The piston valve sits in the fluid section on top of the ball cage with the dispacement rod, nut, and packings. This will often sit inside of the intake housing or on top of the packing nut.
Part #: 156971
Part #: 248212
Part #: 85.238.155
Part #: 15J743
Part #: 248209
Part #: 193046
Part #: 248206