STEERING AND SCRAPER HYDRAULICS CONTINUED
The Military 621G Scraper implements system controls the ejector cylinder, bowl cylinders, and apron cylinder. The
implements are supplied hydraulic oil pressure from the hydraulic and steering pump. Pilot pressure is supplied by
the cushion-hitch pump. The implements are controlled by a 3-spool main control valve, pilot pressure, and an
electronic implement control lever. The implement control lever sends an electronic signal to a solenoid mounted
on the main control valve. The solenoid actuates allowing pilot pressure to move a spool in the main control valve.
The spool then allows hydraulic oil to flow to the corresponding cylinder.
The cushion-hitch connects the tractor and the scraper. The cushion-hitch works as a shock absorber between the
scraper and the tractor using hydraulics and pressurized nitrogen gas to minimize vertical movements of the Mili-
tary 621G Scraper. The cushion-hitch can be turned on and off. The cushion-hitch should always be turned on,
except when material is being loaded and unloaded.
The cushion-hitch system has eight major components:
Hitch hydraulic accumulator valve
Upper link assembly
Lower link assembly
The hitch assembly
The bracket assembly is attached to the scraper. The hitch assembly is connected to the tractor. The upper link
assembly and lower link assembly connect the bracket assembly and the hitch assembly. The load cylinder also
connects to the bracket assembly and to the hitch assembly. A switch in the cab sends an electronic signal to a
solenoid on the hitch hydraulic accumulator valve to activate the cushion-hitch system.
When the cushion-hitch switch is turned ON, hydraulic oil is pumped by the cushion-hitch pump to the hydraulic
accumulator and the head end of the load cylinder extending the cylinder. As the load cylinder extends, the bracket
assembly is lifted off the hitch assembly. The bracket assembly now rides on a cushion of hydraulic oil that sepa-
rates the bracket assembly from the hitch assembly. The hitch hydraulic accumulator valve controls hydraulic flow
between the load cylinder, hydraulic accumulator, and the cushion-hitch pump. It is set to maintain a specific height
between the hitch assembly and the bracket assembly. The hitch hydraulic accumulator valve stops hydraulic flow
from the cushion-hitch pump to the load cylinder. Hydraulic fluid can flow freely between the hydraulic accumulator
and the load cylinder. The free flow of hydraulic fluid between the hydraulic accumulator and the load cylinder pro-
vides a cushioned ride.