See Figures 1 and 2
A Crankcase Depression Regulator Valve (CDRV) is used to regulate the flow of crankcase gases back into the engine. This valve is designed to limit vacuum in the crankcase. The gases are drawn from the valve cover through the CDRV and into the intake manifold.
Fresh air enters the engine through the combination filter, check valve, and oil fill cap. This air mixes with blow-by gases and enters the opposite valve cover. These gases pass through a filter on the valve cover and are drawn into the connected tubing.
Intake manifold vacuum acts against a spring loaded diaphragm to control the flow of crankcase gases. Higher vacuum levels pull the diaphragm closer to the top of the outlet tube. This reduces the amount of gases being drawn from the crankcase and decreases vacuum in the crankcase. As intake vacuum decreases, the spring pushes the diaphragm away from the top of the outlet tube allowing more gases into the manifold.
The diesel Crankcase Ventilation System should be cleaned and inspected every 15,000 miles (24,000 km) or at 12 month intervals.
Do not allow solvent to come in contact with the diaphragm of the CDRV, as it will cause diaphragm damage.