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
• 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
• 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
( Close up showing operation of lowering metering valve )
• 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.
• 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 ).