Quick Question Regarding Vacuum Check Valves
 

I'm trying to understand the basic function a little better. As ya'll know, I installed some Euros earlier. I put in a check valve on the source line going to the vacuum switch. It's supposed to prevent vacuum that's upstream from leaking at the source. Now, in addition to doing that, it's supposed to allow vacuum downstream of it to not leak out either, right? Example, if I have the lights set at position 2, when I shut the car off, the check valve will prevent the lights from going to position 3 (which is the position it falls to when there's no vacuum present) while the car's off, right?