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the steering gear, which has been decided during designing; if the radial or axial clearance of
the stator and rotor pair is too big to cause no manpower steering, then the rotor and stator
pair should be replaced. In other conditions, adjustment is not needed.
9. Construction and adjustment of hydraulic hitch system
Hydraulic hitch system consists of hydraulic system and hitch device. Hydraulic system
is an open circulating circuit system controlled by pressure circuit. The hitch device is rear-
attached 3 point hitch. Hydraulic system mainly consists of semi-separation attachment type
hydraulic lifter, gear pump, oil filter and their oil pipes (which connect them together).
1) Working principle of gear pump
The gear pumps attached to Agracat series tractors are CBN model volume type outside
mesh gear pumps (Fig.4-15). They are all left handed pumps except the right handed pumps
on Agracat-160, 164 tractors. The gear pumps are mounted on the back end face of the right
side of the gear case of the diesel engine front, which are driven by engines. The gear pump is
made up of a pair of outside mesh shaft gear (5) and (6), gear body (2), sleeve (7) and rear
cover (1) and front cover (3).
The working principle of the gear pump is as Fig.4-16. Take left-handed gear pump as
example: After starting the engine, the driving gear of gear pump rotates counterclockwise,
and the oil enters the teeth from the pressure oil cavity and fill the teeth with oil. The oil
entered the pump is surrounded and contained by sleeve, meshed teeth and pump body and
two oil cavities which are not connected with each other are formed: suck oil cavity and
pressure oil cavity. The gear rotates right cavity (suck oil cavity) and the inner gear teeth
return mesh to make the volume between gear teeth increase and form part vaccum, and the
oil in the tank is sucked in. Meanwhile the inner gear teeth of left cavity (pressure oil cavity)
begin to mesh (teeth into each other) to squeeze the oil among the teeth out of the oil pump.
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With the rotation of the engine, the oil in the cavity will continuously flow into the lifter
through gear pump.
During working, there is pressure difference between the suck oil cavity and pressure oil
cavity of the gear pump, the high pressure oil of pressure oil cavity will leak and return to the
suck oil cavity along the clearance of the end faces of the gear and sleeve, gear tip and pump
body and the clearance formed by bad gear mesh; which will cause pump volume loss and the
heat of the hydraulic system. Too much volume loss will not make the gear pump form
normal working pressure; if seriously, the gear pump can't lift the implements.
In order to reduce the volume loss of the gear pump, complete floating sleeve is adopted
in the pump, which has hydraulic automatic compensation and axial balance construction.
During working, the sleeve can float in the pump body; the position of the sleeve is decided by
the force applied on the sleeve. The width of the pump body is 0.09-0.18mm bigger than the
width sum of gear and sleeve. After mounting, the front and rear cover are pressed tightly on
the pump body, the seal ring between the covers are compressed and the sleeve is pressed
tightly on the two end faces of the gear, thus not big clearance forms between sleeve and
covers. When the oil pressure in the gear rises, the oil pressure apply on the back of the sleeve
through the clearance (Fig.4-17), which ensures the good cooperation of the sleeve and gear
stick end faces. This action is called hydraulic automatic compensation.
2) Lifter
A. Working principle of valve (simple direction exchange valve)
The structure and working principle of the simple direction exchange valve is as Fig.4-
19.
Main control valve (1) can be respectively put on lifting, neutral and lowering positions
throughpulling operation handle (5). When main control valve (1) is on neutral position (Fig-4
-19b), the oil from the oil pump into the direction exchange valve flows back into oil tank
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through returning oil cavity A according to the flow direction designated by the arrow of the
Fig4-19(b). Then the entering oil cavity B and returning oil cavity C of the cylinder are sealed
by main control valve (1); the oil cylinder is on seal and lock condition, and the implements
are maintained in the fixed position.
When the main control valve (1) is pushed to the lowering position (Fig.4-19d) from
neutral position, the returning oil cavity C is opened, the oil in the cylinder is squeezed back
into oil tank via returning oil cavity C under the action of the weight of the implement
according to the flow direction designated by the arrow in the Fig.4-19d, then the implement
is lowering. In such case the oil from oil pump into direction exchange valve still flows back
into oil tank through returning oil cavity A.
When the main control valve is pushed to lifting position from neutral position (Fig.4-
19c), the returning oil cavity A closes, while entering oil cavity B opens. Then the oil from oil
from oil pump into direction exchange valve enters the oil cylinder via oil cavity B according
to the flow direction designated by the arrow in Fig.4-19c, and push the piston forward, then
the implement begins to rise.
System safety valve is added and established in the direction exchange valve in order to
prevent the hydraulic components from being damaged due to overload during the rising of
the implement.
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