Oil Bath Vs Dry Filters

[Scott Crosby]

I worked on a bus this spring that the paper filter didn't do better.  They had a filter minder gauge on it and it was in the green.   I opened the housing and.... no filter.   The owner said oh I forgot I put that in my other bus like two years ago and forgot to order a new one for this bus....  I suppose he could have removed an oil bath filter too or forgot to put oil in it because that kind of stupid is real stupid

[brmax]

I started putting these turbo pre cleaners on dirt and gravel equipment way back because sometimes in a fleet way ya try to stay ahead and its tough sometimes.
http://www.turboprecleaner.com/
I used the 1 and followed up when they introduced the II model, they help tremendously.
Its been (I don't know why) but will just say bean counting, even though I'm a stickler for measure up accountable, anyway in enough meetings and training the mention not to touch the dry air cleaners now, to say blow it out (as old days)because it introduces dirt? whatever.
The promoting in many instruction sessions is that the sensors and gauge sometimes in cab both mechanical and commonly now dash warnings for air restriction, kinda the new thing.
The inspection is a great thing for sure, measure up or get your lunch box and hit the road that's the way it was when I was hired, now its have some cookies
I guess many things are making it not only easier as this air filtering but in ways providing a proof its ok and keep working, ah? don't know, anyway! ( do you remember the first time you got a message on the truck dash screen ) wha  
My utility tractor outside still has oil type filter, even while sand blasting it 15 years ago to repaint I musta thought 100 times if only there was a decent fit for replacement.
It had crud just 2 days ago "before this post" and I wished the same again.
Something important and just mentioned by John, In old and especially many new aero type hoods on trucks sometimes filtering out wet and snow can be a real task, ya know this when they start freezing up and restricted if not fitted with diversion air from say engine area, big pita and cold way out in the boonies at 2am.

Floyd

[bevans6]

Clifford has a good memory, the PO ran the engine in my bus with no oil in the filters for who knows how long, there was a half inch of dust sludge inside the air box when I looked inside.  Done and dusted, I changed the engine.

Point of trivia I guess, oil bath air filters work by forcing the air through a 180 degree change in direction directly over the oil bath.  The high velocity of that change in direction literally flings the dirt particles out of the air stream at the oil surface, which captures the dirt.  The air then passes into a large volume of steel mesh that is damp with oil, and smaller particles stick to the oil on the mesh.  The design works based on Bernoulli's principle, believe it or not.   Small area of air passage towards the oil cup creates high velocity to effectively fling the air, then large volume of space with the steel mesh slows the air down so dust can be captured by the sticky oil.  This is why there are typically three or four oil bath filters - they depend on the ratio of size for their operation, so they can only be so big for a given volume of air.  To get the required air flow they put more filters in parallel.

One thing no one ever discusses is air flow restriction and it's effect on performance.  A restrictive air intake system kills performance exactly the same as a restrictive exhaust.  I don't have any data on this, but I would expect that the oil bath filters are far more restrictive than a big Donaldson.

Brian

[luvrbus]

I found this in bulletin 39 page 2 from Detroit

"Dry type air cleaners are the most efficient cleaners available for mobile equipment.They can separate up to 99.8 to 99.9% of the dust from the air at acceptable pressure looses.The efficiency of dry type air cleaners remains constant over a range of engine speeds."     

[Runcutter]

When I was on a management team that took over a transit fleet, we found that previous (parsimonious) management had instructed maintenance to blow out the paper filters, not replace them.  Fleet of 100 Fishbowls.  I think the older group (45) had oil bath, I do know the newer (55) had paper.  We lost a lot of engines -- and our machine shop was painfully slow at overhauling.

Same property, previous management.  The Maintenance Department had used it's budgeted allotment of Freon (5 tanks for 100 buses in a mid-Atlantic state), so the crafty Maintenance Manager submitted a purchase order for chlorodifluoromethane, which was approved.  Unfortunately, the invoice came in marked "Freon", so he got in trouble.

Arthur

[TomC]

All you have to do is look at the giant mining trucks and that they have multiple dry air cleaners. When I turbo'd my 8V-71, I changed the air cleaner from a 6" to 7" intake and supply. The case was the same, but the element is conical. To add supply, I added another air intake. Dry air filter elements are relatively cheap. Do not blow out elements-the air pressure can create micro holes in the element allowing dirt in-just buy a new element. I like Donaldson. Good Luck, TomC

[dtcerrato]

Question on the restriction mentioned about oil bath cleaners. Would the restriction have as much a negative effect/performance deficit on a super charged engine as on a non supercharged engine?

[bevans6]

Restriction always has the same effect.  It's a resistance to the flow of air, and it varies with velocity and volume of air.  With a supercharger or a turbocharger a designer can overcome the initial effects of resistance, and make it so they can be effectively ignored, by doing things like waste-gates - which allow a booster to produce a certain level of boost, and any excess is thrown away.

In the case of a two-stroke DD engine, the boost is mechanically fixed and there is no over-boost reduction, so any resistance will have an effect.  The blower grabs chunks of air and forces them into the air box, the blower grabs more air than would be there normally, and so there is a pressure buildup inside the air box, and the cylinders are pressurized.  If there is an intake restriction the effect would be that air pressure at the inlet of the blower is reduced below atmospheric, so the chunks of air the blower grabs are smaller and the pressure inside the air box is less.  The engine is getting somewhat less air than it might otherwise, so less power can be produced.  If nothing else is changed and the restriction is great enough, you might get black smoke or need to reduce the size of the injectors.  This is exactly the same effect as you see if you drive your engine at a high altitude - the pressure at the inlet of the blower is lower, the chunks of air are smaller, the performance is less.  Is this going to happen with the oil bath air filter on your 1950's bus?  Almost certainly not, because the bus engine was designed as a system with that exact air filter in mind.  Would reducing restriction help performance and economy?  Absolutely yes, but to what degree I have no idea.  I just know from decades of experience building race engines that it will help. 

Oil bath air filters are, in my humble opinion, fine.  They are state of the 1930's art.  They are serviceable in the field, they can be designed to match the engine in terms of flow, they aren't bad.  A three or four chamber oil bath air filter setup, exactly what I had in my bus, if I was to try to buy a new one today would cost between $1,000 and $2,000.  It was over 100 lbs of intricate stamped steel, lots of fabrication, captive nuts, bolts, clips, it was complicated.  I replaced it with a $100 Donaldson that weighs 15 lbs, is 1/4 the size and has 2015 state of the art filtration.