HYDRAULIC SCRAPERS Scraper Hydraulic System Caterpillar

Scraper Hydraulic System

The scraper hydraulic system consists of a hydraulic tank (7), filters, pump (6), and control valves (4) mounted on the tractor; and lines (1), bowl cylinders (2), apron cylinder (3) and ejector cylinder (5) mounted on the scraper.

1-Lines. 2-Bowl cylinders. 3-Apron cylinder. 4-Control valves. 5-Ejector cylinder. 6-Pump. 7-Hydraulic tank.

The hydraulic tank is mounted in front of the right fender of the tractor. Two elements are used in the filter which is located in the hydraulic tank. A by-pass valve which opens at 15 PSI permits the oil to pass directly to the tank sump from the return line in event the filter elements should become clogged.

The control valve is mounted to the right of the operator's compartment. Three control levers are mounted vertically at the right of the operator and control the bowl, apron and ejector.

All high pressure hoses on the scraper are four-wire spiral wrap with permanent end fittings. The vent lines to the quick drop valves are smaller, two-wire braid hoses.

Two double acting cylinders are used to raise and lower the bowl. The bowl cylinders are double acting to provide positive down pressure for the cutting edge. A check valve and quick drop valve are mounted on the top of each bowl cylinder. The bowl carry check valve (8) acts as a safety valve in case a large hose should break or become damaged, and prevents the bowl from dropping while traveling. The quick drop valve (9) permits faster down movement of the bowl while loading. The piston rod ends of both bowl cylinders are connected by a vent hose to equalize the pressure between the cylinders.

8-Bowl carry check valve. 9-Quick drop valve. 10-Apron relief valve. 11-Apron check valve. 12-Ejector speed change valve.

One double acting cylinder is used to open and close the apron. When the apron is moved down, the system relief valve (10) controls the pressure in the piston rod end. A check valve (11) prevents the apron from floating up when the apron lever is in hold position and the bowl or ejector is operated.

A double acting cylinder is used on the ejector. An automatic speed change valve (12) is used in the ejector circuit to provide a slow and fast speed movement for the ejector. The valve changes from slow to fast depending on the resistance to the ejector created by the material in the bowl. The fast speed is obtained by automatically supplying the oil exhausted from the piston rod side of the piston to the other side of the piston along with the pump flow.

Bowl Carry Check Valve: The bowl carry check valve consists of a check valve located at the top of the bowl cylinders. This check valve blocks the oil passages when the bowl control lever is in hold position, and traps oil in the bowl cylinders.

The bowl is held by the blocked oil in the cylinders rather than by system pressure. This eliminates the need for high pressure in the hydraulic lines while the machine is traveling. Should a large hose break or become damaged, the blocked oil in the bowl cylinders will prevent the bowl from dropping.