The main hydraulic pump regulators use load sensing signal pressure to control pump output. There are two types of load sensing signal pressures that are used for pump control. A solenoid valve is used to select one of the load sensing signal pressures. The two load sensing signal pressures are: True Load Sensing Signal and Duplicate Load Sensing Signal.
Two separate relief valves are used to limit the duplicate load sensing signal pressure. A solenoid valve is used to select one of the two relief valves to be used for limiting the load sensing signal. The two relief valves are: Low Signal Relief and High Signal Relief.
When a travel / travel with implement function is performed, the true load sensing signal is used for pump control. The solenoid that is used to select which relief valve to use is DE-ENERGIZED. The low signal relief valve is used to limit the duplicate load sensing signal pressure. The duplicate load signal pressure is used to increase the force that is required to open the differential pressure relief valves. The differential pressure relief valves limit the main system pressure. The true load signal is also limited by the differential pressure relief valves.
When an implement function is performed, the duplicate load sensing signal is used for pump control. The solenoid that is used to select which relief valve to use is ENERGIZED. The high signal relief valve is used to limit the duplicate load signal pressure. The duplicate load signal pressure is used to increase the force that is required to open the differential pressure relief valves. The differential pressure relief valves limit the main system pressure.
HPC OFF (Travel / Travel With Implement Circuit) Low Signal Relief
 | |
| Illustration 1 | g02150724 |
Center manifold of the main control valve (front view) (1) Low signal relief valve (HPC OFF) (2) High signal relief valve (HPC ON) (3) Solenoid valve (HPC OFF or HPC ON signal relief selector) | |
Low signal relief valve (1) for the travel / travel with implement circuit (HPC OFF) is located in center manifold (18) of the main control valve.
Solenoid valve (3) is DE-ENERGIZED by the machine ECM during a travel / travel with implement operation. Duplicate load sensing signal pressure flows to low signal relief valve (1) during a travel / travel with implement operation.
Note: When solenoid valve (3) is DE-ENERGIZED, high signal relief valve (2) does not operate.
 | |
| Illustration 2 | g02150726 |
Low signal relief valve (HPC OFF) (1) Low signal relief valve (travel / travel with implement circuit) (2) High signal relief valve (implement circuit) (3) Solenoid valve (HPC OFF or HPC ON signal relief selector) (4) Signal duplication valve (5) Orifice (6) Passage (low signal pressure) (7) Passage (high signal pressure) (8) Screen (9) Screen (10) Passage (11) Passage (12) Poppet (13) Spring chamber (14) Spring (15) Adjustment screw (16) Locknut (17) Return passage (18) Center manifold (19) Locknut (20) Adjustment screw (21) Spring (22) Spring chamber (23) Poppet | |
Under a load condition of the travel / travel with implement circuit, low signal relief valve (1) operates in the following manner:
Poppet (12) is shifted downward against adjustment screw (15) by the force of spring (14). Oil flow in passage (10) is prevented from flowing past poppet (12) to spring chamber (13) .
Pressure oil flows through signal duplication valve (4). This duplicate load signal oil now flows through orifice (5). Orifice (5) eliminates the spikes in the signal. The oil now becomes duplicate load sensing signal pressure. The duplicate load sensing signal is supplied to solenoid valve (3). Solenoid valve (3) is DE-ENERGIZED by the machine ECM. The duplicate load sensing signal flows through solenoid valve (3) to passage (6). Duplicate load sensing signal flows through screen (8) and passage (6) to low signal relief valve (1) .
The duplicate load sensing signal pressure enters low signal relief valve (1). When the force of the duplicate load sensing signal pressure becomes higher than the force of spring (14), poppet (12) moves upward.
When poppet (12) moves upward, the higher pressure oil from passage (10) flows into spring chamber (13). Spring chamber (13) is ported to return passage (17) and then to the hydraulic tank. As a result, the load sensing signal pressure in passage (10) is maintained at the specified pressure setting for low signal relief valve (1) .
ReferenceFor more information concerning the pressure settings for the signal relief valves, refer to Testing and Adjusting, "Relief Valve (Signal) - Test and Adjust".
HPC ON (Implement Circuit) High Signal Relief
| | |
| Illustration 3 | g02150724 |
Center manifold of the main control valve (front view) (1) Low signal relief valve (HPC OFF) (2) High signal relief valve (HPC ON) (3) Solenoid valve (HPC OFF or HPC ON signal relief selector) | |
High signal relief valve (2) for the implement circuit (HPC ON) is located in center manifold (18) of the main control valve.
Solenoid valve (3) is ENERGIZED by the machine ECM during an implement operation. Duplicate load sensing signal pressure flows to high signal relief valve (2) during an implement operation.
Note: When solenoid valve (3) is ENERGIZED, low signal relief valve (1) does not operate.
 | |
| Illustration 4 | g02150732 |
High signal relief valve (HPC ON) (1) Low signal relief valve (travel / travel with implement circuit) (2) High signal relief valve (implement circuit) (3) Solenoid valve (HPC OFF or HPC ON signal relief selector) (4) Signal duplication valve (5) Orifice (6) Passage (low signal pressure) (7) Passage (high signal pressure) (8) Screen (9) Screen (10) Passage (11) Passage (12) Poppet (13) Spring chamber (14) Spring (15) Adjustment screw (16) Locknut (17) Return passage (18) Center manifold (19) Locknut (20) Adjustment screw (21) Spring (22) Spring chamber (23) Poppet | |
Under a load condition of the implement circuit, high signal relief valve (2) operates in the following manner:
Poppet (23) is shifted downward against adjustment screw (20) by the force of spring (21). Oil flow in passage (11) is prevented from flowing past poppet (23) to spring chamber (22) .
Pressure oil flows through signal duplication valve (4). This duplicate load signal oil now flows through orifice (5). Orifice (5) eliminates the spikes in the signal. The oil now becomes duplicate load sensing signal pressure. The duplicate load sensing signal is supplied to solenoid valve (3). Solenoid valve (3) is ENERGIZED by the machine ECM. The duplicate load sensing signal flows through solenoid valve (3) to passage (7). Duplicate load sensing signal flows through screen (9) and passage (11) to high signal relief valve (2) .
The duplicate load sensing signal pressure enters high signal relief valve (2). When the force of the duplicate load sensing signal pressure becomes higher than the force of spring (21), poppet (23) moves upward.
When poppet (23) moves upward, the higher pressure oil from passage (11) flows into spring chamber (22). Spring chamber (22) is ported to return passage (17) and then to the hydraulic tank. As a result, the load sensing signal pressure in passage (11) is maintained at the specified pressure setting for high signal relief valve (2) .
ReferenceFor more information concerning the pressure settings for the signal relief valves, refer to Testing and Adjusting, "Relief Valve (Signal) - Test and Adjust".