Having moisture in your air system is the #1 reason you have air system issues.
Volvo Truck Part Number: 85110799
The Air Dryer Cartridge is recommended to be replaced yearly due to being filled with particles that were filtered from the air. This filter will solve your slow build up and will help ensure your air going to tanks is filtered.
Engines: D12 (VED12), D13 (VED13), D16 (VED16), Cummins ISX