Farm Machinery and Equipment. Harris Pearson Smith

soil to give traction. Numerous tests have been conducted to determine the effect of various surface conditions on tire traction. The traction efficiency for a tractor equipped with pneumatic tires is expressed as the ratio of the drawbar horsepower to the engine horsepower. This is true regardless of type of wheel equipment or tread.

      FIG. 6–21. Bar graph showing life of tractor tires in the various sections of the United States. (Farm Implement News.)

      Traction of the rear wheels on tractors is increased by adding weights to them. This is done either by attaching weights to the outside of the wheels or by filling the inner tube with liquid. If water is used in the tube, an antifreeze solution should be used where freezing conditions occur. The type of tread also is important in giving traction under different conditions (Fig. 6–22).

      Effect of Weighting Tires. Reed et al. state that “the effectiveness of tractor tires is markedly affected by the effective pressure at the bottom of the tire while under load. Higher pressures, whether caused by air or liquid, reduce the tire’s effectiveness in loose sandy soils, but increase effectiveness on concrete and extremely firm soils.” The performance of tires with three types of weights is shown in Table 6–7 and in Figs. 6–23 and 6–24.

      FIG. 6–22. Influence of type of tire tread on traction. (U.S. Department of Agriculture, Tillage Machinery Laboratory.)

      FIG. 6–23. Chart showing the increase in inflation pressure for tires filled with air, 81 per cent water, and 100 per cent water when the static load was varied from zero to 3,700 pounds. The initial inflation was 12 pounds per square inch with the tire on concrete and a static load of 2,325 pounds. (U.S. Department of Agriculture, Tillage Machinery Laboratory.)

      FIG. 6–24. Chart showing the effects of three kinds of ballast on the performance of tractor tires in packed Lakeland sand and Hiwassee sandy-loam soils. The inflation pressure was measured at the tire valve. (U.S. Department of Agriculture, Tillage Machinery Laboratory.)

TABLE 6–7. PERFORMANCE OF THREE TIRES IN TWO SOILS AT SELECTED LOADS

       REFERENCES

       Hydraulic Lifts

      Application of Hydraulic Remote Control to Farm Tractors and Trailing-type Farm Implements Standards, Agr. Engin., 32(6):328–333, 1951.

      Barger, E. L., et al.: Tractors and Their Power Units, John Wiley & Sons, Inc., New York, 1952.

      Barrett, R. D.: Determination of Loads Required to Lift Hydraulically-operated Implements, Agr. Engin., 30(10):479–480, 1949.

      Pinches, H. E.: Hydraulic Controls and Soil Conservation Implements, Agr. Engin., 31(10):514, 1950.

      Russell, George E.: Hydraulics, Henry Holt and Company, Inc., New York, 1937.

      Service and Operator’s Manuals.

      Tanquary, E. W.: Hydraulic Control for Trailing Implements, Agr. Engin., 28(3):91–94, 1947.

      ———: Application of Hydraulic Remote Control to Farm Implements, Agr. Engin., 30(1):17–19, 1949.

      Worthington, Wayne H., and J. Waldo Seiple: Hydraulic Capacity Requirements for Control of Farm Implements, Agr. Engin., 33(5):273–276, 1952.

       Rubber Tires

      Data Book, The Firestone Tire and Rubber Company, Akron, Ohio.

      Farm Tire Handbook, Goodyear Tire and Rubber Company, Inc., Akron, Ohio.

      McKibben, E. G., I. F. Reed, and C. A. Reaves: Effect of Rim Width on Tractor Tire Performance under Four Conditions, Agr. Engin., 33(8):487–490, 1952.

      Reed, I. F., G. A. Reaves, and J. W. Shields: Comparative Performance of Farm Tractor Tires Weighted with Liquid and with Wheel Weights, Agr. Engin., 34(6):391–395, 1953.

      ———and J. W. Shields: Effect of Lug Height and Rim Width on the Performance of Farm Tractor Tires, SAE Jour., 58(12):40–41, 1950.

      Rubber Tired Equipment for Farm Machinery, Ohio Agr. Expt. Sta. Bul. 556, 1935.

       QUESTIONS AND PROBLEMS

       Hydraulic Lifts

      1. Trace the development of power lifts.

      2. Give the fundamental law of enclosed liquids.

      3. A cylinder 10 inches in length and 10 inches in diameter is completely filled with oil. A pressure of 20 pounds is applied through an opening in the top. What is the total pounds pressure on the bottom?

      4. Explain the action of a gear pump.

      5. A gear pump is forcing oil into a cylinder 2 1/2 inches in diameter and 8 inches in length at a pressure of 750 pounds. What is the total pounds pressure against the cylinder piston?

      6. Explain the difference in action of a single- and a double-action cylinder. Give an application of the use of each type.

      7. Explain the functions of a master control unit and what is meant by selective controls.

       Rubber Tires

      1. Enumerate and discuss the advantages and disadvantages of pneumatic tires on farm equipment.

      2. Explain the differences in traction and free-rolling tires and the agricultural tire code system.

      3. Discuss the various factors that affect the life of agricultural pneumatic tires.

      4. Discuss the various factors that affect the traction of tires.

      ¹ Frank L. Robeson, Physics, The Macmillan Company, New York, 1943.

      ¹ Agr. Engin., 14(2):39, 1933; 16(2):45, 1935; and 17(2):73, 1936.

      CHAPTER 7

       SELECTION OF FARM MACHINERY

      Before taking up the discussion of the various individual farm implements and their construction features, it is well to stop and consider some important items that apply to all implements in general. These points or qualities that a machine may have or lack are abstract in