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