Ratio
Selection

1. Divide input rpm by output rpm to find the required gear ratio.

2. Select the closest ratio from the Horsepower and Thrust Ratings table. (Contact us if a special gear ratio is required.)

3. Proceed down the ratio column, comparing the catalog rating (at pump speed) to the requirement. Adjust the catalog rating for the required service factor if it is other than 1.5. Continue until the catalog rating is greater than or equal to the required horsepower (Interpolate for intermediate pump speeds.)

4. Verify the thrust rating of the selected gear drive to be equal to or greater than the required thrust load. Contact us if the thrust load is higher than thrust ratings given in the Horsepower and Thrust Ratings table.

5. Verify the figure of rotation with the drawings in Figure 1 - 4 below.

Example:

A solid shaft right angle gear drive is required to connect a 1800 rpm diesel engine to a 375 rpm vertical pump. The required power capacity is 780 hp with a service factor of 1.5. The pump can develop 25000 lb down thrust at duty. The horizontal shaft of the gear drive is CW and the vertical shaft, CCW.

1. Calculate the desired gear ratio 1800 / 375 = 4.8.

2. Select the closest ratio from the Horsepower and Ratings table. In this case, 5:1 ratio is the closest.

3. From this table, Model 1500A 5:1 rates 568 hp and 1800A 5:1, 880 hp (by interpolation) at 375 rpm pump speed. Model 1800A should be selected.

4. The thrust rating for Model SSL1800A at 375 rpm pump speed is 30459 lb (by interpolation), which is greater than the thrust load, 25000 lb.

5. Figure 1 should be selected for horizontal shaft rotating CW and vertical shaft, CCW.

The correct model designation would be SSL1800A 5:1. If the application requires a 1.75 S.F. instead of 1.5, we can recalculate Model 1800A 5:1 gear drive rating for the new S.F. as the following:

• Calculate the gear drive power rating with 1.0 S.F.:

P_SF1.0 = 880 * 1.5 = 1320 hp

• Calculate rating at 1.75 S.F. by dividing 1.75 into the power rating at 1.0 S.F.:

P_SF1.75 = 1320 / 1.75 = 754 hp

• Since P_SF1.75 is less than the required power rating (780 hp), the next larger model, 2200A, is considered. Model 2200A 5:1 rates 1276 hp (by interpolation) at 1.5 S.F. The rating at 1.0 S.F. is:

P_SF1.0 = 1276 * 1.5 = 1914 hp

Calculate the rating for 1.75 S.F. as:

P_SF1.75 = 1914/1.75 = 1094 hp

Model 2200A 5:1 power rating satisfies the requirement.

• The thrust rating of Model SSL2200A is 33267 lb (by interpolation), which is greater than the required thrust capacity.

If there is any question in selecting a drive, please contact us. Our engineering staff can help you select the best gear drive for your application.