| Let's call the little vacuum barb: "the barb". Boost
pressure there goes above the diaphragm (trying to hold it shut).
Let's call the big hole on the bottom where the boost enters: "the inlet". Pressure there goes against only PART of the diaphragm from below (trying to open it). Let's call the tiny little hole next to it: "the little hole" Pressure there goes below the diaphragm, and pushes on the ENTIRE diaphragm (trying to open it much harder than the inlet tries). The Talon BOV lifts off the seat at 20-21 psi when pressure is blown ONLY into the inlet, with no air pressure/vacuum present at the barb or at the little hole. The boost at the inlet is pushing against about one square inch, so it needs lots of psi to lift it against the stout spring. The Talon valve lifts off the seat at 20-21 psi when equal pressure is blown into the inlet AND the little hole AND the barb, because the pressure below the diaphragm (little hole) and above the diaphragm cancel each other out, and once again the boost can only push against one square inch. The Talon valve will NOT lift off the seat at all, with boost pressure going to the main feed tube, and to the barb, but NOT to the little hole. Now the boost is pushing against one square inch under the diaphragm, but against many square inches above it; the top will always win, and the valve will stay closed. Hence my invention to disable the little hole's feed only during high boost, or only when floored. The Talon valve will lift off the seat WAAAY before 21 psi when boost goes to the inlet and to the little hole, but not to the barb. As you lift the throttle the boost begins to drop rapidly, but *BEFORE* it can actually reach "zero", the many square inches of diaphragm that are being hit by boost from below (with nearly NO boost still above it) will BLOW OPEN!! That prevents the developing pressure spike from developing! ;) The Talon valve will open even faster with boost to the inlet and the little hole, but with vacuum to the barb. This is the situation when it is set up for the "fast reacting" mode talked about elsewhere, and the throttle blade suddenly closed while boosting. (You lifted throttle suddenly.) The closed throttle blade creates vacuum in the intake manifold, which is ported to the barb, while both the inlet and the little hole have the boost 'trapped' in the intercooler tubing lifting the diaphragm. The Talon valve will often LIFT OFF THE SEAT while I am cruising up a hill at 1 to 2 psi of boost. I can hear it hissing out, and when I flip my toggle switch to vent the little hole to atmosphere, it *instantly* slams shut and stops hissing. I can flip the "hiss" off and on like a light with my switch. :) It lifts while only in 2 psi of boost, because the
intercooler tubing has somewhat more boost in the intercooler tubing
while you only have 2 psi of boost in the intake. (I measured 6-10 psi
in Mini's tubing) Since the boost is pushing against ALL of the bottom
of the diaphragm at once, 6 psi pushing on several square inches
is just more forceful than 2 psi pushing on one square inch.
|
Note that the BOV above is shown "bottom up" to be able to see all parts, and also that it has been modified with a short tube epoxied to the "inlet" and with a small nylon barb added to the "little hole." |