Expansion tank query

[mikeonb4c]

Yep..............a question you shouldn't be asking, think jiggle pin............

Mikeob4c will no doubt have some wild theories on why it needs a jiggle pin......

But being serious, there's nothing wrong with wild theories (strictly speaking hypotheses), provided the writer makes it clear they are only theories and asks for comments and corrections. Hypothesis, theory and experimentaiton are the foundation blocks of discovery. It's assumption, over confident assertion and the discouraging of debate that are the enemies of discovery. I probably spend more time on here cross-examining (often to good effect) 'the facts', than I do expounding new theories. The jiggle pin debate is a case in point:

http://www.igmaynard.co.uk/bongo/forum/ ... jiggle+pin

[widdowson2008]

Expansion tank - sawn in half - (ignore red lines - they are mine showing interconnection channels between cells)


Enlarged view of inlet/outlet pipes (circled red in pic 1)

Further enlargement of mystery bit


However, on a closer look, fitted to the outlet pipe (on the inside of the tank) is what looks like some sort of valve. Has anyone any idea as to what this could be? and what it is for?

Mystery solved. I should have listened to TGP earlier (and Ady recently on another thread). Just spent the last 30 minutes carving a tank up. (bloody tough material - some sort of Nylon based material?)
Anyway, as TGP said, its straight through - no fancy valve or jiggle pin type thing. Just straight through at 6mm bore. (Inlet is 13mm bore) So quite boring really . except that it means I don't have to travel that road any longer. QED

One of my problems is that whilst I listen to others, I need to see things for myself. Can be very time consuming and unfruitfull (as in this case)

On the upside, I am now happy to record this as a FACT - no mystery bit - move on.

Still dont know what that was on TGP's, or where it came from

[widdowson2008]

Done these sectional drawings of the expansion tank (accurate dimensionally - not sure about flow arrows, and absolutely no idea how it works - Open to ideas)
TGP tells me this is (or likely is) a degassing/expansion tank. Cant dispute that cos I aint a clue what a degassing tank is (other that a air-bubble-getter-outerer), but I'm more than ready to learn.

For the sake of this excercise, the tank is divided into 2 parts (at the flange)

There are 2 distinct sets of slots in the tank - above the flange and below.

This pic is of the 'above flange' slots, and I reckon their only function is to equalise the (air) pressure in the 9 compartments. Cant see any other purpose, but open to suggestions.


Below flange slots.
If you study them, you will see that some are bigger than others. This is only a suggestion to get the ball rolling, but if you take the narrower slots as being the boundary of a set of cells, then the tank is divided into 3 sets of cells.
1 - Upper left (1 cell)
2 - Lower right (4 cells) Filling section
3 - Lower left (4 cells) Inlet/outlet section
These boundaries happen to coincide with the demakation of the different tank depths that can be seen from the outside.


This pic shows a possible (in fact probable), coolant flow path.
Head down awaiting bullets from those who know what they are talking about.
]

ps - you may have gathered by now that I like drawing pictures

[mikexgough]

Nice and easy to understand diagrams as usual, Steve............ Now......

Degas Tank

Current active deaeration and degassing systems for Automotive cooling systems utilise a coolant bottle having a degassing chamber through which a part of the engine cooling fluid is passed continuously for the purpose of accumulating and separating gas, i.e. air from the coolant.
Such deaeration systems work best when there is a designated air space in the coolant bottle for collection of any air removed from the coolant. Such systems work with high efficiency when the coolant bottle is elevated significantly above the level of coolant in the rest of the cooling system particularly the coolant level in the engine so that any air collected is maintained in the coolant bottle.

However, due to lower bonnet lines in modern automobiles, positioning a coolant deaeration bottle above the level of coolant in the rest of the cooling system circuit is usually impossible.
When the coolant bottle is not located well above the rest of the circuit, air collected in the coolant bottle can back flow into the engine's coolant circuit after operation of the engine is terminated.
Often when collected air is moved out of the coolant bottle it migrates as air bubbles to the vehicle's heater used to warm the vehicle's passenger compartment. These air bubbles may prevent desirable quantities of coolant flow through the heater core, particularly during engine idling. Decreased coolant flow through the heater core prevents the heater system from initially and rapidly warming the cabin of the vehicle.

Accordingly, migration of air bubbles from the heater back to the coolant bottle requires an extended operating time of the Engine including relatively great engine speeds and corresponding water pump speeds. This procedure repeats itself over and over with each engine start-up/termination cycle and has the effect of diminishing effective warming of the vehicle's interior.

read and compare with your system flow diagrams.....

And put another less techie way.....

The degassing tank –

So, how does it work?
Essentially, the beauty lies in the connection circuit diagram.
The entire capacity of coolant is filled in the degassing tank.

The degassing tank is designed and selected in such a way that it defines the topmost point of the entire cooling system including the radiator and the engine.

Essentially if you draw a horizontal imaginary line passing somewhere in the middle of the degassing tank, all cooling system components including the topmost point of the radiator and everything else including the engine must perforce lie below this line.
This is compulsory for the degassing tank to work. So, this defines the mounting location. Now, go to the circuit diagram.

The degassing tank has to have an outlet connection of sufficient diameter, which is connected to the "suction side" of the water pump. Suction side is important.
The first beauty is that when the engine is running, it continuously "sucks" coolant from the degassing tank, so keeping the critical water jackets pressurized with coolant.
It is logical that if coolant has to enter the cooling system, air inside it must be expelled out otherwise coolant will not flow. The second beauty is that this system provides for a passive system bleed.
It is a foregone conclusion that as coolant rises into the cooling system passages, any topmost point in the system must be bled (open to atmosphere). As you can’t just leave it open, it must be reconnected to the topmost point of the degassing tank.
That way when coolant is being filled atmospheric air will be expelled through this orifice and through the open filler cap.
The third beauty is that it is this very bleed which will provide an escape conduit for the cavitation to escape into the degassing tank where it cannot cause any harm.
The fourth beauty is that the degassing tank volume is always decided in such a way that it must be filled partially. Some portion at the top of the degassing tank is the "expansion and cavitation volume").
The fifth beauty is that the filler cap although pressurized does not need two seals, as its outlet to atmosphere is natural. So the pressure cap does not become an overly critical design.

[widdowson2008]

Hi Mike
To a semi-retard like me, that almost makes sense. Unfortunately, I need to do myself yet another sketch to be able to define specific points within the tank that we can all relate to. (I can do naff all without a pic. Sad, but true)
I'll be back

[widdowson2008]

I'm BACK
This sketch identifies each cell so we can define what we are talking about. You'll notice cell volumes have been added (these are accurate)
First of all, we need to define some specific detai because it IS relevant. THE FOLLOWING ARE FACTS:
1 - Cell X has no outlet below normal FULL mark, and therefore the coolant within it ts basically a stagnent reservoir.
2 - Wilst the outgoing pipe (to stat) is 6mm bore, the inner end of it is reduced to 3mm bore. This MUST restrict the flow I would have thought. Bear in mind the ingoing flow pipe is 13mm bore.
3 - The normal FULL mark on the tank is 68mm above the maximum system level.
4 - The LOW mark on the tank is 39mm above the maximum system level.



The least restricted and most direct flow path through the tank is A-B/B1-C.
The only other route through the tank is A-B1-D-E-F-G-C.

Mike - How does this fit in with your post? Not too bad I suspect.

I can only work on numbers I'm afraid, hence all the above nonsense.

[The Great Pretender]

Nice and easy to understand diagrams as usual, Steve............ Now......

Degas Tank


So, how does it work?
Essentially, the beauty lies in the connection circuit diagram.
The entire capacity of coolant is filled in the degassing tank.

It is logical that if coolant has to enter the cooling system, air inside it must be expelled out otherwise coolant will not flow. The second beauty is that this system provides for a passive system bleed.

The theory is correct...............................BUT....................(don't you just love that word) You can't have a passive system with our mid engine.
Once it is relatively free of air the degassing tank will remove micro bubbles in the system. Once air bubbles form in the head IMHO they are trapped there until manually bled.

Steve.......................Widdowson, nice pic but you need to understand how temperature and pressure affect movement.
I asked you about 3 months ago to use your camera to thermal image flow through the tank. You never got back.

[bigdaddycain]

I'm BACK
This sketch identifies each cell so we can define what we are talking about. You'll notice cell volumes have been added (these are accurate)
First of all, we need to define some specific detai because it IS relevant. THE FOLLOWING ARE FACTS:
1 - Cell X has no outlet below normal FULL mark, and therefore the coolant within it ts basically a stagnent reservoir.
2 - Wilst the outgoing pipe (to stat) is 6mm bore, the inner end of it is reduced to 3mm bore. This MUST restrict the flow I would have thought. Bear in mind the ingoing flow pipe is 13mm bore.
3 - The normal FULL mark on the tank is 68mm above the maximum system level.
4 - The LOW mark on the tank is 39mm above the maximum system level.



The least restricted and most direct flow path through the tank is A-B/B1-C.
The only other route through the tank is A-B1-D-E-F-G-C.

Mike - How does this fit in with your post? Not too bad I suspect.

I can only work on numbers I'm afraid, hence all the above nonsense.

Point2: Reduced "bore out" to bigger "bore in" whilst on the surface appears to restrict flow, actually speeds the flow up,cc/flow rate will (i think) be the same as "unrestricted" flow.

[mikexgough]

Nice and easy to understand diagrams as usual, Steve............ Now......

Degas Tank


So, how does it work?
Essentially, the beauty lies in the connection circuit diagram.
The entire capacity of coolant is filled in the degassing tank.

It is logical that if coolant has to enter the cooling system, air inside it must be expelled out otherwise coolant will not flow. The second beauty is that this system provides for a passive system bleed.

The theory is correct...............................BUT....................(don't you just love that word) You can't have a passive system with our mid engine.
Once it is relatively free of air the degassing tank will remove micro bubbles in the system. Once air bubbles form in the head IMHO they are trapped there until manually bled.

Steve.......................Widdowson, nice pic but you need to understand how temperature and pressure affect movement.
I asked you about 3 months ago to use your camera to thermal image flow through the tank. You never got back.

I kind of agree with the usage of "passive" as I think the wording is not 100% for the meaning......and I totally agree with the Air Bubbles in the head are trapped until allowed to be evacuated.....
Now with the MHO engineering Japan Coolant change in mind....where the system and head are vented (after 13 mins engine running and one rev cycle) and then the vent tube (head bleed tube as we know it) plugged......and then after that the engine put through the workshop manual rev/rest cycles......suggests a Degas system where any other smaller amounts of air left in the cooling system are removed the engine "self bleeding" via the Header tank.......and I guess.....

Now put me against the wall if you think I am talking clap trap.....the system will continue to "self bleed" during use (hot/cold cycles/ambient temp changes)........ unless there are other issues (like head gasket failure/water pump leak/hose leaks) that allow more air into the system than the Degas set up can cope with.......
In essence what I am suggesting is..... that they cooling system circuit is "sealed" in normal operation and if any small air pockets occur the trapped air is "burped" ,for want of a better word, in to the Header tank.....BUT if there is more than an air pocket die to a leak somewhere.....then Degas can't cope as per normal operation and so overheats and more occur......if that makes sense..... I'll get my coat

[widdowson2008]

Steve.......................Widdowson, nice pic but you need to understand how temperature and pressure affect movement.
I asked you about 3 months ago to use your camera to thermal image flow through the tank. You never got back.

Hi Mel
You are quite right - you did ask, and I failed to get back - Sorry.
Did actually try, but when looking from above, the camera is trying to look through the 5mm Nylon at the coolant surface, which is 70mm below this. On top of this, the coolant is a permanently moving target and the readings were VERY ambiguous - nothing I would put my name to.
Same applied when looking from the side. Reckon the Nylon material/thickness play a big part in the poor results, or possibly that the temperature difference is small due to constant movement/mixing.

[mikexgough]

I'm BACK
This sketch identifies each cell so we can define what we are talking about. You'll notice cell volumes have been added (these are accurate)
First of all, we need to define some specific detai because it IS relevant. THE FOLLOWING ARE FACTS:
1 - Cell X has no outlet below normal FULL mark, and therefore the coolant within it ts basically a stagnent reservoir.
2 - Wilst the outgoing pipe (to stat) is 6mm bore, the inner end of it is reduced to 3mm bore. This MUST restrict the flow I would have thought. Bear in mind the ingoing flow pipe is 13mm bore.
3 - The normal FULL mark on the tank is 68mm above the maximum system level.
4 - The LOW mark on the tank is 39mm above the maximum system level.



The least restricted and most direct flow path through the tank is A-B/B1-C.
The only other route through the tank is A-B1-D-E-F-G-C.

Mike - How does this fit in with your post? Not too bad I suspect.

I can only work on numbers I'm afraid, hence all the above nonsense.

Steve..... that works fine.....for a Degas set up....... as you can see with the numbers, that it fits with the degas basic principles......and the flow (G,C,B chambers) and looks like that coolant is "compressed into a corner to "jet" for want of a better word towards the outlet - looking at the diagram and the placement of the thermo/heater outlet) is then going to the pumped part of the set up, which I guess that makes the water pump as important as the thermostat in this kind of system.....

I think I need to go away to a darkened room with some hot black cofee and marry the Degas theory in lay terms with the coolant flow/expansion tank diagrams and see what comes out....... whether is is near to a Bongo system or complete claptrap....

[widdowson2008]

Point2: Reduced "bore out" to bigger "bore in" whilst on the surface appears to restrict flow, actually speeds the flow up,cc/flow rate will (i think) be the same as "unrestricted" flow.

Hi bdc
To get an idea of the flow ratio between the 2 pipes (inlet 13mm, and outlet 6mm) I put the tank on the sink with a constant/consistant flow into the filler hole, and noted the flows (see pic)
Pressure is constant throughout the tank (atmospheric). I realise this will be different under true working conditions, but the pressure will remain constant whatever it is, so the pipe volumes will be proportionally the same (dont you think?)
Calculations on the volumes from each pipe indicate that the volume through the 13mm pipe is 5.5 greater than the 6mm pipe, so it looks as if the pipe reduction is restricting flow. Thats what the pic and numbers are telling me, but what do I know?
I cant reconcile these numbers to what you are saying - could you explain please?
Not saying you are wrong - just that I cant fit the numbers/pic to what you are saying. (I'm probably WAYYYYYYYY off beam here.)

[widdowson2008]

.....


The least restricted and most direct flow path through the tank is A-B/B1-C.
The only other route through the tank is A-B1-D-E-F-G-C.

(G,C,B chambers)

I think I need to go away to a darkened room with some hot black cofee and marry the Degas theory in lay terms with the coolant flow/expansion tank diagrams and see what comes out....... whether is is near to a Bongo system or complete claptrap....

Need to get terminology right here Mike - The flow is not G-C-B, its G-C-outlet to stat.
Look forward to results of your meditation session. . Gettin good init?

[The Great Pretender]

Point2: Reduced "bore out" to bigger "bore in" whilst on the surface appears to restrict flow, actually speeds the flow up,cc/flow rate will (i think) be the same as "unrestricted" flow.

I cant reconcile these numbers to what you are saying - could you explain please?
Not saying you are wrong - just that I cant fit the numbers/pic to what you are saying. (I'm probably WAYYYYYYYY off beam here.)

Explanation here.

http://www.scienceclarified.com/everyda ... ciple.html

[widdowson2008]

Explanation here.

http://www.scienceclarified.com/everyda ... ciple.html

Cheers Mel
First scan? some interesting stuff there. Seem to remember something about this guy from college, but probably wasnt paying too much attention at the time.
Logged and printed. Bedtime reading. I'll know all about Bernoulli in the morning.
Question pops up though. I thought the Swiss made cuckoo clocks. Then again, I suppose they had to be mathematicians to do that.