937
Model Code Page
61. Steering system
15. 5. 1993
6000--8750 610 9
8. 11. 1990
Priority valve (figure 7)
--- The priority valve is placed beside the pressure filter on the
RH side of the tractor.
The priority valve directs the oil flow both to the working hy-
draulics EF and to the steering hydraulics CF.
Steering hydraulics have priority. This means that in every sit-
uation there is sufficient oil flow for the steering of the tractor,
independently of the load of steering hydraulics and working
hydraulics. The rest of the oil flow is available for the working
hydraulics
Function of the priority valve:
1) The pump delivers oil---steering is not used:
The P connection of the steering valve is closed. The LS (Load
Sensing) line is connected to the T connection. All the pump
delivery is driven over the three---stepped throttling to the EF
connec tion (to the working hydraulics) with a pressure los s
determined by the LS spring, which is about 7 bar (area C x
pressure in point A=spring f orce LS).
Auxiliary pressure HP (from the low---pressure circuit, 1,8
MPa) presses the slide to the right and reduces the free---cir-
culation pressure P of the pump.
Important! From tractor ser. no. 660071 the HP pressure
does not affect the priority valve. The hose betveen the servo
valve block and the priority valve removed.
2) The steering wheel is turned:
--- T h e th r ott l e D of the steering valve opens up. The pressure
upon the steering cylinder L/R is conducted from point B
along the LS line to the spring side of the priority valve. The
pressure which acts at the left end of the slide is area Cx pres-
sure B on the steering valve (this pressure is conducted via
port CF and through the drilling on the slide). At the right end
of the slide acts pressure B + spring pressure. Now the slide
moves tothe left and oil flow between ports P --- E F is throttled
and oil starts to flow between ports P --- C F.
The state of balance is achieved when the pressure loss A --- B
= 7 bar, which corresponds to the value of the LS spring.
D is the throttling that varies according t o the steering speed
in the space A --- B :
Steering at maximum speed:
--- When the steering speed is the maximum, the flow area D
of the throttle is maximum.
The priority valve increases the oil flow from the CF connec-
tion to the steering valve so much, that the pressure loss A ---
B=7 bar. This situation correspo nds the maximum steering
speed
When the steering movement is finished, port D on the steer-
ing valve is clo s ed and the pressure in line LS discharges to
the tank. Now pressure HP presses the priority valve slide to
the right against the spring, and the oil flows from pump (port
P) to the working hydraulics (port EF). Important! From trac-
tor ser. no. 660071 the HP pressuredoes notaffect the priority
valve. The hose betveen the servo valve block and the priority
valve removed.
To Next Page
Loading...
