If you have the valve cap I am thinking of, then These type valve caps that shows a pressure or lack there of, press down on the spring loaded valve core, thus keeping it open.
If you unscrew the cap about 3 rotations very quickly, the spring should snap the valve core back shut, sealing it off.
If it doesn't then, the core may be bent.
Being in the tire business, I hate these kind of valve caps. They cause a lot of leaks.
If Wolf Pup is trying to say this is a pressure monitoring system in their sales literature.........
A pic would greatly help so I can see exactly what you have., to see if it is something similar to this.