Pistons - Jeep cherokee 2000 Service Manual

21 - 118 AUTOMATIC TRANSMISSION—30RH
DESCRIPTION AND OPERATION (Continued)
NOTE: The accumulator is shown in the inverted
position for illustrative purposes.
Fig. 37 Accumulator in Neutral and Drive Positions
Fig. 38 Accumulator in Second Gear Position
1 – BOTTOM IN BORE
2 – SHUTTLE VALVE

PISTONS

DESCRIPTION
There are several sizes and types of pistons used in
an automatic transmission. Some pistons are used to
apply clutches, while others are used to apply bands.
They all have in common the fact that they are round or
circular in shape, located within a smooth walled cylin-
der, which is closed at one end and converts fluid pres-
sure into mechanical movement. The fluid pressure
exerted on the piston is contained within the system
through the use of piston rings or seals.
OPERATION
The principal which makes this operation possible is
known as Pascal's Law. Pascal's Law can be stated as:
"Pressure on a confined fluid is transmitted equally in
all directions and acts with equal force on equal areas."
PRESSURE
Pressure (Fig. 39) is nothing more than force (lbs.)
divided by area (in or ft.), or force per unit area.
Given a 100 lb. block and an area of 100 sq. in. on
the floor, the pressure exerted by the block is: 100
lbs. 100 in or 1 pound per square inch, or PSI as it is
commonly referred to.
Fig. 39 Force and Pressure Relationship
PRESSURE ON A CONFINED FLUID
Pressure is exerted on a confined fluid (Fig. 40) by
applying a force to some given area in contact with the
fluid. A good example of this is a cylinder filled with
fluid and equipped with a piston that is closely fitted to
the cylinder wall. If a force is applied to the piston,
pressure will be developed in the fluid. Of course, no
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