GEAR A 1T1641 - Caterpillar

Exhaust Fluid (DEF), also generically referred to as urea, is a liquid that is injected into the exhaust system of engines equipped with Selective Catalytic Reduction (SCR) systems. SCR reduces emissions of nitrogen oxides (NOx) in diesel engine exhaust.In engines equipped with an SCR emissions reduction system, DEF is injected in controlled amounts into the engine exhaust stream. DEF is then transformed chemically into ammonia. The ammonia, in the presence of SCR catalyst, converts NOx into harmless nitrogen (N2) and water (H2O). Refer to Special Publication, SEBU6250, "Caterpillar Machine Fluids Recommendations" or Special Publication, SEBU6251, "Cat Commercial Diesel Engine Fluids Recommendations" for details and requirements of DEF.The cleanliness of DEF is critical to the performance and operation of the SCR aftertreatment system. Contaminants interfere with the controlled injection of DEF and with the SCR system pump performance. Contaminants are introduced into the system mainly during filling of DEF into the engine or machine tank. Dirt at the filling opening (neck) and surrounding area can be introduced into the tank if contamination control precautions are not taken. The surfaces surrounding filler cap should be thoroughly cleaned before opening. The opening of the dispensing container should also be thoroughly cleaned before filling the DEF. These steps help avoid the introduction of contaminants into the system and allow the system to perform as designed.Another source of contamination is dirty DEF. DEF should be clean as the DEF is dispensed into the engine or machine tank. The dispensing container filling neck should be clean and should not introduce contaminants into the DEF engine or machine tank. Caterpillar recommended DEF fill fluid cleanliness is "ISO 18/16/13" as dispensed into the engine or machine tank. Refer to this Special Publication, "Contamination Control"for details.Contamination of DEF can result in poor performance of the SCR system, down time, and increased cost. In order to avoid contamination related issues and downtime, follow all the contamination control guidelines detailed in this Special Publication, "Contamination Control".Note: The cleanliness of the DEF is as important as the cleanliness of the fuel. Caterpillar recommends "ISO 18/16/13" cleanliness level for DEF fluid as dispensed into the engine or machine tank. Refer to this Special Publication, "Contamination Control"for details and guidelines.Multiple filtration steps are designed into the SCR system:Inlet Filtration Screen - There is a filtration screen at the inlet filling opening of the DEF tank. This screen reduces the contamination introduced during filling of DEF engine or machine tank. The screen is a serviceable part and should be changed if the filling time is slowed due to the dirt accumulation or at the published service intervals. Refer to your Operation and Maintenance Manual for information.Header Screen - There is a DEF header screen located in the DEF tank. This screen helps reduce the contamination transported into the system from the tank. For questions about the tank screen, consult your Cat dealer.DEF Filter - The DEF filter is 4 microns absolute efficiency. The DEF is circulated through the pump and then passes through