frequency valve operation? crank holding tool?

[Nicholas Lawrence]

    Can someone explain the operation of the frequency valve, not so much as
what the ECU does with it but specifically what the three vac lines do,  and
why on a 10V motor both wastegate ports are plumbed and only one on the 20V.
I understand applying pressure to the diaphragm keeps the waste gate closed.
    On the tool that holds the crank from turning when removing/installing
vibration damper pulley, what does it stop against to prevent the crank from
turning?
    Respond to me if this something not everyone would want to hear.
    TIA
    Nick    nick at beol.net