Basically you have one check ball at the vapor vent (which is in the pump plunger head), one above which is the pump discharge ball (held by the spring and T shaped device--that one is 3/16" diameter and not aluminum) and a third in the power valve (already mentioned). That's pretty much it for balls and if you get a proper rebuilding kit they should be included. When you force the pump plunger downward, the vapor check ball is seated (it goes upward to seat). The pressure of the fuel traveling through the discharge passage pushes up on the pump discharge check ball and allows fuel to pass by it, on through and into the boost venturi part. Usually the ball in the pump head is down. In the down position any vapor in the pump well will go past that ball, into the float bowl and from there out the vent in the air horn.
The two springs used on the pump are calibrated and I'd say both are important...especially the duration spring but also the return spring as they do work together. Hope this helps. Good luck.
