From Wikipedia, the free encyclopedia
 
 The Positive Crankcase Ventilation System (PCV) is a one way passage for the blow-by gases to escape in a controlled manner from the crankcase of an internal combustion engine.

The blow-by gases are generated when a small but continual amount of gases (air, unburned fuel, combustion gases) leak from the combustion chamber past the piston rings (that is, blow by them) - and the piston ring gaps - to end up inside the crankcase, causing pressure to build up in there. Additional sources of blow-by that contribute to this effect are gases leaking past the turbocharger shaft, the air compressors (if present) and in some cases the valve stem seals. The blow-by gases, if not ventilated, can condense and combine with the oil vapor present in the crankcase forming sludge or cause the oil to become diluted with unburned fuel, degrading its quality and decreasing its effective life. Additionally, excessive crankcase pressure can lead to engine oil leaks past the crankshaft seals and other engine seals and gaskets. Prolonged period of oil leaks can starve the engine of oil and damage it in a permanent way. Therefore, it becomes imperative that a Crankcase Ventilation System is used. This allows the blow-by gases, consisting of the combustion products and the oil vapors, to be vented through a PCV (positive crankcase ventilation) valve out of the crankcase. There are three system architectures when the blow-by gas exits the crankcase. It can either enter the air inlet manifold (Closed CVS), be vented freely in the atmosphere (Open CVS) or be vented in the atmosphere through a filter (Filtered Open CVS).

Volvo/Ford ST225 PCV

 The Volvo/ FORD ST pcv system  is made out of two parts like most cars.

There is high vacuum /low throttle side, and then wide open side ,Low vacuum high positive pressure side and its a complete closed system.

Now lets look at the high vacuum side

During this state oil vapor inside the engine is sucked into the intake manifold through the oil filter housing which is open to the bottom of the cylinder block and connected to the cam cover.

Inside the OFH you will find a diaphragm which regulates the flow as the vacume pull is rather strong, strong enough to suck in the oil seals on the cams and the crank , causing them to leak.

This particular diaphragm also act as a shutof valve when the car is in boost, but helped by the little reed vavles situated inside the manifold runner gasket.

Now the WOT/High positive pressure side

Under wide open throttle the vacume in the intake manifold turns to positive pressure. Now the little reed valves gets blown againt their seats to close the system from the pressureto make sure no pressure gets past them and pushes on the diaphragm and all is well.

In turn there is still alot of vapor pressure and positive pressure inside the block that must go  somewhere, this is where the secondary system kicks in

Volvo utilizes an anti pollution regulating valve at the turbo, now this is connected at the throught of the turbo which under boost will suck on this valve which is connected via the lower manifold to the cylinder block, oil vapour gets pulled into the high pressure air stream pushed through the intercooler and piping and the burnt inside the combustion chamber

And all is well! 

BUT 

Thats where the problem stems off.

So in the past we focussed on the Boost / high pressure side  

Some boost leaked past the reed valves, causing pressure on the Diaphragm located in the OFH, causing it to rupture.

End result was usually a high pitch scream at idle.

Our fix at the time was a swing action one way valve with an enclosed catch can.

It worked, saving numerous diaphragms in its stride  

BUT

then we found more and more Tuned cars with a smoking habit!

Now where do we start......

So we started looking at the low pressure / vacuum side 

For some reason oil mist must be suck  or blown into the combustion chamber.

We tried venting the pressure side . Which didnt help as the car would suck in un measured air and would run lean under vacuum............................................

 

 

ST180 occ

ST180 OCC for enclosed box

ST250 OCC

St225 Oil control can