[pairodice]

I called Black Label repair and they sent out two guys that seem to know their stuff. Called Newell and spoke to Tanner and he suggested trying to make the coach go up or down in the rear to maybe break something loose and then the valve

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I called Black Label repair and they sent out two guys that seem to know their stuff. Called Newell and spoke to Tanner and he suggested trying to make the coach go up or down in the rear to maybe break something loose and then the air pressure protection valve 
from Grok: air brake system component (pressure protection valve). It protects the primary air system by closing off secondary circuits if pressure drops too low (typically closes around 45 ± 5 PSI). Common in heavy-duty trucks, buses, RVs, and commercial vehicles with air brakes.

•  Ports: Multiple ports (Supply, Delivery, etc.), matching the multi-port cast body in your photo.
•  Cross-reference / Casting: The T-21340-0 and 900328 markings align with OEM castings used on this Bendix valve.

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I called Black Label repair and they sent out two guys that seem to know their stuff. Called Newell and spoke to Tanner and he suggested trying to make the coach go up or down in the rear to maybe break something loose and then the air pressure protection valve 
from Grok: air brake system component (pressure protection valve). It protects the primary air system by closing off secondary circuits if pressure drops too low (typically closes around 45 ± 5 PSI). Common in heavy-duty trucks, buses, RVs, and commercial vehicles with air brakes.

•  Ports: Multiple ports (Supply, Delivery, etc.), matching the multi-port cast body in your photo.
•  Cross-reference / Casting: The T-21340-0 and 900328 markings align with OEM castings used on this Bendix valve.