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Expansion Vessel Location?


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I am helping a friend fit a calorifier to his boat. It will have a thermostatic mixer valve to blend in cold water to the output so as to prevent scalding. Which side of the mixer should the expansion vessel be plumbed in? Should it be in the hot water pipe from the calorifier, or can it be in the mixed warm water pipe after the mixer valve? On my boat it is in the warm side, after the mixer, but I am wondering if there is anything in the mixer valve that could prevent the expansion vessel from working to stop overpressurisation in the calorifier. The mixer valve will probably be the one that Midland Swindlers sell. Is there anything cheaper/better?

A diagram is attached.

Thanks,  Jenny

 

 

expansion.png

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10 minutes ago, Neil Smith said:

You can get the blender a lot cheaper from tool station or discount plumbers like Mr central heating.

Neil.

Could you provide a link? Google only returns similar or higher prices for me. 

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10 minutes ago, Neil Smith said:

You can get the blender a lot cheaper from tool station or discount plumbers like Mr central heating.

Neil.

Actually, Midland Swindlers is the cheapest I've found so far. A lot less than Toolstation, or Screwfix. I've not looked at Ebay, or the discount plumbers merchants yet, but will be before buying. I've not found the exact model anywhere else yet, but early days. Surprised? Yes I was. Marine usually at least doubles the price!

Jen

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Just now, Jen-in-Wellies said:

Actually, Midland Swindlers is the cheapest I've found so far. A lot less than Toolstation, or Screwfix.

Yep, that's exactly what a couple of minutes Googling showed me. 

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1 hour ago, mickp said:

Surecal recommend fitting after mixer  and my expansion tank is like that.

Any reference for that? 'cos it's not what they say here: http://www.surejust.co.uk/expansion-tanks

"Expansion Tanks are an essential feature on any hot water system. They need to be installed on the hot water supply after the hot water heater. Anywhere on the hot side of the system, but preferably as near to the hot water heater as is reasonably possible. It can be fitted in any orientation."

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I see that if a mixer valve is attached to the tank that the expansion vessel will have to be after it (because there's nowhere to plumb it in prior) as per here: http://www.surejust.co.uk/surecal-vertical-calorifier-connection-instructions but if the mixer valve is remote from the tank then it should be between them. 

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1 hour ago, WotEver said:

I see that if a mixer valve is attached to the tank that the expansion vessel will have to be after it (because there's nowhere to plumb it in prior) as per here: http://www.surejust.co.uk/surecal-vertical-calorifier-connection-instructions but if the mixer valve is remote from the tank then it should be between them. 

That must be right, as the mixer valve also incorporates a couple of one-way valves. (That's also why, if like me you are obsessive about draining pipes in the winter, you need to add some way to drain the "warm" pipes)

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2 hours ago, WotEver said:

Any reference for that? 'cos it's not what they say here: http://www.surejust.co.uk/expansion-tanks

"Expansion Tanks are an essential feature on any hot water system. They need to be installed on the hot water supply after the hot water heater. Anywhere on the hot side of the system, but preferably as near to the hot water heater as is reasonably possible. It can be fitted in any orientation."

Actually, the most sensible and efficient place to fit an expansion vessel is on the cold feed but After the non-return valve, Surecal have a NRV right on the cold inlet so it would need to be removed and fitted upstream which is what I generally do, I guess that’s why they recommend the hot side. Like and accumulator or pressure vessel a certain amount of water is left inside and if it is on the hot side it will cool and be wasted. Not so much of an issue if using an immersion on shore power but if you have made it after a cruise from your engine it’s best conserved by fitting the vessel on the cold side.

Edited by NMEA
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Just now, NMEA said:

Actually, the most sensible and efficient place to fit an expansion vessel is on the cold feed but After the non-return valve, Surecal have a NRV right on the cold inlet so it would need to be removed and fitted downstream...

I totally agree and many diagrams show it there. However it does require modifying the calorifier as supplied which I guess not everyone would be happy to do. Yourself being a professional, you know what you're doing. 

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Whatever you do make sure you fit the vessel in the most inaccessible place on the boat, for example in a corner of the kitchen so you have to virtually dismantle the floor units to get at it.  

Yes, it's a sore point. 

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  • 3 weeks later...

Interesting topic. By the way does anyone know if theres an overboard expansion bleed into the port engine room bilge from either the webasto or calorifier ?  I get a small amount of water in the pocket there after heating water but only in cold weather.

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52 minutes ago, Irob said:

Interesting topic. By the way does anyone know if theres an overboard expansion bleed into the port engine room bilge from either the webasto or calorifier ?  I get a small amount of water in the pocket there after heating water but only in cold weather.

I can not see what type/make of boat this refers to. narrowboats, even mass produced ones tend to be pretty much one offs so without knowing your boat it is all but impossible to say. There shoudl be a pressure relief valve on the calorifier but where it vents to on a particular boat is open to question. It may be overboard, it may be into a bilge, or in one case I found it venting into the gas tank.

I would not expect the Webasto to have this feature because they use an expansion tank.

You need to look into that bilge area to see if you have an open pipe down there. maybe through the bulkhead.

 

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2 hours ago, Tony Brooks said:

I would not expect the Webasto to have this feature because they use an expansion tank.

Depends, many Webasto pro's including me have used closed systems for some time instead of a header tank, in which case there will be a PRV, usually as part of the filling loop / expansion vessel assembly, oranges are not the only fruit.

Edited by NMEA
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32 minutes ago, NMEA said:

Depends, many Webasto pro's including me have used closed systems for some time instead of a header tank, in which case there will be a PRV, usually as part of the filling loop / expansion vessel assembly, oranges are not the only fruit.

I guess it's no different to a land-based unvented water heating system - they must be fitted with a PRV even if installed with an expansion vessel. 

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5 minutes ago, WotEver said:

I guess it's no different to a land-based unvented water heating system - they must be fitted with a PRV even if installed with an expansion vessel. 

 

The main difference is that the design of land-based unvented hot water installations is controlled by law by section G3 of the Building Regulations. 

My guess is there haven't been enough serious incidents in boats yet for the BSS to introduce equivalent regulations for boats.

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7 minutes ago, WotEver said:

I guess it's no different to a land-based unvented water heating system - they must be fitted with a PRV even if installed with an expansion vessel. 

Indeed.

 

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