Basically the fuel topping governor acts as a stop for p3/py air. When you exceed the 106% it lets out the p3/py. Without the bellows the fcu is choked off. So the min flow is the governing until you start to get pressure, and the secondaries cut in.
Take two paper coffee cups, "fuel cup" cut a square thru both" metering orifice". Turn opposite, that is the primary governor movement. Lift it up, that is the bellows.
Yes is it simplistic, but explain like your dealing with a 6 year old.
Last edited by rigpiggy; 27th Sep 2017 at 05:19.