Submersible Pump Graphite Bushing Applications: From Clear Water to Sewage

A submersible pump integrates the motor and pump body in a single housing, widely used in deep-well water lifting, municipal sewage, agricultural drainage, mine dewatering, and offshore platform service. Because motor and pump share one body, the guide bearing must rely on the pumped medium itself (clear water, sewage, or sandy water) for lubrication. Metal or plastic bushings wear rapidly under dry or boundary lubrication, while carbon graphite bushings — thanks to self-lubricity, chemical stability, and good thermal conductivity — have become the preferred guide bearing material. Huahao Sealing Co., Ltd. supplies hundreds of thousands of graphite bushings annually to major domestic submersible pump makers; this article summarizes our selection insights.

1. Core Advantages of Graphite Bushings in Submersible Pumps

1.1 Self-Lubrication

In carbon graphite's layered crystal structure, the interlayer bond is weak, allowing easy interlayer sliding under load. This means graphite maintains a low friction coefficient (0.05~0.15) without any external lubricant. At pump startup, before the medium has reached the bearing clearance, the bushing's self-lubricity prevents dry-friction burns.

1.2 Adaptability to Water Lubrication

Water as a lubricant has very low viscosity, producing a thin hydrodynamic film. Metal bushings struggle to build an effective film in water and tend to adhesive wear. Graphite bushings (Shore hardness 40~60 HS) form a soft-hard pairing with the steel journal; wear preferentially occurs on the graphite side, protecting the more valuable stainless shaft.

1.3 Chemical Stability and Corrosion Resistance

Submersible pump media vary widely — chloride-containing seawater, H2S-bearing sewage, acid-alkali industrial effluent. Resin-impregnated graphite is chemically inert in these media, avoiding clearance changes caused by corrosion and preserving bearing precision long-term.

1.4 Low Thermal Expansion

Carbon graphite's linear expansion coefficient is about (4~6)×10⁻⁶ /°C, only one third of stainless steel. Frequent pump starts and stops cause temperature swings that do not significantly change graphite bushing clearance, delivering better stability than plastic bushings.

2. Typical Structures of Submersible Pump Graphite Bushings

2.1 Solid Graphite Bushing

Simple and easy to machine, suitable for small and medium submersible pumps (motor power ≤ 30 kW). Wall thickness is typically 3~6 mm; clearance with the journal is 0.1%~0.15% of journal diameter.

2.2 Insert-Type Graphite Bushing

A graphite liner is pressed into a metal sleeve, combining metal strength with graphite lubricity, suitable for high-power, high-head pumps. We supply a 75 kW sewage pump with an insert bushing: outer diameter 80 mm, graphite liner 4 mm thick, interference 0.05 mm — running stably.

2.3 Segmented Three-Piece Graphite Bearing

For large vertical submersible pumps where shaft disassembly is impractical, three-segment split bearings allow in-place replacement without removing the shaft, significantly reducing maintenance hours.

3. Selection by Medium Characteristics

3.1 Clear-Water Service

Deep-well and agricultural pumps handle clean water with low solids. Resin-impregnated M106H or M120H is suitable. Parameters: temperature ≤ 40°C, PV ≤ 5 MPa·m/s. Journal hardness ≥ HRC 45; mating surface roughness Ra ≤ 0.4 μm.

3.2 Sewage Service

Sewage pumps handle fibrous and suspended matter that abrades the bushing. Antimony-impregnated M254G is preferred for its higher hardness and wear resistance. Flutes (2 mm wide, 1.5 mm deep, 6~8 axial grooves) can be cut to promote medium entry.

3.3 Seawater Service

Chloride in seawater risks corroding antimony-impregnated graphite; resin or copper-impregnated grades should be used. Journal material should be 316L stainless or duplex stainless steel, with nitrided mating surface.

3.4 High-Temperature Service

Hot-water circulation pumps may run at 90~120°C; antimony-impregnated or high-temperature resin-impregnated graphite is recommended. Increase running clearance by 0.02~0.03 mm versus room-temperature service to compensate for thermal expansion.

4. Failure Modes and Preventive Measures

4.1 Dry-Run Burns

Low water level or clogged strainers starve the bearing of medium, causing dry friction burns on the bushing — black burn marks and cracks appear. Mitigation: install low-water level switches, clean strainers regularly.

4.2 Abrasive Wear

High sand content in the medium causes three-body wear in the clearance, presenting as uniform bore enlargement and surface roughening. Mitigation: install hydro-cyclones or magnetic filters; choose harder antimony-impregnated graphite.

4.3 Galvanic Corrosion

Shaft current from variable-frequency drives may discharge through the graphite bushing, producing "washboard" ripple wear on journal and bushing. Mitigation: install a grounding carbon brush at the non-drive end to route current to the housing.

4.4 Fit Loosening

Long-term operation may loosen the outer-diameter interference fit between bushing and housing bore, causing the bushing to rotate. Mitigation: use proper interference (0.02~0.04 mm) at assembly; anaerobic adhesive may be applied if necessary.

5. Huahao Sealing Supply Case

A 90 kW municipal sewage lift pump originally used phenolic-impregnated bushings with an average life of 8 months. After switching to antimony-impregnated M254G with flutes, it ran continuously for 24 months with only 0.15 mm wear — projected to reach 30 months.

Conclusion

Submersible pump graphite bushing selection must integrate medium characteristics, pump power, operating duty, and maintainability. Huahao Sealing Co., Ltd. offers the full range of M106H resin-impregnated and M254G antimony-impregnated graphite bushings with custom-drawing support. We provide case-specific recommendations; please contact our engineering team for in-depth consultation.