PCV valve

[EngJW]

Hello,

I have a project to add closed crankcase ventilation to an old industrial engine. I want to use automotive components. Here are my questions:

1. How to determine what size pcv valve to use. Is there data anywhere? Or should I just select one from a similar displacement engine?

2. Can anyone post a link where I can find dimensional data and pictures of styles, or even a catalog? My searches over the internet have been unsuccessful.

3. Anyone know of what crankcase pressure shold result from a correct design?

Thanks,
John Woodward

 

[werdnaid]

I don't know if engine size makes a whole lot of difference. In the 60s Chevys 6, SB8, & BB8 all used the same one. What would make a difference is amount of blowby & speeds engine is run.

I suspect that a industrial engine would run at a fairly constant & loaded speed. Instead of a standard PCV valve, that pulls at vacuum into the intake manifold & the crankcase is vented to atmoshere, you may want something similiar to what Porsche has used on some of their turbo motors. This is a sealed crankcase, except for a vent to a separator trap & return which has another line running to the air cleaner for vapor evacuation.

drew

 

[EngJW]

This is an L-head V4 engine. What we are thinking of doing is pulling in fresh air from the air cleaning into a closed oil filler cap, and then pulling the vapors out of the valve chamber. We probably would need a baffle to prevent drawing in oil. We may have to add a restrictor orifice in the line if the pcv pulls too much vacuum in the crankcase. Not only do we not want to suck oil out of the crankcase, we do not want so much vacuum that dirt is drawn in through the crankshaft seals.

However, I am confused by some of the explanations, or maybe my understanding of a pcv valve is all wrong. According to what literature I have been able to find, the valve is nearly closed at high vacuum when blowby is low. At high speed, when the vacuum goes away, the valve opens fully to draw blowby into the intake manifold. It is only if there is more blowby than the valve can handle that it enters the intake through the air filter. I also think that drawing in blowby through the air filter leads to deposits around the throttle plate.

Please enlighten me if I am wrong.

Thanks,
John Woodward

 

[mrmopartech]

John,I do not think a PCV valve will work on your motor,as to for it to work,there has to be a variation in the rpm and vacumn to open and close the valve.If the motor stays at a constant rpm,there will be no use for the valve,as it will be closed all the time.Using a vent system to the carb with a small K&N air filter could be a way to solve the problem.If you are getting blow by in the motor,it needs to be re-ringed to stop it,no PCV valve will help at all.Now I have seen vent tanks on motors,where a tube dumps the excess fumes ito a pickup tank with a screen.If you can tell us the rpm that the motor runs at most of the time and the cubes we may be able to desin some thing for you,scott

 

[EngJW]

Scott,

This engine spends a lot of time at full throttle, but it does get some time at part load and idle. It is an EPA requirement that we add closed crankcase ventilation. The certification and endurance test have a significant amount of time at part load.

This engine at one time had a pcv valve for a specific application. I think a lot of the splash oil was being sucked up through the hoses. I will try a baffle at the opening. We are going to use throttle body EFI so I would think that we would not want to expose it to blowby. It seems that with a pcv valve this engine should work just like an automotive engine at full throttle.

John Woodward

 

[strokersix]

"According to what literature I have been able to find, the valve is nearly closed at high vacuum when blowby is low. At high speed, when the vacuum goes away, the valve opens fully to draw blowby into the intake manifold. It is only if there is more blowby than the valve can handle that it enters the intake through the air filter."

John, Your above description of PCV operation exactly matches my observations in practice. You may want to consider the physical orientation of the PCV valve. It seems to me that the valve might be sensitive to gravity so if the valve was upright in the original application you probably want you application to mount it upright as well.

Mike

 

[werdnaid]

John,

Check this, Purolator # AS-802 or Porsche # 931-107-221-01. It is vented from the crankcase on a Porsche 924 turbo or 931, drains back to the crankcase, and pulls crankcase pressure to the lower pressure in the air breather housing. The connection on the air breather housing is upstream of the air filter element, CIS or K Jetronic flap for the fuel distributor and throttle body on Bosch injection.

The 3 connections on this part are about 7/8 hose. The more air the motor takes in, the more blowby that is pulled out of the motor. I imagine that this could be used to pull from the valve cover. There are no other vents on this motor except for the turbocharger lubrication, the crankcase is sealed. If you connect upstream of the air filer element, you should get no more buildup on your throttle body butterfly than a normal PCV system & you would have a lot less crankcase pressure during the high load full throttle runs.

Drew

 

[mrmopartech]

John,with that imfo I would agree that it will work just like a regular auomotive system.And the addition of EFI,it will reduce the amount of gas that will reach the crankcase,by running at a perfect air/fuel ratio.Now you can flip over a number of valve covers from dodge ,ford,gm and others to see a hundred different ways to make a baffle,and even ones that work witha passage way with metal screen to stop oil being drawn into the line in its raw forum.My biggest concern was I did not know what rpm that it would sit at for long periods of time and if it would very at all to operate the PCV valve system.I would go with some simple groments in the valve covers and a simple PCV,with 3/8 tubing to try a set up and test it.This amount of parts might come to 30$ if you get the right PCV valve from a chev or some other make,and a simple drilling and taping of a hole in the intake manifold.Most speed shops sell after market groments for the valve covers to install vents and PCV,check it out and right back what you found,scott

 

[franzh]

John:
There are two basic types of PCV systems:
1) Active, which uses manifold vacuum to create a vacuum in the crankcase;
2) Passive, which uses no vacuum, but allows crankcase vapors to enter the air cleaner assembly.
I have used the second method several times to pull crankcase vapors from the crankcase, just installing a simple tube from the crankcase between the air filter and the inlet port. There is a slight vacuum present, maybe 1 to 3" wc, enough to pull vapors. This works great on large displaement engines. If this is a diesel engine and there is quite a bit of blowby, the vapor in the inlet can actually change the power curve by supplying oil mist fuel.
Franz