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Technical Articles

Test Drive the DBS drive units
By James Hu, PE

Traditionally, the capacity and performance of a high-torque low-speed clarifier and thickener drive unit are calculated by the design engineers of the manufacturer. The results, in most cases, are good enough for typical applications. However, to optimize the drive unit design, and ensure its superior performance under the most severe service conditions, there is no better way than a dynamic load test. DBS has built a dynamometer just for that.

The DBS dynamic torque test machine measures 18 feet long, 6 feet wide and 8 feet tall. It is equipped with two long-stroke hydraulic cylinders, each is capable of 31,000 pounds of force. The body of the cylinders and the flange of the drive unit are fastened to the dynamometer frame; and the rods of the cylinders are connected to the rotating drum of the drive unit. As the drive unit turns, it pushes on the rods of the cylinders and expels the oil out of the cylinder chambers through an adjustable needle valve, which regulates the back-pressure on the cylinder pistons. The back-pressure is indicated on a pressure gauge and is used to calculate actual torque by multiplying the area of the pistons and the torque arm.

The test generates valuable information for engineers to understand how the drive unit performs under load and to verify the design against the experimental data. Through many tests, the engineers at DBS have collected a substantial amount of data, which is being compiled for design optimization. Most importantly, the integrity of the products is tested against the strictest design specifications.

Those who are familiar with field torque tests may want to know the difference between a dynamometer test and field torque test. The dynamic field test requires long-stroke cylinders similar to what are used on the dynamometer. They are heavy to transport, time consuming to set up, and expensive to perform. Therefore, most field tests are static, which only require a much lighter and simpler test rig. The static test is good for the rake and scrapers, but it tells little about the running performance of the drive. The dynamic field torque test is better, but structural deflections in the rake often confuse the results. It is also a little too late or complicated if a problem is found in the field test. The drive units that have already been calibrated on the dynamometer will not only assure success in the field test, but also allow the clarifier manufactures to conduct field torque test by simply anchoring the rakes to the clarifier floor and using the torque gauge as a load indicator.

The dynamometer has also paved the way for more extensive research: such as load sharing in multiple-pinion drive units and stresses in the main gears and pinions.