When replacing a Norgren you obviously need to do a leak check on the fittings. But I have learned that I can save myself a lot of grief if I bench check the new valve before I install it.

I just used a bunch of fittings that I could thread into the new valve on my workbench and apply air pressure at the various points to verify the new valve will work and is leak free. Should the new valve have even a minor leak it drives you crazy trying to sort out why the bus leans or loses air, especially when all the fittings on the bus to the valve are leak free. If you are just replacing one valve it is less frustrating because you can zero in on that one valve, but if you are changing out all the valves at once it eliminates the risk of having to figure out why the bus with new valves is still leaning or losing air.

As to keeping the air system dry, that is a little bit of preventive maintenance that pays huge dividends. The cost to change dryer elements every year or two (I use two year intervals) and to drain all the tanks every time you get under the coach keeps the inside of the Norgrens clean, shiny and dry and eliminates many problems due to moisture. I know of at least two coach owners whose poor air system maintenance resulted in a Norgren having a hydraulic lock which makes diagnosis of any problem much more difficult.