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Thread: ? Negative pressure on 300tdi PCV

  1. 23rd June 2007, 05:17 PM #1
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    ? Negative pressure on 300tdi PCV

    Righteo, I have all but plumbed my air conditioner to air compressor system. High pressure side is simple, but Im happy. I bought an inline oiler with view to rig it on the intake line... but... inline oilers dont like low pressure suction, thems are built for high pressure, also it is quite restrictive.

    So, option one is to have a main filtered airline into the compressor with a side air line with oiler on it, will of course work but will also be untidy?

    Someone mentioned on the earlier thread to plumb the intake off the PCV that way you get filtered air with a dose of crankcase oil. Initially I didnt love this idea as I thought the negative pressure under the rocker cover could cause seal dramas. But have just spent some time in the engine bay. If one was to t-junction off the top PCV hose, the air will draw from the rocker cover but as air pressure (like politicians) always takes the path of least resistance, any excess negative pressure will be drawn from the much larger air filter to turbo ducting, thus limiting negative pressure in the crankcase. My theory sounds too good to be true - does anyone disagree with my thoughts? Or should I just run with it and see!!!

    - and yes it will be a very neat install if I do it this way!

    regards
    Steve
    '95 130 dual cab fender (gone to a better universe)
    '10 130 dual cab fender (getting to know it's neurons)
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  2. 23rd June 2007, 05:50 PM #2
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    only one thing wrong with this approach...

    the PCV should have a guard and a spongy filter between it and the rocker cover whose purpose in life is to stop oil from getting drawn into the air inlet side of the engine which on a diesel has the potential to cause a run-away...

    if thats all in place and working correctly your not going to get much oil to the compressor.

    Id be fitting an inline oiler set up as a venturi feed like a degreasing gun on a seperate line and then hiding the hosing as best you can back to the airfilter box. then fit a auto ejector valve on the bottom of a tpiece set up to act as an oil trap and have that return to the inline oiler resivior. Use a good compressor oil vent the top of the resivoir and keep it as close to the exhaust as you can manage so that the heat will drive moitsture out of the oil.
    Last edited by Blknight.aus; 23rd June 2007 at 05:55 PM.
    Dave

    "In a Landrover the other vehicle is your crumple zone."

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  3. 23rd June 2007, 05:57 PM #3
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    Very good then, I thought it too good to be true.

    The biggest hassle with the oiler on a seperate line is that all junctions are t-pieces and thus it is hard to keep all pipes in line. I will sort something I am sure.

    Steve
    '95 130 dual cab fender (gone to a better universe)
    '10 130 dual cab fender (getting to know it's neurons)
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  4. 23rd June 2007, 06:05 PM #4
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    what about an oil separator in the discharge line plumbed back to the sump or suction line ?

    My old Javac refrigerant recovery unit uses a Sanden compressor and has one of these to stop the compressor losing it's oil.
    It looks as simple as a cylinder with in and out tubes and a capillary tube going back to the compressor, and for all I know it may be as simple as this. Larger refrigeration systems use a cylinder with some sort of impediment to oil flow, often two gauze screen socks on the inlet and outlet that make the oil fall out of the flow by impingement, and a float in the base of the cylinder that opens and allows the oil to flow back to the compressor.
    A similar arrangement, without the float in the bottom and just a reasonable bore capillary would work. The one on my reco unit is less than 3" tall.

    Maybe contact http://www.javac.com.au/ to find out if you can get one ?
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  5. 23rd June 2007, 06:08 PM #5
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    I dont see how its a problem... set up your LP line or suction line to the compressor thusly

    filter, airbox, line-oiler venturi-line-compressore inlet

    setup the hp line thusly

    compressor out- line- oil trap- tpiece- uphill side to main resivoir downhill side to auto eject valve

    from the vent of the ejector valve plumb back to the resivior that feeds the oiler venturi. its neat its simple and it works really well. The biggest hassle is keeping water out of the oil
    Dave

    "In a Landrover the other vehicle is your crumple zone."

    For spelling call Rogets, for mechanicing call me.

    Fozzy, 2.25D SIII Ex DCA Ute
    Tdi autoManual d1 (gave it to the Mupion)
    Archaeoptersix 1990 6x6 dual cab(This things staying)


    If you've benefited from one or more of my posts please remember, your taxes paid for my skill sets, I'm just trying to make sure you get your monies worth.
    If you think you're in front on the deal, pay it forwards.
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  6. 23rd June 2007, 06:15 PM #6
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    An oil return/seperator is the best way to go.

    You have two choices

    Manual - just fit a standard oil reciever/seperator, from a small ac system (which is basically a small sealed can) with a pipe and a manual tap going from the bottom of the 'can' to the sump or suction side.

    Or automatic

    Use the same set up - but with a solenoid valve wired through a simple timer which operates at startup of the compressor.

    Have the solenoid open for 2 - 3 mins every time the compressor is run, and any oil is then sucked back into the sump from the oil receiver/seperator.

    Okay you will have to wait 2- 3 mins before the compressor will produce full power, but this way you are pretty sure you are lubricating the compressor.

    Oh by the way - don't use PAG, or POE compressor oils - they are hygroscopic and will emulsify. just use standard mineral compressor oil (suniso 3 or 4 gs comes to mind) or a PAO oil like erg1000

    These are virtally non hygroscopic
    Last edited by ladas; 23rd June 2007 at 06:19 PM.
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