الأحد، 19 مايو، 2013


Hydraulic control valves in tractor
صمامات التحكم فى الجهاز الهيدروليكى فى الجرا ر                                     
1. Load check valve
2. Lift cylinder relief valve
3. Lowering metering valve
4. Lowering solenoid
5. Raise solenoid
6. Raise spool
7. Flow compensating valve


Neutral
Solenoids not energised
Oil flow from the parallel gallery A flows past the flow compensator spool into gallery B where it is blocked by the lands of the raising spool.
Oil under the pressure in the hydraulic lift circuit is prevented from entering gallery E by the load check valve (4)
The trapped pressurised oil in the lift circuit is applied to the right hand end of the metering valve through the small drilling X
The applied pressure holds the metering valve in the closed position preventing oil flow from gallery E to the return to reservoir gallery F
When the valve is in neutral , gallery C & load sensing galleries D are open to reservoir through the centre of the raising spool & gallery F.
gallery  G is a common return to reservoir gallery running through the centre of the valve stack

Lowering
Trapped oil in lift cylinder is vented through metering valve to reservoir
Lift drops with gravity and is not powered down
Drop rate is electronically controlled by the processor and solenoid
2 stages of valve movement during lowering 
Lowering
( Close up showing operation of lowering metering valve )
Stage 1
  Lowering solenoid activated
Plunger ( 1 ) and pilot spool ( 6 ) moved to right allowing trapped oil at H to go to reservoir via F past the lands in the pilot spool ( 2 )
As oil at H is released, the trapped cylinder oil E acting on the chamfered face ( 4 ), will push the metering spool  ( 3 ) to the right.
Stage 2
The lift cylinder oil can now pass the metering lands ( 5 ) of the metering spool to reservoir via F.
Drop rate is electronically controlled by the processor and solenoid which adjust the clearance over the metering lands     ( 4 ).