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Header Tanks / Expansion Tank Plumbing


speedtripledan
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Ive spent hrs reading on the internet and am getting a little confused, i want to add some form of expansion system to my engine, it will need to be pressurised as the temps are siting close to 100deg etc, how do i plumb a one of these systems to my engine,

 

My rad has a 10mm outlet at the top (blanked off) the retro ford water rail has a bypass out let (blanked off) and i,m using an inline filler neck with 16lb cap in the top hose. with over pressure outlet, this is plumbed to a gbs tank with inlet to base of tank and out let to atmosphere

 

how would i plumb a tank into this setup whilst keeping it under pressure..

 

cheers

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The expansion tank is nothing more than exactly that - a tank that's large enough to allow expansion of the system under pressure. Just put it high up - it needs to be above the highest waterline of the rest of the system - above the head, above the rad, etc.

 

The take-off on top of the rad is usually nothing more than a very useful bleed so that any air trapped in the top of the rad can escape into the expansion tank. No significant amount of water normally passes through it, is my understanding/observation.

 

The over-pressure outlet on your pressure cap, I'm not sure why you're running it to a catch tank, just dump any excess straight out of the engine bay via a small tube. What you ideally want is your pressure cap on your header tank, and the header tank is then filled to low/half-way, allowing enough head of air to allow for pressure build up and expansion in the system without the water trying to blow out of you pressure cap.

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My pressurised expansion tank vents to a catch tank. If any water expands out of it it gets sucked back in as the water cools when engine is switched off. The expansion tank vent pipe goes down to the bottom of the catch tank

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Purpose of the Pressure Cap

When the pressure inside the cooling system increases above its psi rating, the pressure cap releases some of the coolant into the overflow tank. It does this by use of a spring loaded valve. Once enough coolant has exited the system to reduce the pressure, the valve closes again. This action allows the system to remain at the optimal psi while the engine is running. This is great for when the engine is running, but what happens when you turn it off?

As the engine cools down and the pressure in the system drops, the pressure cap allows the excess coolant in the overflow tank to return to the system by use of a second spring loaded valve. This second valve responds to the vacuum created in the system from the drop in pressure and pulls the coolant out of the overflow tank. Not only does this recycle the excess coolant to prevent air pockets in the radiator, but it also prevents the softer components of the cooling system, such as the hoses, from becoming crushed by the external air pressure

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I would agree with Brumster. It is just a pressurised vessel in your cooling system at the highest point.

 

Pretty much every modern car is this setup so pop the bonnet on your tintop and have a look is one option.

 

As long as the pressure vessel has a pressure releasing cap then the radiator shouldn't really have a pressure releasing cap. I guess if you can't get a non valved cap i guess just getting a much higher poundage one than the pressure releasing cap on the expansion tank will do, as the expansion tank will in theory always vent first then.

 

I cant see the need for a catch tank as no modern car has this. You just have a plastic pressure tank with a cap.

 

 

Just to add as far as i am aware both spit/suck and an inline expansion tank are both pressurised systems. The spit/suck one just doesn't have a pressurised expansion vessel, the cap has valves for both direction so once 13lbs (or 16lbs or whatever you have) etc is reached it will vent to the expansion tank and any trapped air bubbles out and when it cools negative pressure opens another valve and pulls water back in if needed. A pressurised vessel has air in it so it just pressurises the air and the water level just rises and falls a bit, i assume there must be a 2 way valve as well so air can be pushed out when pressure is reached and pulled in when it drops. I think 13lbs raises the boiling point to about 110degrees from memory (could be wrong) so 16lbs will be higher again. The higher the pressure the more problems you will have with keeping the water in. So if you can improve cooling and run a lower poundage it will be better.

 

hth

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Purpose of the Pressure Cap

When the pressure inside the cooling system increases above its psi rating, the pressure cap releases some of the coolant into the overflow tank. It does this by use of a spring loaded valve. Once enough coolant has exited the system to reduce the pressure, the valve closes again. This action allows the system to remain at the optimal psi while the engine is running. This is great for when the engine is running, but what happens when you turn it off?

As the engine cools down and the pressure in the system drops, the pressure cap allows the excess coolant in the overflow tank to return to the system by use of a second spring loaded valve. This second valve responds to the vacuum created in the system from the drop in pressure and pulls the coolant out of the overflow tank. Not only does this recycle the excess coolant to prevent air pockets in the radiator, but it also prevents the softer components of the cooling system, such as the hoses, from becoming crushed by the external air pressure

 

Well you learn something every day; I never knew it worked the other way!

 

edit: I will just say, I've never seen one of these in practise - an expansion tank that vents into another overflow/catch tank just seems utterly pointless. A sealed system with a pressure cap, to an overflow, fair enough. But the expansion tank approach does away with the need IMHO.

Edited by brumster
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Dan, sounds to me that at the moment you are running a traditional old style with an overflow pipe from your pressurised filler cap going to a non-pressurised expansion tank

To go to a more modern style system with a pressurised header tank I would look at getting a tank from VW group car, a Renault Clio or a rover 25. They usually have one large diameter outlet which you need to T into your bottom hose and one small diameter inlet which you can connect to the 10mm outlet of your rad, or maybe the one from the water rail or the one currently feeding your expansion tank. Some header tanks have more than one small inlet so you could use more than one of these pipes as in many modern systems. You'll need to swap your current pressure cap for a blank cap and have the pressure cap on the header tank.

The header tank needs to be the highest part of the system to allow the system to self bleed the air out and should have enough space above the max mark to allow the water in the system to expand when fully up to temp without overflowing. Water should only come past the pressure cap if you have over filled the system or you've cooked the engine and it's boiling over.

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Guest lotusPaul

My elan and i expect many other 60s cars runs a spit n suck as described above. Its fine for fast road and trackdays without overheating.

 

If im reading it right you have simmilar. By adding an expansion tank, pressured or not, it will only serve as a reservoir for the expanding coolant.

So in theory you will have less coolant in the system to cool the engine. Counter productive.

Im thinking that there are other issues present that need to be rectified, or i fear the fault will not be fixed, just covered up.

 

So, hows your waterpump flowing? Is it running the correct direction for the installation? Are you instruments and senders compatible and getting correct voltage?

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When my temps were down at 80 or so there was less expansion, now I'm running in the 90,s there is obviously more expansion. I want some where for the expansion to go then return. Stockport Steve has hit the nail on the head in how he describes it or at the very least it's what I thought and wanted confirmation of
As far as pump direction and gauges the pump is ewp and there are 3 temp sensors all reading the same.
Being heavily modified and running almost double the bhp Henry ford intended means the engine is potentially generating a lot more heat.
I.m trying to create the car for every occasion b road blasting cruising on a large tour or track days, cruising it runs cooler than thrashing and i want my cooling to handle both extremes without the need to pop the bonnet every time I go out.
Thanks for all your input it's all valuable

Edited by DanE
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If you are running without an expansion tank of any type now, you will have an air gap at the top of the system. In "normal" cars this would be in the top of the Rad the highest point in the system, that may not be the highest point on a kit.

 

Expansion systems prevents an air gap within a cooling system. The non pressurised allows expansion into a container that is drawn back into the system when it cools, the container can be fitted virtually anywhere. The pressurised system just keeps the air gap in the expansion tank, the reason it must be at the highest point of the cooling system.

 

Neither have any great effect on cooling of a "normal" car, although with a kit the air gap is removed from the main part of the cooling system which will improve its efficiency. Although you could argue there is generally a greater volume of water in a pressurised system, it is the efficiency of the circulation and radiator that maintains temperature. The weakness of the non pressurised system is that it uses atmospheric pressure to force the coolant back into the cooling system, so the system pressure valve to container must be able to take vacuum. The pressure type require it to be at the highest point of the system.

 

Must cut answer short, back to work :-)

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