Fitting an Expansion Vessel

11 Apr 2007
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United Kingdom

We are having a potable water expansion vessel fitted to our Megaflo unvented hot water cylinder so as to avoid having to go through the process of re-forming the air bubble every 6 months.

Our plumber is certified to work on unvented hot water systems.

Due to congestion in the cupboard, where the tank is located, there will be approximately 0.5m of 22mm copper pipe running along horizontally and then approximately 1m of 22mm copper pipe rising up vertically to the bottom of the expansion vessel. The expansion vessel will be fitted to the wall.

What I was wondering, and what the plumber was not sure about, was will the vertical section of pipe, going up to the vessel, ever fill with water due to trapped air ?

If this is the case will the vessel still absorb any expansion due to the water being heated ?

The top of the expansion vessel will be below the water level in the Megaflo tank.

Many thanks in advance.
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I had to buy the parts and will have to squeeze into the cupboard - the plumber said he will sign it off for me if I do all the awkward work.
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Should we aim to keep the distance from the water flow path to the expansion vessel to the minimum to reduce the amount of trapped air or will the vessel still work i.e. the trapped air will push against the bladder inside the expansion vessel when the water begins to heat up ?

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