grazzledazzle
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| posted on 20/1/09 at 04:08 PM |
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more expansion tank q's
My cooling system runs without a header tank. I have a filler neck in the top hose with a pressure cap with a valve and a vent presumably to deal with
pressure relief and expansion. Do I run a pipe from this outlet to an expansion tank? If so is this effectively just an overflow tank? Any links to
something suitable? Do I need the tank plumbing in anywhere else in the system too?
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coozer
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| posted on 20/1/09 at 04:16 PM |
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Tank is normally plumbed into the bottom hose and the vent you've got goes to the top breather on the expansion tank.
1972 V8 Jago
1980 Z750
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grazzledazzle
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| posted on 20/1/09 at 04:38 PM |
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What I don't understand though is if I run a tank to the bottom hose the system will no longer be pressurized as the header tank can't
have a pressure cap on aswell as the other cap? I thought there was a difference in running a header tank and an expansion tank. I also believed you
could run without either?
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daviep
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| posted on 20/1/09 at 06:11 PM |
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Yes an expansion tank is effectively and overflow tank. No it doesn't need to be plumbed in any where else apart from the connection on the
filler neck. The bottle should be open to atmosphere and should have enough coolant in it to cover the hose from filler neck to ensure that air is not
drawn in to the cololing system as it cools down.
Coozer is talking about a header tank which is part of the cooling system and has a constant flow of coolant through it at all times.
You need one or the othe or you risk drawing air in to the system.
Davie
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grazzledazzle
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| posted on 20/1/09 at 06:22 PM |
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Good man, just what i thought.
Next question does it matter at what height this goes relative to everything else in the system?
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contaminated
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| posted on 20/1/09 at 07:08 PM |
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No. It will pull coolant back in under a vacuum as required and there is no issue with air locks because it's not part of the actual cooling
system. Use an anodised drinks bottle like me. Wilkinsons do some nice ones and you can even use a bike bracket to hold it if you want.
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grazzledazzle
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 posted on 20/1/09 at 07:32 PM |
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cheers
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NS Dev
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| posted on 21/1/09 at 01:34 PM |
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worth putting a touch of science around this one as it seems to come up again and again and few seem to understand what's going on!
First the fact that causes the issue - water expands as it gets hotter!!
next, it needs some room to expand. No room and it will make some though the weakest joint!
The pressure cap is that weakest joint.
With an overflow system, the main pipework up to the pressure cap is "full" of water. As it heats up, it expands, the pressure rises very
rapidly and water is forced out of the pressure cap into the explansion tank via a pipe (that needs to be fully to the bottom of the tank). As the
temperature falls the expelled water is drawn back in via the immersed pipe.
With a header tank system (MUCH better in my opinion) there is a vessel (doesn't have to have flow through it at all) within the system that
contains a fixed volume of air at ambient temperature. As the water in the system heats up, it expands, and because unlike water, the air is (easily)
compressible, it gets compressed and makes room for the water. The pressure cap then only opens once the air is compressed up to the opening pressure
of the cap.
As long as the air volume is sufficient to accomodate the water expansion, the system will be fine.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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