See Figures 1 and 2
A Crankcase Depression Regulator Valve (CDRV) is used to regulate (meter) the flow of crankcase gases back into the engine to be burned. the CDRV is designed to limit vacuum in the crankcase as the gases are drawn from the valve covers through the CDRV and into the intake manifold (air crossover).
Fresh air enters the engine through the combination filter, check valve and oil fill cap. The fresh air mixes with blow-by gases and enters both valve covers. The gases pass through a filter installed on the valve covers and are drawn into connecting tubing.
Intake manifold vacuum acts against a spring loaded diaphragm to control the flow of crankcase gases. Higher intake 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 the vacuum level in the crankcase. As the intake vacuum decreases, the spring pushes the diaphragm away from the top of the outlet tube allowing more gases to flow to the intake manifold.