What is the Hot Air Pressure Regulating valve and what's its purpose? What does the hot air pressure regulating valve do, yes I know that it regulates hot air pressure but what does that do, create hot air? How does it regulate hot air pressure? 

I have a picture of the valve here at page 3. It's an Airbus A320 
http://www.smartcockpit.com/docs/A320-Air_Conditioning_and_Pressurization.pdf
The valve regulates the pressure of hot air from the engine bleed system that bypasses the airconditioning packs. This hot air is then fed to the trim air valves to adjust cabin temperature.