Although the valves act in conjunction with each other in the system, their operation can be considered separately.
The Primary regulating valve has a number of lands, including one larger land which provides a differential area.
A central stem locates the regulating spring.
Fluid from the pump can act on the valve through a 1-millimetre diameter orifice in the circuit.
With the valve at rest, the two central lands block the flow of fluid across their valleys.
The spring end of the valve is subject to throttle pressure through a circuit connection from the throttle valve and the lower end is subject to modulator pressure acting on the lower face of the bottom land.
A vent between the two uppermost lands prevents hydraulic lock-ups from occurring due to fluid seeping into the valley between them.
In operation, fluid from the pump enters the valve through the orifice and acts against the differential area.
As pump pressure rises, the valve moves upwards against its spring and excess fluid can then pass across the two large valleys to the ports in line with them.
The result is an initial regulation of line pressure to about 450 kilopascals at idling speed.
This line pressure is directed to the manual valve and to the throttle valve at all times,
When "D" is selected, line pressure is also directed to the front clutch, to the 1-2 shift valve and to the governor.
The excess fluid passing across the valleys is directed to the secondary regulating valve and to the converter.
Fluid from the lower port of the primary regulator valve acts on the end face of the secondary regulating valve and raises it against its spring.
The valve movement firstly uncovers a port to the lubrication circuit for the rear end of the gear train and secondly an exhaust port leading back to the pump inlet.
The exhaust bleed off stabilizes fluid pressure in the lubrication and converter circuits to within acceptable limits of approximately 100 to 200 kilopascals.
