With neat labeled figure, explain the working of any two position of PCV (positive crank case ventilation) valve.

With neat labeled figure, explain the working of any two position of PCV (positive crank case ventilation) valve.
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1 Answer

Answer :

PCV Valve: It consists of a spring loaded tapered valve for flow control. The crankcase pressure and manifold vacuum act together to close the valve where as the spring pressure tends to keep it open.(Fig a)

At idle and low speed: At idle and low speed, crank case emissions are very less due to lower cylinder pressure and manifold vacuum is high. Therefore only a small flow through PCV would be sufficient to keep the crank case clean. High manifold vacuum at idle and low speed would pull the valve to right to maintain the small flow.(Fig b)

At normal Speed: Blow by increases and manifold vacuum decreases due to which valve moves to left increasing the flow

At high speed or Heavy loads: No manifold vacuum acting on the valve, valve opens to maximum, increasing the flow to maximum capacity. (Fig c)

In case of backfire: During cranking, high pressure will be produced in to the intake manifold which causes valve to back seat sealing the inlet and crankcase is protected from the back fire.(Fig d).

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