The load sensing differential pressure relief valves are located on the main control valve.
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| Illustration 1 | g02144007 |
Pressure differential greater than 1960 kPa (285 psi) and less than 2950 kPa (430 psi) (1) Passage (pump delivery pressure) (2) Passage (oil flow to hydraulic tank) (3) Valve (4) Passage (duplicate load sensing signal pressure) (5) Spring (6) Spring chamber (7) Passage (oil flow to hydraulic tank) (8) Spacer (0.1 mm (0.0039 inch)) (9) Spacer (0.16 mm (0.0063 inch)) (10) Spacer (0.4 mm (0.0157 inch)) | |
During normal working conditions, the pressure difference between the pump delivery pressure and the duplicate load signal pressure is maintained at 1960 kPa (285 psi) or less.
When the duplicate load signal pressure in passage (4) reaches the maximum pressure setting of the signal relief valve, the pressure in passage (1) is limited to a pressure that is 2950 kPa (430 psi) higher than the duplicate load sensing signal pressure in passage (4) .
When machine movement is stopped, the main control valve returns to the NEUTRAL position. The flow of oil from the pumps is blocked at the main control valve spool. A spike of oil pressure is created in the main feeder passage which is ported to passage (1). Pump delivery pressure acts on the left side of valve (3). The force of the pump delivery pressure shifts valve (3) against spring (5). The force of the pump delivery pressure in passage (1) is higher than the force of spring (5) and valve (3) shifts to the right. The excessive oil pressure in passage (1) is able to flow through passage (2) and passage (7) to the hydraulic tank. The duplicate load signal pressure is not created to maintain the pumps in the UPSTROKE position. The duplicate load signal pressure gradually drains to the hydraulic tank through an orifice in the main control valve spool. The gradual loss of the duplicate load signal pressure at the pump regulators allows the pumps to destroke gradually. At this time, the duplicate load signal pressure from the implement circuit is blocked from the pump regulator. Since the pumps have not destroked, the pump delivery pressure in passage (1) increases. The pressure difference between the pump delivery pressure and the duplicate load signal pressure also increases. If the differential pressure exceeds 2950 kPa (430 psi), the load sensing differential pressure relief valve operates in the following manner.
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| Illustration 2 | g02144249 |
Pressure differential less than 1960 kPa (285 psi) (1) Passage (pump delivery pressure) (2) Passage (oil flow to hydraulic tank) (3) Valve (4) Passage (duplicate load sensing signal pressure) (5) Spring (6) Spring chamber (7) Passage (oil flow to hydraulic tank) (8) Spacer (0.1 mm (0.0039 inch)) (9) Spacer (0.16 mm (0.0063 inch)) (10) Spacer (0.4 mm (0.0157 inch)) | |
The duplicate load signal pressure in passage (4) is transmitted to spring chamber (6). Spring chamber (6) is pressurized.
As the pump delivery pressure of passage (1) increases, the left end of valve (3) becomes pressurized. Valve (3) shifts to the right against the force of spring (5) and against the force of the load signal pressure in spring chamber (6) .
When the pressure difference between passage (1) and passage (4) reaches 2950 kPa (430 psi), the pump delivery flows through passage (2) and passage (7) to the hydraulic tank.