Expansion Tank Size

[Guest ali2992]

What size expansion tank is everyone running? I've seen a few posts in the past mentioning using an aluminium drinks bottle, which I think is a really good idea, but the majority of these are 700ml,which doesn't sound a lot. I've run the math on how much the water *could* theoretically expand and even adding a large margin of error in, a 700ml bottle *should* be enough. Apparently. But I'm still not sold. Thoughts?

[Dave R]

my drinks bottle is fine... assuming you are using the spit it out/suck back when cold cortina method

[Guest ali2992]

Yeah it will be connected to an inline pressure cap and at the highest point

[Jez Morton]

I'm running a Capri expansion tank, not sure of the volume though. I did calculate that 6 litres of water would expand to 6.26 litres at 100°C, when I had an air lock it filled the Capri tank and I Wanted to confirm what the expansion should be.

 

Jez

[Guest ali2992]

Yeah that's what I calculated, added in a few extreme cases too. Withstanding the pressure and temperature is another concern

[maccavvy]

i have a ally bottle off a push bike works a treat

[Guest ali2992]

This may be a silly question, but how do you fill up the system? Because the bottle will be at the highest point of the system, I can't fill up from the inline rad cap?

[Bob Tucker]

seems to be a bit of confusion here.

There are 2 different system used.

1 the rad is pressurised by a sprung cap, with a tube in the filler neck that feeds to an OPEN OVERFLOW bottle.

Any water being spat into the bottle gets sucked back as the rad cools.

 

2. The rad has a simple sealing cap, and a pipe leads from the circulating water system, into a

pressurised EXPANSION tank which has the sprung rad cap.

 

You cant mix & match.

Edited September 11, 2014 by Bob Tucker

[Guest ali2992]

My rad has no cap, I was planning on putting the cap inline along the top hose, the cap will be sat in a T-piece like the ones on Car Builder Solutions where when the pressure on the cap is exceeded the smaller outlet is opened, this will be connected to the expansion tank. So does that need pressurised tank or just overflow tank?

[Bob Tucker]

Hi...if its this one (or similar)

http://www.carbuilde...iller-neck-25mm

 

you need an overflow bottle, lower than the filler neck, not a pressurised expansion tank.

The pipe needs to extend almost to the bottom of the bottle.

 

HTH Bob

Edited September 11, 2014 by Bob Tucker

[Guest ali2992]

Ah thanks for that. So how does the system "suck back" the coolant? Or is it purely a means of saving coolant for future use and not meant to allow the system to self regulate?

Edited September 11, 2014 by ali2992

[Dave R]

as the coolant coos i contracts and sucks back from the drinks bottle.

thats why the tube needs to go to the bottom

Edited September 11, 2014 by Dave R

[sj-bradley]

My first attempt failed to suck the coolant back into the bottle.

 

This was because the raceline water rail did not have a rubber sealing ring in the pressure cap to prevent air getting back into the system. Once I had made this from some spare rubber, it works perfectly.

 

And, from t'internet I find this

-----------

The thermal coefficient of expansion of water is 0.00021 per 1 °C at 20 °C

 

Example - Cubic Expansion of Water

 

100 liters of water is heated from 20^oC to 80^oC. The volumetric expansion of the water can be calculated by using equation 2:

dV = (100 liters) (0.000214 1/ ^oC) ((80 ^oC) - (20 ^oC))

= 1.28 liter

----------------

In other words going from 20 ^oC to 80 ^oCfor 100 litres will give 1.28 litres overflow. So assuming about 5 litres in the system, the expansion should only be 0.064 litres or 64 millilitres.

 

Of course if the coolant boils, it will force more out. The pressure cap is there to increase the internal pressure of the coolant and so elevate the boiling point a few degrees.

 

so, now you know

 

Simon.

Edited September 11, 2014 by Simon B

[Guest ali2992]

Thanks guys, I will have to check my cap to see if it does have a rubber seal. It looks like a 700ml bottle should be adequate then

[ibrooks]

Your cap will need two rubber seals. One is on the sprung part of the cap and is the pressure seal. The second is around the top part of the cap and is what makes any coolant that's been pushed past the pressure seal go along the pipe to the overflow tank. That second seal is also what prevents the system just drawing air back in when it contracts - it makes certain that the only place the system can draw from is the overflow tank and therefore assuming the pipe is in the bottom of the tank it has to draw back the coolant it forced out before it can draw any air.

 

Iain