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| Illustration 1 | g01023297 |
The Steering Priority Valve in Operation (1) Check valve (2) Line to implement system (3) Valve Assembly (Steering priority) (4) Spring (5) Return oil from implement system (6) Line to metering pump (7) Screen (8) Load sensing signal from steering (9) Pump supply (10) Load sensing signal from implements (11) Load sensing signal from implement system (12) Relief Valve (Load sensing signal) (13) Line to implement system (14) Check Valve (Return oil back pressure) (15) Line to tank (16) Flow Control Valve (Dump valve for the load sensing signal) | |
The manifold valve (inlet) is attached to the main control valve. The main control valve is located at the rear of the machine.
The manifold valve (implement) includes the following components:
- (1) Check valve
- (3) Valve Assembly (Steering priority)
- (7) Screens (75 and 100 micron)
- (12) Relief Valve (Load sensing signal)
- (14) Check Valve (Return oil back pressure)
- (16) Flow Control Valve Group (Dump valve for the load sensing signal)
Valve Assembly (Steering Priority)
Valve Assembly (steering priority) (3) divides the flow of oil from the hydraulic piston pump between the demands from the steering system and the demands from the implement system.
Oil from the hydraulic piston pump enters the manifold valve (inlet) and flows to the steering priority valve. The oil then flows through the open spool of the steering priority valve and flows to the metering pump through line (6) .
When the steering wheel is stationary, the spool in the steering metering unit is spring centered and the oil is blocked at the spool. The pressure then builds up in the line (6). The increased pressure acts upon the top of the priority valve spool. The spool proportionally moves down against the force of spring (4). The mid-position of the spool allows oil flow to the steering system and to the implement control system. Further movement of the spool in the steering priority valve closes off the supply of oil to the steering system. All oil flow through the priority valve is then supplied to the implement system through line (2) .
The steering priority valve ensures that the steering system has oil flow priority. When the steering wheel is turned, load sensing signal pressure is transmitted through line (8) to a chamber at the bottom of the steering priority valve. The pressure in load sensing signal line (8) combines with the force of spring (4) in order to move the spool. When the steering wheel is turned faster, the load sensing signal pressure increases in the load sensing line. The pressure determines the amount of proportional movement of the priority valve spool.
Note: Load sensing signal pressure is sometimes referred to as the signal oil. The two terms have the same meaning throughout this story.
Check Valve
Check valve (1) is a spring-loaded valve. The check valve only allows oil flow in one direction.
When the spool in the steering priority valve moves up, pressure from the top side of the spool is exhausted through check valve (1) into line (6) .
Screens
The manifold valve (inlet) of the implement control valve contains three screens (7). The screens are dedicated to the following circuits:
- The system for the pilot supply (75 micron)
- Load sensing signal system for the priority valve (100 micron)
- Drain for the load sensing signal for the implement system (100 micron)
Relief Valve (Load sensing signal)
Note: Relief Valve (Load sensing signal) is sometimes referred to as the signal limiter valve. The two terms have the same meaning throughout this story.
Relief Valve (Load sensing signal) (12) limits the load sensing signal to the pressure and flow compensator valve on the piston pump. The pressure and flow compensator valve controls the pump output pressure. The pump output pressure is proportional to the load sensing signal pressure. The relief valve has a maximum pressure setting of 22800 kPa (3300 psi).
Check Valve (Return oil back pressure)
Check Valve (Return oil back pressure) (14) is located in the return oil circuit for the main implements. The back pressure valve maintains a minimum pressure in the return oil system. The back pressure valve has a pressure setting of 3.5 ± .5 kPa (0.50 ± 0.1 psi).
Flow Control Valve Group (Dump valve for the load sensing signal)
Note: Load sensing signal pressure is sometimes referred to as signal oil. The two terms have the same meaning throughout this story.
Flow Control Valve Group (Dump valve for the load sensing signal) (16) is installed in order to provide a drain back to the hydraulic tank for the load sensing signal once the load has been reduced on the machine requirements. The drain valve is pressure compensated.