ping ed sirret (expansion vessels)

[TMC]

Hi

Further to my previous post

My boiler is on the first floor

I can fit the expansion vessel at the side of the cupboard with the boiler in and box it in, in which case I would want the water connection at the bottom

I could fit the vessel near to the ceiling in the room below (a utility room) in which case it would be about 400mm below the boiler and I would need the water connection at the top

are there any issues with either location or which way up the vessel is?

I assume that as my boiler has its own pressure gauge all that I need is a connector for the vessel some copper pipe and a T into the existing pipework

My boiler is 18kw output running 8 rads 3 doubles (1 at 6' x 2' 1 at 5' x

2' 1 at 3' x 2'6" ) 5 singles all 2' high (6', 5', 4', and 2 at 2')

I am assuming from the faq that an 8 litre vessel would be enough

cheers

Tony

[dennis]

AFAIK it doesn't matter. There shouldn't be any air in the water side of a pre-charged (they should have pressurised air in before you fill the system)vessel so there shouldn't be a problem bleeding it either (i.e. you don't).

Do you know how big the one in the boiler was?

[Andrew Gabriel]

I don't think so. Mine (part of the boiler) has the entry on the side.

A number of boiler installation instructions say it should be T'ed into the pipework near to the pump inlet. I presume this is so the pump sees it's smoothing effect on sudden changes to system pressure (such as when a valve closes), i.e. it acts also as a shock arrester.

If you've got a long run from the vessel to the T, I was thinking to myself if it was worth increasing the pipe diameter to reduce resistance, but then I thought that would increase inertia of the water inbetween, which would reduce the effectiveness of the shock arrester aspect, so I didn't come to any conclusion here.

In the case of a significant vertical run with the vessel higher than the T, I would think about adding a manual bleeding point. Otherwise the vessel will fill with air from the pipe. That doesn't matter from the operational point of view of the vessel, but when the system cools, some of this air could get blown back into the pipework, which would make bleeding the system a pain (would take a few heating and cooling cycles before it stopped pushing air back into the system).

[TMC]

I have not had time yet to any dismantling to get to the pressure valve to test

I am having second thoughts about the cause of the problem however

The symptoms are

The system shows just under 1 bar when cold when the heating comes on it goes up to almost 2.5 bar and gradually drops back to 1.2 bar whilst the system is running. only a few drops of water are lost from the prv. I am sure that it did not rise anywhere near to this previously, nor do I understand why it drops back without having dumped lots of water.

If I add water to the system when cold to 1.2 bar (where it had been set for many years) when it heats up it goes over 2.5bar and dumps maybe 1/2 pint to a pint of water out of the prv. When cold the pressure is back to 1bar

any ideas appreciated

Tony

[TMC]

Thanks for this

If alongside the pipe run will be about 300mm horizontally from the flow outlet of the boiler, if on the floor below will be about 400mm horizontally and 300mm vertical drop so no problems there but seen my other post re second thoughts about the cause

Tony

[Ed Sirett]

Sounds like the tube going to the Expansion vessel may be nearly blocked.

[Ed Sirett]

It also makes sure the system pressure is between Vessel & Vessel+pump rather than Vessel-pump and vessel. The pump is typically 0.3-0.5bar.

[<me9]

The replacement one I fitted recently said it had to be fitted vertically (bottom entry). I put it on the wall close to the boiler, teed into the return pipe.