Lift Pumps: Remove Air : HOW?

[brods]

Never heard that air can’t dissolve before. The lubrication industry certainly thinks so. Here is a link to just one of many: Machinery Lubrication Magazine

Dissolved Air



Dissolved air is not easily drawn out of solution. It can be a problem when temperatures increase quickly or pressures drop. Petroleum oils can contain as much as 12 percent dissolved air. When a system starts up or when it overheats, this air changes from a dissolved phase into small bubbles. If the bubbles are less than one millimeter in diameter, they remain suspended in the liquid phase of the oil, particularly in high-viscosity oils, causing air entrainment, which is characterized as a small amount of air in the form of extremely small bubbles dispersed throughout the bulk of the oil.

I learned about dissolved air relating to cutting/grinding oils and would hate to think that myself and most everyone else is misguided on this. Is your source saying that no gasses can really dissolve or just air can’t, or just air in petroleum products? Please ask your source, by his definition of entrained, if as the air bubbles get more and more minuscule there is a point where the "entrained" air will behave like it was dissolved rather than being made up of discrete bubbles. Is he just splitting hairs?



I find the distinction important for understanding air separation. If the air is dissolved then it will flow right through a filter and some other means for its elimination are necessary.

 

[CEkstam]

If you nail an engineer or scientist down on the subject they will wiggle a little but will eventually admit it. I have only talked to two actual scientists in my life.



Now when we start talking about pulling high end distillates out of solution, that's another subject. This is the reason it is advisable not to exceed 12" hg on the inlet side of a pump. Vapor develops. The retarding of the injection at the 1,200 to 1,500 rpm range and the nose dive of the torque that is common with class 8 trucks is caused by this. Detroit recommends not to exceed 12" hg with a dirty primary filter. Most all of the class 8 engine manufacturers recommend changing the primary filter at about that vacuum level.



Thanks,

Charlie

 

[Gary - K7GLD]

If you nail an engineer or scientist down on the subject they will wiggle a little but will eventually admit it. I have only talked to two actual scientists in my life.



Now when we start talking about pulling high end distillates out of solution, that's another subject. This is the reason it is advisable not to exceed 12" hg on the inlet side of a pump. Vapor develops. The retarding of the injection at the 1,200 to 1,500 rpm range and the nose dive of the torque that is common with class 8 trucks is caused by this. Detroit recommends not to exceed 12" hg with a dirty primary filter. Most all of the class 8 engine manufacturers recommend changing the primary filter at about that vacuum level.



Thanks,

Charlie

All that is fine in a diesel fuel system that relies upon SUCKING it's fuel thru the fuel filter, then on to the Injection Pump and engine - and that is also the method used in the pointers supplied earlier to point up and explain the entrance of air/vapor into the systems USING that setup, as well as the claimed need to then add air separation devices - but OUR trucks do not use that type system!



In our OEM setup, the LP is sucking from the tank thru an open line, with no internal obstructions (NO filter!) other the the inlet screen inside the tank - and if THAT becomes a clogged restriction, the "fix" to to correct the issue with that screen by cleaning or replacement.



This is why I have a bit of an issue with those earlier pointers - they base their basic testing premise and conditions upon a situation that does NOT apply to our trucks!



The remaining question is, especially for those of who have relocated the OEM LP down close to the fuel tank so it pushes instead of sucking, is how MUCH remaining tendency is there to agitate or otherwise generate vaporization of fuel in the lines, over and above whatever is already present in the primary fuel supply (fuel tank)?



And for THAT, we need some form of test data that applies directly to our trucks, and our specific systems - not tractors, earthmoving equipment or other setups that might be far different than ours! Conditions that apply to a large Caterpillar construction earthmover might be FAR different than what our trucks are likely to be exposed to - and using/quoting comments or testing used on those might easily be quite irrelevant as they apply to us...

 

[CEkstam]

Hi Gary,

Something to think about. Pumps do not suck fuel in. As a pump begins to operate, it creates a place for liquid to go. If the liquid has a positive pressure to drive it in will flow into the pump and then the pump will push it out to where ever the port goes. The force to drive the liquid into the pump is atmospheric pressure plus the column weight of the liquid if the pump is below the surface and minus the weight of the column of liquid if the pump is above the level of the liquid. Again, the flow of liquid into the pump is restricted by the size of the pump inlet and atmospheric pressure. About atmospheric pressure, you will loose about 15% atmospheric pressure at Denver (5,280ft) and 30% at 10,000ft. That is why diesels loose power at higher altitudes. As you drive through the mountains and loose atmospheric pressure, the vacuum at the inlet to the pump increases (even pumps mounted in the tank), vapor is formed through pump cavitation and timing becomes retarded in unit injection systems, rotary or inline injection systems with injector lines, but not common rail systems. Common rail systems will probably just loose rail pressure. So, as most people think that a vacuum is a force by itself when it is really just a measurement of pressure differential to the negative side of ambient, we have also been led to believe that air can become dissolved in a liquid. Remember when our ancestors thought the world was flat. Nothing wrong with this, its just that we know better today, we learn as we go.



Not trying to be a smart acre, just pointing out how some things just slip by.



Thanks,

Charlie

 

[Gary - K7GLD]

Hi Gary,

Something to think about. Pumps do not suck fuel in. As a pump begins to operate, it creates a place for liquid to go.

YUP - agreed - just trying to keep it in easy to understand layman's terms!

 

[FLynes]

Gary & Charlie,



What an interesting thread! Just a thought here, Gary, but I was thinking about your 5 gal bucket test. If the level of diesel did not decrease, is it possible that the air is suspended in the diesel and can not escape, due to the viscosity of the diesel? Also, what happens when you fill the diesel in a bottle to the top, instead of halfway, cap it and shake?



Thanks again to both of you for the food for thought.



Just an aside to Charlie, I finally found a place to do the install on my truck, but they're backed up until the New Year. They primarily do big trucks; they are a certified Freightliner/Cummins repair shop, but they said they'd work on mine, which I thought was damn decent of them.

 

[MA2LA]

Ok this has been pretty well beaten so i wount even get in to the debate except for this, by far most who buy these systems are buying them for the incressed filtration and fuel suply and could care if it truely does its little air trick.

 

[Bob4x4]

This is the reason it is advisable not to exceed 12" hg on the inlet side of a pump. Vapor develops. The retarding of the injection at the 1,200 to 1,500 rpm range and the nose dive of the torque that is common with class 8 trucks is caused by this. Detroit recommends not to exceed 12" hg with a dirty primary filter. Most all of the class 8 engine manufacturers recommend changing the primary filter at about that vacuum level.



Thanks,

Charlie

The Cummins spec for the 24 valve is 6"hg per TSB 14 002 02 rev a



Bob

 

[Gary - K7GLD]

I would think that spec would be more appropriate and critical as provided by the injection pump maker (Bosch, in this case) than by the engine maker...



Naturally, they each have their own eggs to fry... :-laf