision of machining and installation, and the thermal expansion and contraction caused by the temperature rise during the fan's operation. Controlling the clearance is one of the important issues to be addressed in fan design and assembly. Traditional manufacturing methods involve making the synchronous gears integral, controlling the positions and tolerances of the impeller and shaft, and the gears and shaft during assembly. Once assembled, the chasing face clearance between the two impellers cannot be adjusted, and the blade curvature must be trimmed. This trimming inevitably leads to an increase in clearance, resulting in a higher internal leakage flow rate within the fan. We now introduce an adjustable solution.

The synchronous gears are designed in a type that matches gear rings with gear hubs. During assembly, the locating pin holes for positioning the gear rings and hubs are not initially drilled. After the fan's main and driven impellers, front and rear wall panels, and the fan housing are assembled, since the positioning of the gear ring and hub of the synchronous gears has not yet been established, the gaps are adjusted to meet the design requirements. The fastening bolts connecting the gear ring and hub are then tightened, and the locating pin holes are drilled, with the locating pins inserted. This way, the assembly process includes an adjustment phase between the gear ring and hub, allowing for easier control of the internal leakage flow within the design specifications for the assembled fan.

Factors affecting the clearance between the impeller and housing include the outer diameter size of the impeller and the bored hole size of the housing, as well as the corresponding tolerance values and machining and installation precision. Since the fixed-end bearings on the main and driven shafts are mounted on the front wall plate, the clearance between the impeller and the front wall plate is relatively small; whereas the floating-end bearings on the main and driven shafts are mounted on the rear wall plate, a larger clearance should be chosen between the impeller and the rear wall plate to compensate for the thermal expansion and contraction of the main and driven shafts caused by the higher temperature rise during fan operation.