Field Adjustment of Impeller‑Volute Clearance for GH 150 High‑Head Gravel Pump: Comparison of Shim Method and Grinding Method

Introduction

The GH 150 is a high‑head GH series gravel pump (150mm discharge), with single‑stage head up to 60‑80 meters. It is widely used in river sand mining, reclamation, and long‑distance gravel transport – applications involving large particles and high abrasion. The radial clearance between the impeller and volute is a critical parameter affecting pump efficiency and particle passage capability. Excessive clearance increases internal leakage and reduces efficiency; insufficient clearance causes coarse particles (cobbles, gravel) to jam between the impeller and volute, leading to impeller seizure, motor overload, and even pump casing damage.

When clearance exceeds the allowable limit during field repair, two adjustment methods are commonly used: the shim method (adjusting the impeller‘s axial position to change radial clearance) and the grinding method (directly grinding the volute inner wall or impeller outer diameter). Each method has its own applicability, operation points, and risks. Based on extensive field practice, Hebei Xingou Machinery Equipment Co., Ltd. compares the characteristics, accuracy, risks, and procedures of these two methods, helping users choose the most suitable adjustment approach for their specific conditions.

1. Criteria for Excessive Clearance

For a new GH 150 gravel pump, the factory radial clearance is typically 0.5‑0.7 mm. As operating hours accumulate, the impeller outer diameter and volute inner wall wear due to slurry erosion, causing clearance to increase gradually.

Measurement method: Stop the pump, remove the cover, and use a feeler gauge to measure the radial clearance at 3‑4 points around the impeller circumference. Average the readings. Also measure the impeller OD and volute ID to verify the calculated clearance.

2. Adjustment Method 1: Shim Method

2.1 Principle

The shim method involves adding or removing shims at the joint between the bearing housing and the bracket, thereby changing the impeller‘s axial position. Because the volute flow passage is involute‑shaped, axial movement of the impeller changes the radial clearance at the discharge. Moving the impeller toward the pump inlet (adding shims) reduces radial clearance; moving it toward the motor (removing shims) increases radial clearance.

2.2 Procedure

2.3 Advantages and Limitations

3. Adjustment Method 2: Grinding Method

3.1 Principle

The grinding method directly removes material from the volute inner wall or impeller outer diameter to change the fit size, thereby adjusting radial clearance. When clearance is too large (need to reduce it), the volute inner wall is ground. When clearance is too small or there are localized high spots on the impeller, the impeller outer diameter is ground.

3.2 Procedure

3.3 Advantages and Limitations

4. Comparison of the Two Methods

5. Case Study: GH 150 Clearance Adjustment at a Sand Mining Site

Background: A GH 150 gravel pump had operated for about 3,000 hours. Efficiency had noticeably decreased, and discharge pressure was low. Measurement showed that the impeller‑volute radial clearance had increased from the initial 0.6 mm to 1.4 mm.

Adjustment: The shim method was chosen as the first option. A 0.8 mm stainless steel shim was added between the bearing housing and bracket, moving the impeller toward the pump inlet. After reassembly, the clearance was measured at 0.65 mm.

Results:

• Pump efficiency recovered to 96% of the new pump level.

• Discharge pressure returned to normal, and flow met requirements.

• After 1,000 hours of operation, the clearance showed no significant change.

Alternative experience: On another pump, the volute inner wall had localized severe wear (irregular pits). After shim adjustment, the clearance remained uneven (1.2 mm at max, 0.7 mm at min). The volute inner wall was uniformly ground to eliminate irregularities, achieving a final clearance of 0.7‑0.8 mm, with good results.

6. Selection Decision Guide

Conclusion

For adjusting the impeller‑volute radial clearance of a GH 150 high‑head gravel pump, the shim method is the preferred choice. It is non‑destructive, precise, and reversible, effectively restoring pump efficiency and extending wear part life. When clearance is uneven, localized wear is severe, or the pump cannot be disassembled, the grinding method serves as a complementary approach to quickly resolve the issue. Regardless of the method used, always re‑measure the clearance after adjustment and perform static balancing (if the impeller was ground). Hebei Xingou Machinery Equipment Co., Ltd. offers on‑site clearance measurement and adjustment services. Please contact us.