Hydraulic and Steering Pump
The hydraulic and steering pump is mounted to the front of the transfer gear case on the tractor. It is a two section
vane type pump. One section supplies hydraulic oil to the implements system and one section supplies hydraulic
oil to the steering system.
The cushion-hitch pump is mounted on the rear of the transfer gear case on the tractor. It is an axial piston type
pump utilizing nine pistons. The cushion-hitch pump supplies pilot pressure to the implement control valve (main
control valve), the cushion-hitch system, and the push-pull system on the Military 621G Scraper.
A steering metering pump is connected to the steering wheel of the Military 621G Scraper. The steering metering
pump is supplied with hydraulic oil from the steering control valve pressure relief circuit. When the steering wheel is
turned, the steering metering pump sends pilot oil to the spool on the steering control valve moving it left or right.
When the steering control valve spool is moved, hydraulic pressure from the hydraulic and steering pump is
diverted to the appropriate left or right steering cylinder. The steering metering pump will not give manual steering
if the engine is stopped. If the engine is stopped and the machine is moving forward, the secondary steering pump
will supply hydraulic pressure to the steering valve. Otherwise, there will be no steering function.
The operation of the steering system for a right turn is similar to the operation of the steering system for a left turn.
Pilot oil flows to the steering control valve spool. This moves the steering control valve spool to the RIGHT TURN
position. The pump oil flows to the head end of the left steering cylinder and to the rod end of the right steering cyl-
inder. This pressure oil causes the cylinders to move and the machine turns right.