By combining its Diesel Oxidation Catalyst (DOC) muffler and Spiracle closed-crankcase ventilation (CCV) filtration system, the company has found a way to reduce both tailpipe and engine-crankcase emissions in medium- and heavy-duty trucks. With DOC, users see benefits such as enhanced catalyst performance, uniform airflow and temperatures, and reduced exhaust backpressure. The Spiracle filtration system includes a replaceable filter, pressure-relief valve, and a bottom-drain oil-sump connection to return coalesced oil to the engine. A top-load design provides easy serviceability. The filter change-out is designed to coincide with the engine manufacturer's oil-change-interval requirements. These two systems meet the EPA's Voluntary Retrofit Program warranty requirements and are available individually.