How Do Double Row Bearings Handle Axial Loads in Two Directions?

A pump shaft needs axial location in both directions. When the impeller pushes the shaft forward, the bearing must resist. When hydraulic thrust reverses during shutdown or low-flow operation, the bearing must resist again in the opposite direction. A single row of balls can only resist a limited axial load in one direction, and it cannot locate the shaft in both directions without a second bearing. This is why many pump and screw support designs use Deep Groove Ball Bearings with two rows of balls. The two rows share the axial load, one row for each direction, and the internal geometry determines how the load is distributed. This guide explains how that works and what to verify when selecting the bearing.

1. Why Does a Single Row of Balls Struggle With Axial Loads in Both Directions?

A single row deep groove ball bearing has one row of balls running in one pair of raceways. The contact angle is determined by the groove geometry and is typically small, around 10 to 15 degrees. This small contact angle gives the bearing a limited axial capacity, and the capacity is mainly in one direction because the shoulder on one side of the outer ring is higher than the other. When the axial load pushes the shaft in the direction of the low shoulder, the balls ride up the raceway and the bearing can separate if the load is too high. A bearing that must locate a shaft in both directions therefore needs two rows with symmetric shoulders, or two separate bearings mounted back to back. The second option takes more axial space and requires more careful adjustment. In our factory, we produce Deep Groove Ball Bearings in both single row and double row configurations. Cixi Hengji Bearing Co., Ltd. has been manufacturing bearings for over 12 years.

The single row design is not defective. It is simply optimized for radial load and moderate one-direction axial load. When the application requires two-direction axial location in a compact envelope, the two-row design is the more direct solution.

2. How Does the Two-Row Internal Geometry Share Axial Load in Both Directions?

A double row Deep Groove Ball Bearings has two rows of balls running in two pairs of raceways. The raceways are arranged symmetrically, so the contact angle of one row faces one direction and the contact angle of the other row faces the opposite direction. When an axial load pushes the shaft in one direction, one row carries the load while the other row is unloaded. When the load reverses, the second row takes over and the first row is unloaded. The load sharing is determined by the internal clearance and by the symmetry of the raceway shoulders. The table below shows how the axial load is distributed between the two rows under different load directions and clearance conditions.

The table shows that the two-row design does not double the axial capacity. It provides axial location in both directions, with the full axial capacity available in either direction, but not simultaneously. This is the key point that distinguishes the two-row bearing from a pair of angular contact bearings arranged face to face, where the axial load is shared between two rows at the same time. In our factory, we measure the axial load distribution on a test rig for each double row series and provide the data with the product.

3. What Happens to Contact Stress and Life When Axial Load Reverses?

When the axial load reverses, the loaded row changes. The row that was carrying the load becomes unloaded, and the row that was unloaded becomes loaded. During the transition, there is a brief period when neither row is fully loaded, and the shaft may move axially by the amount of the internal clearance. This axial movement is small, typically a few micrometers, but it can affect the contact stress distribution and the fatigue life. The fatigue life is calculated using the equivalent dynamic load, which combines the radial load and the axial load with a factor that depends on the contact angle. The table below shows the equivalent dynamic load and the estimated L10 life for different axial load levels on a 40 mm bore double row bearing.

4. Why Does the Cage and Internal Clearance Design Matter for Two-Direction Axial Duty?

The cage and the internal clearance are critical for two-direction axial duty because the bearing must operate smoothly when the loaded row changes. The cage must guide the balls in both rows without skewing, and it must withstand the acceleration that occurs when the load shifts from one row to the other. A pressed steel cage is suitable for most applications, but a machined brass cage is preferred for high-speed or high-vibration applications. The internal clearance affects the axial movement during load reversal. A larger clearance allows more axial movement, which can cause noise and impact. A smaller clearance reduces the movement but increases the risk of preload and overheating. In our factory, we offer clearance classes CN, C3, and C4, and we recommend C3 for most two-direction axial applications because it provides a balance between axial movement and thermal margin. Cixi Hengji Bearing Co., Ltd. measures the clearance of every bearing before shipment.

We also check the cage rivet tightness and the ball roundness. These details are not visible in the catalog, but they determine whether the bearing will run quietly and reliably when the axial load reverses repeatedly.

5. How Should Engineers Specify and Verify a Double Row Bearing for Reversing Axial Loads?

The specification should include the radial load, the axial load in each direction, the speed, the required life, the clearance class, and the cage type. The verification should include three tests. The first is the axial load test, which measures the axial displacement under a specified axial load in both directions. The second is the clearance measurement, which verifies that the clearance is within the specified class. The third is the temperature rise test, which verifies that the bearing does not overheat under the combined radial and axial load. In our factory, we perform these tests on a sample basis for each production lot and provide the test report with the shipment. Cixi Hengji Bearing Co., Ltd. also offers a bearing selection review for critical applications.

We recommend that the designer check the axial displacement under the reversing load. A displacement that is larger than the application allows will cause misalignment of the shaft and premature wear of the seals. The displacement is determined by the internal clearance and the elasticity of the bearing and the housing. Our application engineers can calculate the displacement for the specific mounting configuration.

Summary for Bearing Application Engineers

Double row bearings handle axial loads in two directions by using two rows of balls with symmetric raceway shoulders. One row carries the load in one direction, and the other row carries the load in the opposite direction. The axial capacity is not doubled, but the bearing provides axial location in both directions in a compact envelope. The internal clearance and the cage design determine the axial movement and the temperature rise during load reversal. The specification should include the axial load in each direction, the clearance class, and the cage type. The verification should include the axial displacement test, the clearance measurement, and the temperature rise test. Cixi Hengji Bearing Co., Ltd. has been manufacturing Deep Groove Ball Bearings for over 12 years and provides full application support for two-direction axial applications.