Header Tank

[deezee]

Right, The coolant header tank I have is utterly unsuitable as its overflow only and not pressurised! Can anyone recommend a simple (ideally square) coolant header tank that has a pressurised cap on it?

Also, does the header tank need an in and an out on it? Or can you just break into a rad hose with a Tee Piece and have it connected that way? The more I look into different manufacturers coolant systems, the more complex they seem.

[gingea1pom]

Deezee,

I am working on radiators and header tanks tomorrow.

My Ford header tank has one outlet of about 15mm at the bottom and one over flow by the cap, if this helps.

Cheers Ginge

[flyerncle]

Audi A4 and the like have a flat oblong header tank with pressure cap and lower outlet and vent pipe at the top,even fitted with level warning.
Not too expensive new.

[deezee]

Where do you plumb the overflow into off the header tank then? I assume you can't just go to atmosphere as its going to stop pressure building and not raise the boiling point.

[gingea1pom]

I think the way it works is the overflow is above the pressure relief bit of the cap.

So the over flow is also were the excess pressure goes.

I think.

Cheers Ginge

[teun]

Take a look here:http://www.emeng.gentlyhosting.co.uk/Cooling/Part1.htm

[deezee]

Great link! Thanks Teun

[teun]

More simple:http://www.toyne.org.uk/docs-cooling.html

[flyerncle]

Exactly what Ginge said,on the Audi tank the cap is the pressure relief valve and it has a channel to vent it out of the bottom of the filler neck.
The reason the system is under pressure is to hold the coolant against the cylinder walls and all the other metal components in the engine to transfer the heat to the water otherwise it would boil away from the metal and no cooling would result and as others have found out the hard way boiling water is not funny under pressure.
The small top pipe on said tank is the return to vent air/water,without it there is no curculation.

[spud69]

I may be wrong Paul but i had always presumed, also, that it was so the operating temperature could be higher when under pressure without boiling, upto 105deg.

Maybe Bull but that's what i had thought.....;)

AndyH

[gingea1pom]

Andy,

You are correct. If you increase the pressure you increase the boiling point.

The opposite is also correct. If you boil a pan of water up on Everest it would boils at a much lower temp than at sea level.

[flyerncle]

And if you add antifreeze/coollant it really bollox's the whole theory ! And the boiling point etc. I will leave thermodynamics to the relavent heating engineer :p