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Farm equipment prior to the nineteenth century era was animal drawn, guided by hand, and lifted manually. Later, when equipment was mounted on wheels, levers were used to raise and lower the working units. The first mechanical power-lift was developed for the trailing-type tractor-drawn plows about 1910 (Fig. 6–1). The tractor power lift was developed about 1930 to raise and lower planters and cultivators mounted on the row-crop tractor. The use of hydraulic power for lifting tractor-mounted equipment was introduced in 1933. Hydraulic power lifts are now used for raising, lowering, and controlling almost all types of field equipment, ranging from the small plow to the platform of a grain combine and the drums of cotton-picking machines. In fact, if it were not for the hydraulic lifts, these heavy units would be extremely difficult to operate.

FIG. 6–1. A mechanical power lift for plow.

The extensive use of hydraulic lifts and controls makes it essential that the operator of modern farm equipment have an understanding of the fundamental principles of power-lift hydraulics.

Fundamentals of Hydraulics. There are several branches of hydraulics, but the branch applicable to farm equipment deals with enclosed liquids under pressure. The fundamental law of hydrostatics, or the mechanics of fluids, was defined by Blaise Pascal¹ in 1653 as follows: “Pressure applied to an enclosed fluid is transmitted equally and undiminished in all directions to every part of the fluid and of its restraining surfaces.” The application of this law is shown in Figs. 6–2 and 6–3. In Fig. 6–3 is a 1-pound weight acting on 1 square inch of liquid which is counter-balanced by a weight of 10 pounds on 10 square inches of liquid. There is a 1-pound pressure for each square inch of surface on all sides of the container. The 1-inch piston must move 10 inches to move the 10-square-inch piston 1 inch.

Oil Pumps. Pumps are required in the operation of hydraulic controls to draw the oil from a reservoir and force it into a cylinder. The pump may be of three types, namely, gear, vane, and piston.

FIG. 6–2. How pressure on a liquid distributes pressure in all directions of its enclosure case. (International Harvester Company.)

A typical rotary double-gear pump consists of two closely meshing gears enclosed in a tight, compact housing. There are intake and discharge ports on opposite sides of the housing. When they rotate as indicated in Fig. 6–4, the oil is drawn in through the intake port and caught in the spaces between the gear teeth and the housing. The oil is carried around by the gear teeth and forced out through the discharge port. When the gears are rapidly rotated, a partial vacuum is created which draws oil from the reservoir.

A vane-type oil pump is shown in Fig. 6–5. The rotor has a number of radial slots into which movable vanes are fitted. As the rotor revolves, the vanes are forced outward by centrifugal force and oil pressure against the surface of an oval-shaped ring. The vanes follow the inside cam contour as they rotate. The oval ring is so shaped that two opposing pumping chambers are formed on opposite sides of the rotor. The oil is drawn in on one side and forced out on the opposite side. The pump gives a continuous flow of oil when the tractor engine is operating.

Piston oil pumps may have as many as four small plunger pistons operated, in most cases, by cams. A variable delivery of oil may be obtained by closing the ports to one or more of the pistons.

FIG. 6–3. A simple hydraulic system with a 1-pound weight on 1 square inch has the same pressure per square inch as the 10-pound weight on a piston resting on 10 square inches of liquid. There is also a 1-pound pressure on the gage. (International Harvester Company.)

When the pump and the cylinders are connected (Figs. 6–6 and 6-7) by means of steel pipe or high-pressure hose, oil can be pumped into power cylinders located either near, or at a considerable distance from, the pump. The oil reservoir and pump may be located at some point within the tractor housing (Fig. 6–8) or at some convenient place outside the housing (Figs. 6–9 and 6-10). In either case, the hydraulic pump and system become a component part of the tractor. As oil pumps operate continuously, a by-pass is essential to permit oil to return to the reservoir when no pressure is required in the lifting cylinders.

FIG. 6–4. Cross section of a rotary-gear pump. (International Harvester Company.)

Hydraulic Cylinders. Hydraulic cylinders are also called rams and jacks. When hydraulic force is applied through especially designed cylinders and connections, farm equipment can be lifted, lowered, and controlled easily. The ASAE standards give the dimensions and specifications of hydraulic cylinders for remote control of trailing farm implements. The recommended length of stroke for such cylinders is 8 inches. Figure 6–6 shows how pressure is exerted on a piston inside a cylinder when oil is pumped into the cylinder. A cylinder 3 inches in diameter is approximately 7 square inches in cross-sectional area. Therefore, if oil is being forced into the cylinder with a pressure of 800 pounds, the pressure against the face of the piston is 800 × 7, or 5,600 pounds. If the cylinder is fastened to a rigid part of a machine at A and the piston rod B connected to a crank arm, the machine can be lifted with 5,600 pounds pressure. Figure 6–7 shows a schematic diagram of how hydraulic power cylinders can be used to lift units, such as cultivator gangs.

FIG. 6–5. End view of vane-type oil pump with oval ring and rotor with sliding vanes. (Vickers, Inc.)

FIG. 6–6. Simple diagram showing how a gear-pump pumps oil from a reservoir of oil to a power cylinder. (International Harvester Company.)

Figures 6–11 and 6–12 show two-way or double-action cylinders designed so that oil pressure can be applied to either side of the piston, and thus exert power in two directions. This type of cylinder is used to control plowing depth and to angle and de-angle tandem disk-harrow gangs. Stop yokes on hydraulic cylinders are provided to shorten the length of the cylinder stroke from the full, standard 8 inches to 0 on some cylinders, as desired. Where several inches of movement are required, long hydraulic power cylinders with long piston rods can be used (Fig. 6–13).

FIG. 6–7. Schematic diagram of a hydraulic-lift system where oil is being pumped into two lifting cylinders. At this stage the pressure is not high enough to open the delayed lift valve on the rear cylinder. (International Harvester Company.)

Tables 6–1 and 6–2 show the maximum pounds pressure required in a hydraulic cylinder to lift various sizes of moldboard and disk plows. The maximum pressure to angle different sizes of tandem disk harrows is shown in Table 6–3. The cylinder pressure necessary to lift or control the implements is shown for both moving and stopped positions.

FIG. 6–8. Some hydraulic-lift systems have the pump and power cylinder enclosed in the tractor housing. The parts are as follows: A, control spring; B, control lever; C, cylinder piston; D, hydraulic pump; E, control and safety valves; F, lift crank; G, lift link. (Harry Ferguson, Inc.)

FIG. 6–9. Schematic diagram of hydraulic-lift system for a cotton picker, showing hydraulic pump, oil reservoir, a system of passages and valves to direct the flow of oil to raise cotton-picker drums and to tilt the basket. (John Deere.)

FIG. 6–10. Schematic diagram showing hydraulic oil pump, hose lines, and power cylinders, for operating lift shaft and crank arms, mounted as component parts of the tractor, and optional use of a remote-control cylinder. (Allis-Chalmers Mfg. Co.)

FIG. 6–11. A portable double-action hydraulic cylinder equipped with a stop or adjusting yoke for setting the tandem disk harrow to different degrees of cutting angle. (John Deere.)

FIG. 6–12. Portable hydraulic-lift cylinder equipped with stop yoke attached to trailing plow so that adjustment can be made for uniform plowing depth. (J. I. Case Company.)

Worthington and Seiple found that the minimum values of drawbar horsepower per plow bottom form the most consistent index of power requirement for tractor sizes rated to operate two to five bottoms. Tractors of a given drawbar horsepower can operate larger and heavier implements under favorable conditions than they can under unfavorable conditions. Therefore, it follows that any matching of tractor-drawbar performance with accompanying hydraulic-cylinder lifting effort may properly be on the basis of minimum tractor power and maximum cylinder thrust for each implement-tractor group as shown in Table 6–4.

Master Control Units. The master control mechanism that directs the flow of oil to the various power cylinders may be located either within the tractor gear case or at some convenient place outside the gear case. These units consist of a system of passages, control valves, check valves, regulator valves, safety valves, and pistons (Fig. 6–8). These systems are called many different names, such as touch-control, touch-o-matic, lift-all, power-trol, and power-pack. These control units are assembled and installed at the factory. Control units are used on self-propelled grain combines and cotton-picking machines (Fig. 6–9).

Selective Control. The selective control of a hydraulic-lift system provides individual control of the right- and the left-hand-mounted units separately and the front and the rear units separately. This is done by the use of delayed lift (Fig. 6–14) and retarding valves to regulate the flow of oil to and from the remote cylinder. In a master control system, the flow of oil to the various cylinders is regulated by opening and closing an arrangement of valves and passages.

FIG. 6–13. Long hydraulic cylinders with long piston rods are used where several inches of movement are needed. (John Deere.)

There are many types of master and selective control systems. Each manufacturer has a particular design and application of hydraulic power controls. The operator should obtain service literature for the make of his equipment and carefully study it before making adjustments. Major repairs should be done by a trained serviceman.

TABLE 6–1. CYLINDER PRESSURE OR THRUST REQUIREMENTS FOR MOLDBOARD PLOWS EQUIPPED WITH 12-, 14-, AND 16-INCH BOTTOMS

* The disproportionate increase in the cylinder thrust necessary to raise the five-bottom plow reflects the heavy duty imposed by implements built with sufficient strength for operation with crawler tractors. W. H. Worthington and J. W. Seiple, Agr. Engin., 33(5):273–276, 1952

Accessories for Hydraulic Controls. When the oil pump and controls are located on the tractor, and the hydraulic-lift cylinder at a remote distance on a trailing implement, high-pressure hose of sufficient length must be provided to permit required turns (Fig. 6–12). The hose should be of a quality to resist oil deterioration, to withstand high pressures, and to work at a wide range of temperatures. The data in Table 6–5 show the specifications for one make of hose.

Should a trailing machine equipped with a remote-control hydraulic cylinder, such as a plow, break away from the tractor a safety breakaway coupling should be provided to prevent damage or breaking of the hose. A breakaway coupling is shown in Fig. 6–15.

The hose between the tractor and the implement should be provided with adequate supports to protect the hose.

FIG. 6–14. A cross-sectional view of a delayed lift valve. A pressure of 425 to 475 pounds per square inch is required to lift the valve off its seat and permit oil to flow into the cylinder. This valve is installed on the end of the hose next to the lift cylinder, as shown. (International Harvester Company.)

When implements are interchanged frequently, much time can be saved by the use of snap-on hose connections (Fig. 6–16). Special care should be taken to keep all hose connections clean. When disconnected hose is to be left unused, the ends should be wrapped with a rag to keep dirt and sand from getting in the hose. A grain of sand can cause serious valve trouble.

TABLE 6–2. CYLINDER THRUST REQUIREMENTS FOR DISK PLOWS 24, 26, AND 28 INCHES IN DIAMETER

* The severe lifting requirement of the heavy-duty-type implements is evidenced. W. H. Worthington and J. W. Seiple, Agr. Engin., 33(5):273–276, 1952.

TABLE 6–3. CYLINDER THRUST REQUIREMENTS FOR TANDEM OR DOUBLE-ACTION DISK HARROWS

SOURCE: W. H. Worthington and J. W. Seiple, Agr. Engin., 33(5):273–276, 1952.

TABLE 6–4. MINIMUM HYDRAULIC CYLINDER THRUST FOR VARIOUS IMPLEMENT-TRACTOR GROUPS

TABLE 6–5. SPECIFICATIONS FOR HIGH-PRESSURE HOSE

* At maximum working pressure.

Fig. 6–15. Breakaway coupling for trailing equipment: top, shows coupling connected; bottom, shows the tractor and implement sections separated. (Aeroquip Corp.)

Hydraulic-Electric Lift. The company that developed this system terms it a Hydra-Lectric system. The operation is described as follows:

Located within the fluid reservoir are one or two solenoid-actuated selector valves depending upon whether one or two cylinders are being used. Each selector valve has an up and a down “coiled” solenoid, arranged coaxially and having a common metal plunger. When either up or down solenoid is energized, it moves the solenoid plunger in a respective forward or backward direction. Through a crank arrangement, the plunger actuates a spool-type selector valve which opens and closes parts that control the direction of fluid flow to the cylinder to produce an outward or inward stroke of the piston rod. When the selector valve is moved to a neutral position, the flow of fluid to the cylinder is shut off and is directed back to the reservoir. A spring and ball controlled interlock valve then traps the fluid leading to the cylinder and holds the piston rod in a stationary position.

FIG. 6–16. Snap-on quick coupler for hydraulic hose. (Bruning Company.)

The system can be used to control either mounted or trailing equipment.

Special Hydraulic Applications. Hydraulic cylinders have many applications in special jacks, truck and trailer box lifts, utility hoists, loading attachments, and steering aids.