I. Core Principle: The ball is the "heart" of the bearing
The performance of the ball directly determines the bearing's load-bearing capacity, rotational speed limit, lifespan, noise level and corrosion resistance. When choosing, the following key factors should be considered:
Material - This is the most important factor
High-carbon chromium bearing steel (GCr15): This is the most commonly used and cost-effective bearing steel material, suitable for the vast majority of ordinary water pump bearings. It has high and uniform hardness, excellent wear resistance, and contact fatigue strength.
Stainless steel (such as AISI 440C, 304):
440C (9Cr18) martensitic stainless steel: It possesses stainless properties, and its hardness and wear resistance are comparable to those of GCr15. It is the preferred choice for corrosion-resistant bearings and is suitable for applications such as submersible pumps, sewage pumps, seawater pumps, etc., in environments with moisture and corrosive media.
304 (0Cr18Ni9) Austenitic Stainless Steel: It has better corrosion resistance than 440C, but has lower hardness and poorer load-bearing capacity and wear resistance. It is usually used in low-load and highly corrosive applications, such as food pumps and some shallow water submersible pumps.
Ceramics (mainly silicon nitride Si3N4):
Advantages: Low density (light weight), extremely high hardness, absolutely insulating, corrosion-resistant, high temperature-resistant. It can significantly reduce centrifugal force at high speeds, minimize wear, and extend lifespan.
Disadvantages: Extremely high price, high brittleness, poor impact resistance.
Application: High-end, high-speed spindles, extremely harsh corrosive environments or special scenarios requiring insulation (such as water pumps driven by frequency conversion motors). This is extremely rare in ordinary water pumps.
Manufacturing process and precision grade
Accuracy: The size accuracy of the steel balls (true roundness, diameter variation), and the surface finish (roughness) are classified into levels such as G3, G5, G10, G16, G20, G24, G28, G40, G60, G100, etc. The smaller the number, the higher the accuracy.
Impact on bearings: The higher the precision of the steel balls, the higher the rotational accuracy of the bearing, the lower the vibration and noise, the lower the temperature rise, and the longer the lifespan. Water pump bearings usually use G10 or G16 grade steel balls, which can meet the needs of most industrial applications. High-precision water pumps (such as machine tool cooling pumps) may require higher precision.
Heat treatment
The steel balls must undergo a heat treatment process of quenching + low-temperature tempering to achieve high and uniform hardness (usually above HRC 60). The level of the heat treatment process directly determines the fatigue life and wear resistance of the steel balls.
II. Guide for Selecting Steel Balls (Bearings) Based on Different Pump Operating Conditions
As a user, your choice lies in selecting the appropriate bearing. The table below correlates the pump operating conditions with the requirements for bearings (steel balls):
Pump operating condition
Recommended bearing (indirectly determining the steel balls)
Steel ball material and key characteristics of bearings
General-purpose clean water pump (at normal temperature, clean water)
Deep groove ball bearings (6000, 6200, 6300 series)
Steel ball: GCr15 high-carbon chromium bearing steel
Sealing: ZZ (metal dust-proof cover) or 2RS (rubber contact type seal)
This is the most economical and commonly used option.
Submersible pumps, sewage pumps, seawater pumps (high humidity, corrosive)
Stainless steel deep groove ball bearing
Steel ball: 440C stainless steel
Spacers: Engineering plastics (such as PPS), stainless steel
Sealing: High-performance rubber sealing to ensure optimal waterproof and moisture-proof performance.
Core requirement: Corrosion resistance.
High-temperature water pump (hot water circulation, hot oil pump)
High-temperature bearing
Steel balls: Usually still made of GCr15, but the bearings will undergo high-temperature stabilization treatment and use high-temperature lubricating grease (such as polyurea grease).
Inner rings: May require the use of copper alloys or special polymers.
Heavy-duty load pumps (multi-stage pumps, slurry pumps)
Angular contact ball bearings (7000 series) or tapered roller bearings
Steel ball: GCr15, but the bearing design can withstand combined loads.
This type of pump has significant axial force, so a specific type of bearing capable of withstanding axial force needs to be selected. The size and arrangement of the steel balls are different from those of deep groove ball bearings.
High-speed pumps with special requirements
Mixed ceramic bearing
Steel ball: Silicon nitride ceramic Si3N4
Inner and outer rings: Still made of bearing steel (GCr15) or stainless steel (440C)
Advantages: Excellent high-speed performance, long lifespan, corrosion resistance. However, the price is dozens of times that of ordinary bearings.
III. Practical Suggestions for Maintenance/Procurement Personnel of Feedwater Pumps
You do not need to purchase the steel balls separately. Instead, focus on the following points:
Choose a reliable bearing brand:
International leading brands: SKF (Skefco), FAG/INA (Schaeffler), NSK (Seiko), TIMKEN (Timken). These brands have strict standards in terms of materials, heat treatment and manufacturing processes, and the quality of their steel balls is guaranteed.
Domestic well-known brands: HRB (Harbin Bearing), ZWZ (Wuhan Bearing), LYC (Luoyang Bearing). These are outstanding domestic products with high quality and good cost-effectiveness, capable of meeting the needs of most water pumps.
Carefully choose not to use cheap bearings of unknown origin. Their steel balls, heat treatment, and precision may not meet the standards, which is the main cause of early failures of the water pump.
Clearly define the bearing code: When ordering or replacing bearings, provide the complete bearing model and accuracy grade.
For example: 6204-2RS C3
6204: Dimension code (inner diameter 20mm)
2RS: Double-sided with rubber sealing rings
C3: The internal clearance is greater than that of the standard grade, and it is suitable for applications with higher temperature rise.
Correct installation and maintenance: Even the best steel ball bearings can be damaged rapidly due to incorrect installation (such as improper striking), poor lubrication, or failure of the seal.
Summary
When choosing the bearing balls for the water pump, it can be simplified as:
Normal situation: Select standard bearings made of GCr15 bearing steel from well-known brands.
Damp and corrosive environment: Select stainless steel bearings made of 440C stainless steel.
Extreme operating conditions (high speed, high temperature, strong corrosion): Consider special bearings such as composite ceramic bearings.
Ultimately, by choosing high-quality bearings suitable for the specific application, you have already selected the most compatible and reliable "balls" for the water pump. The selection of the balls is more the responsibility of the bearing manufacturer.
