Case 580SR Service Manual page 643

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Circuit relief valves operating
Relief valve inoperative
When the system is not subject to overload condi-
tions pressure in the system is insufficient to over-
come pilot valve spring pressure and move the valve
of its seat.
System pressure sensed on the larger rear face of
the poppet valve maintains the poppet and sleeve
firmly on their seats.
1. Sleeve
2. Poppet valve
3. Pilot valve
4. Pilot valve body
5. Piston
6. Control valve (cylinder) exhaust gallery
7. Cylinder supply gallery
Pilot valve operation
When the cylinder is subjected to shock forces, the
pressure increase in the cylinder supply gallery ex-
ceeds the pilot valve spring pressure: this valve lifts off
its seat. System pressure on the rear face of the poppet
valve escapes to tank between the sleeve poppet and
valve body causing a pressure differential between the
front and rear face of the poppet valve. The higher pres-
sure in the cylinder supply gallery unseats the poppet
valve and moves the piston to seat against the pilot
valve.
1. Sleeve
2. Poppet valve
3. Pilot valve
4. Pilot valve body
5. Piston
6. Control valve (cylinder) exhaust gallery
7. Cylinder supply gallery
Pilot and poppet valve operation
The excessive system pressure in the cylinder sup-
ply gallery now flows past the poppet valve to the
cylinder exhaust gallery and back to tank.
NOTE: during this operation the sleeve poppet is
held in the fully seated position by pressure oil.
1. Sleeve
2. Poppet valve
3. Pilot valve
4. Pilot valve body
5. Piston
6. Control valve (cylinder) exhaust gallery
7. Cylinder supply gallery
SECTION 35 - HYDRAULIC SYSTEM
1 2
7 6 5
Exhaust oil
High pressure oil
1 2
7 6 5
Exhaust oil
High pressure oil
Reduced pressure oil
1 2
7 6 5
High pressure oil
Exhaust oil
Reduced pressure oil
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3
4
F29539
3
4
F29540
3
4
F29541