THEORY OF OPERATION - CONTINUED
ELECTRO-HYDRAULIC SYSTEM - CONTINUED
Main Load Sensing Relief Valve.
Standard main control valve is equipped with one main relief valve which limits oil pressure to main hydraulic sys-
tem from implement pump.
When pressure at inlet of main control valve exceeds pressure setting of main relief valve, main relief valve opens.
Excess hydraulic oil then flows through main relief valve to hydraulic tank.
Main relief valve is a direct operated cartridge type valve with a pressure setting of approximately 4,500 ± 100 psi
(31,000 ± 690 kPa).
Implement system oil flows into inlet, causing poppet to unseat. Oil then drains back to tank through outlet.
When oil pressure in circuit is greater than relief valve setting, oil pressure overcomes force of poppet spring, caus-
ing poppet to unseat. Oil will then flow out of outlet and back to hydraulic tank. Simultaneously, oil will flow
through a passageway in poppet and into spring chamber.
Oil pressure in spring chamber will stabilize poppet during relief valve operation.
When oil pressure in circuit is less than relief valve setting, force of spring keeps poppet closed.
Relief valve setting can be adjusted by changing force of spring keeping poppet closed. Loosen locknut and turn
plunger clockwise to increase relief valve setting. Turning plunger counterclockwise decreases relief valve setting.