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| Illustration 1 | g00465115 |
Location of the priority valve | |
The priority valve is mounted on the lower left side of the bevel gear case.
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| Illustration 2 | g00462174 |
Components of the priority valve (1) Torque converter inlet relief valve (1A) Relief valve spool (2) Passage to torque converter (3) Passage to bevel gear case (4) Relief valve spring (5) Relief valve adjustment (6) Priority valve adjustment (7) Priority valve spring (8) Priority valve (8A) Priority valve spool (9) Passage from the torque converter and lubrication section of the pump (10) Slug chamber (11) Supply chamber (12) Slug | |
The torque converter inlet relief valve (1) is a unit of the priority valve.
The priority valve makes sure that oil pressure is first available for braking and for transmission control. As the next priority, the priority valve supplies oil to these uses: torque converter, lubrication for the brakes and lubrication for the transmission.
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| Illustration 3 | g00462176 |
(1) Torque converter inlet relief valve (5) Relief valve adjustment (6) Priority valve adjustment (8) Priority valve (13) Solenoid valve | |
Valve Operation
The priority valve setting is determined when solenoid valve (13) selects oil from either inlet (9) or drain (3) in order to supply oil to chamber (11) .
Oil from section (A) of the power train oil pump enters inlet passage (9) in the priority valve.
The oil goes from inlet passage (9) through a hole in valve spool (8A). The oil then goes into chamber (10) between the slug and the poppet.
When the oil pressure in chamber (10) becomes higher than the priority valve setting in the current mode of operation, valve spool (8A) moves. The valve spool moves toward adjusting screw (6). Then, pressure oil flows to outlet passage (2) .
The pressure oil goes from outlet passage (2) to the torque converter. The oil then goes through the oil cooler. From the oil cooler, the oil goes to the brakes in order to provide lubrication. The oil also provides part of the lubrication for the transmission.
The priority valve has two modes of operation: normal mode and priority mode.
Normal Mode
In the normal mode, flows for the torque converter and for lubrication are separate. The brakes and the transmission do not have priority.
For the normal mode, the solenoid is ON and inlet (9) is selected.
In the normal mode, inlet pressure in chamber (11) acts on more of the spool area around slug (12). Then, valve spool (8A) moves toward adjusting screw (6). Oil from the torque converter and lubrication section of the pump passes through the priority valve to the torque converter.
Priority Mode
In the priority mode, oil supplies to the torque converter and to the lubrication system have priority in order to maintain pressure for braking and for transmission control.
For priority mode, solenoid (13) is OFF and drain (3) is selected.
In priority mode, the pressure in supply chamber (11) is drained. Then, the inlet pressure in slug chamber (10) moves valve spool (8A). The inlet pressure that is required is the pressure setting for the priority valve.
Conditions for Priority Mode
The electronic control module controls the current to the solenoid.
No current is sent to the priority valve under specific operating conditions in order to maintain adequate pressure to the brake controls and to the transmission controls. The priority valve is at high pressure in this mode.
No current is applied to the priority valve during the following conditions:
- Engine speed that is less than 1300 RPM
- Power train oil temperature less than 40°C (104°F)
- Transmission shift in progress
- Calibration for transmission in progress
This setting can be adjusted by turning adjusting screw (6) and locking the adjusting screw in place with the locknut.
Reference: Refer to the procedure in Testing and Adjusting, "Priority Valve - Adjust" in the Service Manual for your machine.