Expansion vessel

[ACF]

I,m about to install a new expansion vessel (24l) which comes pre pressurised at 4 bar (nitrogen). The shurflo manual says shut-off is 3.1 bar, but can be adjusted. Do I lower the pre-pressure in the expansion vessel or can I raise the shut off pressure on the pump?

[Tracy D'arth]

Can't read all the post as its too wide for the screen!  What did you send it with?

[Tony Brooks]

Lower the pressure in the expansion vessel - make sure it is suitable for potable water and not one for central heating with inhibitor in the water.

[ACF]

Thanks and yes it's potable 

[ditchcrawler]

Is it an expansion vessel to go on the hot water side or an accumulator to go on the cold, somewhere near the pump. They can be physically the same but are set up differently to do different jobs.

[ACF]

It's for the cold water to replace a smaller one that has sprung a leak.

[Tony Brooks]

37 minutes ago, ACF said:

It's for the cold water to replace a smaller one that has sprung a leak.

 

So it is not an expansion vessel, it sounds like an accumulator and they need setting to roughly the pump cut OUT pressure or about half the cut in pressure for maximum effect.

[PeterF]

20 minutes ago, Tony Brooks said:

 

So it is not an expansion vessel, it sounds like an accumulator and they need setting to roughly the pump cut OUT pressure or about half the cut in pressure for maximum effect.

Think you have it backwards as that would be either 3.1bar or 0.75bar rather than the required 1.5bar.

 

They need setting to roughly the pump cut IN pressure or about half the cut OUT pressure for maximum effect.

Edited October 5, 2023 by PeterF

[BEngo]

Yes, definitely set to the pump cut in pressure for greatest benefit.

 

N

[Tony Brooks]

1 hour ago, PeterF said:

Think you have it backwards as that would be either 3.1bar or 0.75bar rather than the required 1.5bar.

 

They need setting to roughly the pump cut IN pressure or about half the cut OUT pressure for maximum effect.

 

True - edited now.

[ACF]

I set it to the cut in pressure and it works perfectly. Thanks for all your help.

[blackrose]

Why such a big accumulator tank? I think mine is only 8 litres.

[Chewbacka]

10 hours ago, blackrose said:

Why such a big accumulator tank? I think mine is only 8 litres.

To run the shower without using the pump?  Additional water storage?  For some, size matters.

[ACF]

12 hours ago, blackrose said:

Why such a big accumulator tank? I think mine is only 8 litres.

There was some unused space and the difference in price is minimal. The pump now only comes on twice a day instead of every time you open the tap. The general understanding seems to be that this is better for the pump and therefore (hopefully) lasts longer.

[ditchcrawler]

20 hours ago, blackrose said:

Why such a big accumulator tank? I think mine is only 8 litres.

In my opinion the bigger the better less times the pump starts and when it does it runs longer 

[blackrose]

15 hours ago, ACF said:

There was some unused space and the difference in price is minimal. The pump now only comes on twice a day instead of every time you open the tap. The general understanding seems to be that this is better for the pump and therefore (hopefully) lasts longer.

 

Ok I see, thanks. By the way, given the volume of your accumulator tank (although this advice goes for any accumulator really), I would definitely fit it with an isolator. It makes identifying if the system has a leak much easier.

 

With my 8l tank I might hear the pump activating for no reason and think nothing of it unless it keeps happening, in which case I can easily isolate the accumulator and instantly listen for a leak. With a 24l tank that leak might never make itself apparent and without an isolator you'll never know about it until you find water in your bilges.

8 hours ago, ditchcrawler said:

In my opinion the bigger the better less times the pump starts and when it does it runs longer 

 

Yes, as long as one has the space for a bigger tank then I agree it's better. Unfortunately bigger tank probably wouldn't fit under my bed.

Edited October 13, 2023 by blackrose