Pitot Pressure Circuit.

TM 9-2520-249-34&P

the valve. Pressure at the upper end forces the valve

c. Pitot Pressure Circuit. Figure 2-6 illustrates

down, which rapidly expels oil below the valve through

the effect greater pitot pressure has on the downshift

an orifice.

inhibitor valve and lockup shift valve. The position in

(2) In the valve's downward position, the

which these valves are shown can occur any time pitot

lockup circuit is interrupted and the lockup clutch is

pressure is great enough to overcome the opposing

exhausted through a port uncovered by the valve's

forces.

movement. When the shift is completed and the

(1) Downshift inhibitor valve.

Main-

oncoming clutch has been charged, pressure equalizes

pressure from the high-range signal circuit is directed

at each end of the valve. Due to the larger area at the

between the compensator plugs. Movement of the left

lower end of the valve, the valve moves upward and

plug toward the inhibitor valve compresses a spring

resumes the position illustrated. Lockup operation is

between the plug and the valve. This action assists the

restored when the valve moves upward.

pitot pressure in moving the valve plunger into the

e. Fourth-Gear Signal Circuit. Signal pressure

fourth-gear lug.

in this circuit is directed to the pivot valve. In the

(2) Lockup shift value. Pitot pressure

normal steer position, signal pressure in this circuit is

pushes the valve to the upward position. In this

blocked at the pivot valve. However, when the valve

position, main pressure is allowed to flow through the

rotates (350) to the pivot steer position, signal pressure

flow valve to the lockup clutch. The volume of oil to the

is admitted to the bottom of the steer relay valve. The

converter is reduced to that which can flow through the

steer relay valve is forced upward, and pivot steer is

orifice at the left of the valve. This reduced flow

prevented during travel in fourth gear.

provides adequate lubrication and cooling of the

NOTE

converter during lockup operation.

d. Valve.

The related mechanical functions

(1) The function of the flow valve is to

required for this travel condition are

interrupt engagement of the lockup clutch while shifts

described in paragraph 2-50d, and

are being made. During any shift, except to neutral, the

illustrated in figure 2-18.

oncoming clutch is charged with oil which must pass

through the upper orifice. The pressure differential at

the orifice decreases the pressure at the lower end of

2-20