I. Required Tools:
Diesel fuel, a wire brush, feeler gauges (250 mm), a pull‑out claw (can be homemade), hammers (both large and small), a copper rod, chrome‑plated spray paint, and a tool for grinding the impeller (an electric grinder).
Adjustment principle:
II. A structure for adjusting the clearance between the impeller end face and the end cover of a Roots blower, characterized by the provision of a wave spring between the outer race of the bearing and the end cover, with the wave spring in a compressed state; the impeller shaft is connected to the bearing in a mating relationship; and the end of the end cover is equipped with a set nut, which presses against the outer end face of the bearing’s outer race, such that, when the set nut is tightened or loosened, the bearing, under the elastic force of the wave spring, drives the impeller shaft to move axially, thereby adjusting the clearance between the impeller end face and the end cover.
How to adjust the clearance of a Roots blower:
1. The clearance between impellers is determined using feeler gauges.
2. The impeller and the housing are ensured to fit properly through machining.
3. Adjust the shims to set the impeller axial clearance, and verify the clearance.
Reference Data (Search Notes):
The clearance between impellers is 0.4–0.5 mm; the radial clearance between the impeller and the casing is 0.2–0.3 mm; and the axial clearance between the impeller and the left and right end plates is 0.3–0.4 mm (with the left‑end‑plate clearance at least 0.05 mm greater than that of the right end plate). The meshing clearance of the synchronizing gears is 0.08–0.16 mm. Adjusting the operating clearances is the most critical—and also the most challenging—step in the entire overhaul of a Roots blower. A thorough study of the blower’s structural principles reveals that, during one complete rotation of the impellers, the clearance between the two impellers reaches its minimum at approximately ±45° relative to the horizontal axis. At these positions—two at +45° and two at −45°—the maximum axial cross‑sections of the two impellers are nearly parallel. When adjusting and measuring these clearances, this alignment can be used to confirm whether the impellers are indeed at the ±45° positions. During normal operation, wear gradually alters the clearances at the ±45° positions: the clearance at +45° tends to decrease, while that at −45° tends to increase. Once wear progresses to a certain extent—typically after 7–8 years of continuous service under proper maintenance—the impellers will inevitably come into contact, with the first point of impact occurring at the +45° position. Therefore, when setting the operating clearances, it is advisable to initially set the +45° clearance slightly larger—generally twice the value of the −45° clearance. For example, if the −45° clearance is a, then the +45° clearance should be set to 2a. Alternatively, the −45° clearance may be adjusted directly to 0.4–0.5 mm or even smaller; note, however, that a larger −45° clearance will reduce the air flow rate. After adjustment, reposition the locating pins offset from their original locations. The clearance between the impeller and the left/right end plates can be fine‑tuned by adding or removing shims at the bearing end covers. By contrast, the clearance between the impeller and the casing, as well as the meshing clearance of the synchronizing gears, are fixed and cannot be adjusted. During maintenance, meticulous measurement records must be kept, documenting pre‑repair, post‑repair, and newly replaced component data.
