Need Help With Air Leak

[Alan-MCI5A]

Our bus has been sitting awhile and when I started it, I heard a leak just behind the front wheels.  I have attached a picture showing the component that is leaking.  The leak is coming from the smaller unit in front.  It is on the passenger side and is located next to the air tank.  It has a plastic cap and stopped leaking after I gave it a tap and got its attention.  Thanks for the help....Alan

[Sammy]

It's called a pressure protection valve. Check the air schematic for your bus to determine the correct rating of this valve.
Some are 60psi,85 psi and 100 psi. i have also seen them set at 20 psi. they all look the same, but are not.
Good luck with your repair.
Sammy 

[Alan-MCI5A]

Thank you Sammy.  I will dive deeper into the manual.

Alan