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