THEORY OF OPERATION - CONTINUED
STEERING SYSTEM - CONTINUED
Steering Control Valve. Located on the left side of the tractor, next to the scraper control valve. It is mechanically
connected to the steering control lever through the valve spool. There are three positions of the valve spool: left
turn, right turn and hold. When the steering wheel is held stationary, the valve spool is in hold position, and pump
oil in the steering control valve is routed back to the hydraulic tank. When the steering wheel is moved either left
or right, initiating a turn, hydraulic fluid is routed by the valve spool to steering cylinders, causing machine articu-
Steering Cylinder, Right Side. Receives hydraulic pressure for either extension or retraction. It causes the
machine to articulate left or right. This cylinder is mounted on the right side of the hitch and steering arrangement.
Pressure Reducing Valve. Used to produce a positive oil pressure supply from the implement pump to the follow-
up cylinder system. Oil under pressure from the implement pump is connected to the input of this valve and sent
out under lower pressure to the follow-up system. Excess oil pressure is relieved at 60 psi and returned to the
Check Valve. Allows oil from the implement pump to pass, but will not allow oil flow in a reverse direction from
the supplemental steering pump into the implement pump. In the event of engine failure or pump failure, this check
valve seals off the implement hydraulic circuit and channels all fluid from the supplemental steering pump into the
steering control valve.
FRAME, TOWING ATTACHMENTS AND DRAWBARS
Frame. The 621B Scraper is designed with reinforced box-section construction and built with extensive use of high-ten-
Tractor portion. Removable tow pin is located at front of machine, in center of front bumper.
Scraper portion. Tow hooks are located on both sides of bowl frame push block. Used for emergency towing.