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| Illustration 1 | g00928932 |
Location of main relief valves (1) Main relief valve (2) Front control valve | |
Each section of front control valve (2) has a main relief valve (1). Main relief valves (1) limit the maximum pump discharge pressure during pressure surges. The pressure setting for main relief valves (1) is 41375 ± 350 kPa (6000 ± 50 psi).
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| Illustration 2 | g00928933 |
Main relief valve (3) Flow to front and rear control valves (4) Small spring chamber (5) Relief valve (6) Poppet | |
Pump discharge pressure enters the left end of main relief valve (1). The pump discharge pressure goes through the center of the valve spool to small spring chamber (4) which is in the center of the valve. When the pump discharge pressure exceeds 41375 ± 350 kPa (6000 ± 50 psi), poppet (6) is pushed off the poppet seat. The pressure in small spring chamber (4) drains past poppet (6) to the tank. The pump discharge pressure pushes relief valve (5) off the valve seat which opens a return passage. Pump discharge pressure flows through the passage to the hydraulic tank.
As the pump discharge pressure decreases, the spring force pushes poppet (6) to the left in order to close the passage between small spring chamber (4) and the tank. The pump discharge pressure increases in small spring chamber (4) and the pressure increase closes relief valve 5.