When choosing the grease for the pump bearings, the following core factors need to be taken into consideration:
Water resistance
Importance: This is the primary consideration under the pump's operating conditions. The pump itself deals with water or other liquids. The environmental humidity is high, and if there is any slight failure in the bearing seal, moisture or water vapor may enter the bearing interior.
The oil must have excellent resistance to water erosion (not easily washed away by water) and rust and corrosion prevention properties. The oil should be chosen that has strong adhesion and can form a protective film.
Mechanical stability (resistance to shear)
Importance: The bearings of pumps usually operate continuously, and the grease is subjected to continuous mechanical shear forces. If the mechanical stability is poor, the grease will become soft, thin, and even separate the base oil, resulting in the separation of oil and soap, and losing its lubrication and sealing functions.
Select an oil with good mechanical stability to ensure that it can maintain its original consistency and structure even under long-term shear.
Viscosity (NLGI grade)
Importance: The concentration level determines the softness and fluidity of the oil, as well as its pumpability.
Common choice: The majority of pump bearings are recommended to use NLGI 2 grade or NLGI 3 grade lubricating oil. NLGI 2 grade is the general choice and is suitable for most conditions. In vertical pumps or high-temperature environments, a harder NLGI 3 grade lubricating oil may be selected to prevent oil leakage.
Working temperature range
Importance: The grease must be able to cover the entire temperature range during the startup and operation of the pump.
Base oil type:
Mineral oil: Suitable for normal temperatures (such as -20℃ to 120℃). It is sufficient for most normal temperature water pumps.
Synthetic oil (PAO/ester oil): Suitable for a wider temperature range (such as from -40℃ to above 150℃), with longer lifespan and better oxidation stability at high temperatures. Suitable for high-temperature water pumps, hot water circulation pumps, or environments with significant temperature fluctuations.
Base oil viscosity
Importance: The viscosity of the base oil determines the ability of the lubricating film to form between the rolling elements and the raceways of the bearing. If the viscosity is too low, an effective oil film cannot be formed, which will lead to wear; if the viscosity is too high, it will increase the running resistance and cause temperature rise.
Selection: It needs to be matched based on the bearing size, rotational speed (DN value), and load. Pump bearings are usually for medium-low speed and medium-light load. The commonly used base oil viscosities are between ISO VG 100 and 150.
II. Common Types of Thickening Agents and Their Applicability
The type of thickening agent is the key to differentiating the properties of oils.
Lithium-based composite soap (Lithium Complex)
Feature: It is currently the preferred and most commonly used type of pump bearing.
Advantages: It has excellent water resistance, mechanical stability and wide temperature performance (compared to ordinary lithium-based products). It is a versatile and high-performance option.
Applicable t The vast majority of industrial water pumps, water supply pumps, irrigation pumps, etc.
Polyurea
Feature: A common choice for high-performance synthetic lubricants.
Advantages: Excellent oxidation stability and high-temperature durability (longer lifespan than lithium-based composite grease at high temperatures), low noise.
Disadvantages: Poor compatibility with certain other types of oils. When changing the oil, it is necessary to thoroughly clean the old oil. Higher price.
Applicable t High-temperature water pumps, pumps with high requirements for long service life and maintenance-free operation, and motor bearings.
Calcium-based composite soap (Calcium Complex)
Features: Known for its excellent adhesion and water resistance.
Advantages: Particularly suitable for humid and water-spraying environments.
Disadvantage: The high-temperature performance is usually not as good as that of lithium-based composite grease and polyurea grease.
Applicable t Submersible pumps, sewage pumps, etc., for harsh working conditions where they come into direct contact with water.
Ordinary Lithium Base (Lithium Soap)
Feature: General-purpose lubricant with balanced performance.
Applicable: It can still be used for pumps with moderate requirements and normal operating conditions, but it is highly recommended to upgrade to lithium-based composite grease for better overall performance. References for common brands and models (example)
Kluber (Klüber): Klüberspeed GHY 72 (High-performance polyurea-based grease, suitable for high-speed and high-temperature applications)
Shell: Gadus S3 V220C (Lithium-based composite grease, widely used in water pumps)
Total: Multis 2 (Multifunctional Lithium-Based Composite Grease)
Great Wall Lubricant: Great Wall Grease AE Series (Lithium-based Composite Grease, a top-notch domestic product)
Note: For specific models, please refer to the technical data provided by the supplier. The above examples are merely common cases.
V. Key Points for Use and Maintenance
1. Cleaning: Before adding new grease, ensure that the oiling nozzle and the bearing area are clean to prevent impurities from entering.
Do not mix: Different brands and types of oils must not be used together, except when there is a manufacturer's compatibility guarantee. Mixing incompatible oils will result in a significant decline in performance. When changing the oil, the old oil must be completely removed.
Appropriate filling: The amount of grease added to the rolling bearing chamber is usually 1/2 to 2/3 of the space. Overfilling will cause the bearing temperature to rise, which in turn shortens its lifespan.
Establish a lubrication plan: Based on the operating time and environment of the pump, formulate a plan for regular replenishment or replacement of the lubricating oil.
Summary
For the majority of pump bearings, choosing a lubricating grease that is based on synthetic oil, uses lithium-based composite soap as the thickener, has a NLGI 2-grade consistency, and contains anti-wear and anti-corrosion agents is a safe, reliable and high-performance option. If there are special requirements for the working conditions (such as extreme temperatures, food-grade), then specific polyurea-based or food-grade greases should be selected accordingly.
Ultimately, the most reliable approach is to refer to the official recommendations provided by the pump equipment manufacturer (OEM) and make the best choice based on the actual working conditions.
