Crankcase ventilation systems
Crankcase ventilation systems
(OP)
Hi everyone! I have some questions about crankcase vent systems with pcv valves.

there is one system

there is another system

and there is pcv valve
My question is, when and how fresh air from intake before throttle plate could flow INTO crankcase? Like in second picture. If at idle pcv highly restricts air coming from crankcase, then pressure in crankcase should be less than atmospheric to draw air from intake before throttle plate via breather tube.
If engine running at WOT, then pcv also closes, because pressure after throttle plate is about atmospheric and all blow-by gases should go out via breather tube, which is before throttle plate, but only if crankcase has higher pressure than atmospheric. (Or via pcv, if crankcase pressure eovercome pcv spring force).
So pcv is open only at mid engine load (like in 3rd pic) and then in crankcase maybe is slightly vacuum, and in that situation can be, that air comes IN crankcase from breather tube which is before throttle plate (like in 2nd pic)? OR all system should work like in first picture, when fresh air never comes into crankcase? Or maybe i don't understand something?

there is one system

there is another system

and there is pcv valve
My question is, when and how fresh air from intake before throttle plate could flow INTO crankcase? Like in second picture. If at idle pcv highly restricts air coming from crankcase, then pressure in crankcase should be less than atmospheric to draw air from intake before throttle plate via breather tube.
If engine running at WOT, then pcv also closes, because pressure after throttle plate is about atmospheric and all blow-by gases should go out via breather tube, which is before throttle plate, but only if crankcase has higher pressure than atmospheric. (Or via pcv, if crankcase pressure eovercome pcv spring force).
So pcv is open only at mid engine load (like in 3rd pic) and then in crankcase maybe is slightly vacuum, and in that situation can be, that air comes IN crankcase from breather tube which is before throttle plate (like in 2nd pic)? OR all system should work like in first picture, when fresh air never comes into crankcase? Or maybe i don't understand something?





RE: Crankcase ventilation systems
Passenger car engines need ventilation. That is, at one remote region fresh (clean) air comes in that has to migrate thru all sections of the crankcase, cylinder head etc and then go into the intake to be burned.
Just venting off pressure ( no fresh air inlet ) would leave stagnant regions.
At full throttle WOT the PCV valve is wide opent I believe.
http://www.aa1car.com/library/pcv.htm
RE: Crankcase ventilation systems
Yes, i was wrong, at WOT pcv valve should be open, sorry, it closes only when manifold pressure overcomes spring force (turbocharger or backfire). So air comes into crankcase via breather only then, when crankcase has lower pressure than intake before throttle plate, and crankcase has lower pressure than intake before throttle plate only at mid engine loads? Because at idle, pcv is closed, and at WOT, pressure through all intake system is about atmospheric, so vacuum in crankcase can not be, or i'm wrong? And at WOT all blow-by gases should go into intake via pcv and also via breather, yes?
RE: Crankcase ventilation systems
I believe when the PCV is "closed" at idle it still is a small calibrated leak which lets "air" ( plus blowby ) into the carb.
There is still blowby at idle, so if unvented, there would be pressure in the crankcase. There is ( or should be) vacuum in the crankcase at idle because the PCV uses the high manifold vacuum.
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
This description at the autozone sight is pretty specific for Isuzu engines , gas, diesel and turbo diese types. It appears for neither diesel there is no "fresh air in".
==================
This discussion over on a Dodge truck Cummins news group discusses a
http://www.cumminsforum.com/forum/07-5-09-3rd-gen-...
These are supposedly quotes from Cummins service manuals. They suggest that at high loads the unthrottled air intake does still have enough pressure drop to require regulation/limitation by the CDR, but there is no mention of "fresh air" into the crankcase.
I don't picture diesel blowby being daisy fresh so as to not benefit from a fresh air intake, but I guess that may be the case.
"The CCV valve is used to vent crankcase gases back into intake of engine. If crankcase ventilation filter becomes clogged, under high intake vacuum situations, the CCV will prevent the engine from siphoning crankcase gases and oil from the engine crankcase."
"The CDR, Crankcase Depression Regulator, is designed to function with low-level vacuum. The tuna-can size is to accomodate the large silicone rubber\synthetic diaphragm. Vacuum on the diaphragm actuates the valve against a low-pressure spring, calibrated for turbo or non-turbo applications, which also functions to ensure that the valve opens as vacuum decreases.
Fully open at idle, it will begin to close as power demand and vacuum increases, regulating the 'depression' in the crankcase such that excessive oil is not drawn out of the engine, and blow-by pressure in the crankcase does not increase."
====================
Some diesels have intake throttles, presumably to create some manifold for EGR or something.
Look at the complicated centrifugal oil vapor filter and heateres used on some Mercedes diesels
http://www.jeepforum.com/forum/f67/jeep-om642-crd-...
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
I have a '59 Chevrolet Apache truck where the previous owner replaced the 6-cylinder with a 305 V8. I noticed when driving at high rpm (highway driving) oil accumulates on top of the engine at the junction of the valve cover/head and the intake manifold. One pcv port on the passenger valve cover was blocked, so I inserted new pcv valve and ported it to the air cleaner. The driver side valve cover has pcv valve ported directed to intake manifold.
Anyone have any suggestions as to why oil pools on top of intake at the valleys with the heads? Only other thing I could think of is blow-by past the valve cover gaskets. Perhaps blow-by or gassing between the intake and heads pushing oil up and through intake manifold gasket. There is no vent from the oil pan or lower end of the block.
I welcome your thoughts.
BMobile
RE: Crankcase ventilation systems
... but the engine in the vehicle now is not that old, so you can't do it the 1959 way.
... which by the way, did allow/cause oil pooling on the engine, but only hot rodders cared, hence the vents.
Try to figure out the age of the current engine, and try to approximate the PCV plumbing for a vehicle of that era.
Mike Halloran
Pembroke Pines, FL, USA
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
"One pcv port on the passenger valve cover was blocked, so I inserted new pcv valve and ported it to the air cleaner. The driver side valve cover has pcv valve ported directed to intake manifold."
No, if the PCV valve is on the driver side, the passenger side valve cover should be connected to the air cleaner WITHOUT a PCV valve.
RE: Crankcase ventilation systems
The oil is likely from some bad valve cover gaskets, they really didn't do a very good job with the amount and spacing of the bolts to help them seal.
RE: Crankcase ventilation systems
[img http://workshop-manuals.com/ford/Mondeo_2007.5_02....]
it has same crank vent system like in this picture, all info of that vent system i can find is:
"The PCV system consists of a crankcase vent oil separator connected to the crankcase and valve cover by hoses.
The crankcase pressure is controlled by a diaphragm operated PCV valve built into the valve cover and cannot be removed. As the pressure in the crankcase vent oil separator reduces, the diaphragm valve closes against the force of the PCV valve spring, so closing the PCV valve. As the crankcase pressure rises, the PCV valve is pushed open assisted by the PCV valve spring. This allows the positive crankcase gasses to be scavenged by the air intake system."
So, on the right side is oil separator which is connected to the head and to the crankcase, in the head is pcv valve, and in other side of head is hose, which connects head with engine intake system (not shown in this picture). To hose, which connects oil separator and crankcase, is connected another hose (left one), which goes to engine head, maybe someone knows that hose (left one) purpose?
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
Also, you have to recall that any explanation in a workshop manual could be misleading or wrong.
Jay Maechtlen
http://www.laserpubs.com/techcomm
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
Piston rings, like o-rings, rely on the pressurized fluid enhancing and even creating their seal. The sealing relies on the difference in pressure.
IN the extreme if the pressure wer equal on both sides there would be no seal.
At TDC the inertia of the top compression ring can overcome the compression pressure and cause ring flutter etc.
Current thinking is the second ring gap should be larger than the top, specifically to be sure the pressure between the rings is as low as possible to enhance seal.
Here is one discussion -
http://speedtalk.com/forum/viewtopic.php?f=1&t...
RE: Crankcase ventilation systems
But how that pressure difference affects rings sealing? It helps reduce rings flutter and keep rings on the bottom of the ring groove? I heard, that if there is enough vacuum in crankcase, it's posible to use lower tension rings and get less friction from them
Source: http://nutterracingengines.com/racing_oil_pumps/cr...
RE: Crankcase ventilation systems
je suis charlie
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
RE: Crankcase ventilation systems
That's what the key word Positive in PCV means.