Accumulator - again!

[fezster]

I've read all past posts on accumulators and wanted to gauge what advantage there was to choosing an off the shelf product such as coldstream or mainsboost, compared to a Reliance 500l potable expansion vessel which has a replaceable membrane.

Is there any fundamental design difference which allows the off the shelf product to have a longer life, or is it all marketing?

I'm also assuming that any of these would work in practice identically as long as they are installed and setup correctly by a competent person.

 

[Dan Robinson]

Coldstream and mainsboost are totally different.

Coldstream and a normal expansion vessel are different on terms of build quality, and apparently, there is a diffuser inside to help ensure no stagnation of water.


What whether that justifies the price I don't know.

We either use a Provess unit or a cheaper "copy" depending on application and budget.

 

[fezster]

Thanks Dan.

I was comparing the GAH Coldstream to the TWS MainsBoost:

http://www.gah.co.uk/heating/coldstream/technical-specification.php

http://www.stuart-turner.co.uk/products/mainsboost/mainsboost/


They seemed to be essentially a large expansion vessel with a schrader valve and various controls on the incoming pipework. The diffuser you mentioned is why I am considering these more expensive products, because if it lasts longer/is more reliable, then it may be worth the extra investment.

If you don't mind me asking - the units you've fitted, have they been in operation long, and have you had to replace any because of ruptured membranes?

 

[Dan Robinson]

None of the units I've fitted have had problems when serviced annually.

Apologies though, I was confusing your mainsboost with the Provess.

The the TWS and the Stuart Turner 7 units are the same AFAIK.

 

[fezster]

Looking at ChrisR's post from the now infamous thread 10 years ago:

Using Precharge = lowest dynamic pressure,
Vessel volume V and
Static Mains pressure M, (all pressures as measured on gauge)
Stored volume is given by V(1 - (P+1)/(M+1))

Read more: https://www.diynot.com/diy/threads/poor-pressure-on-a-megaflo.51701/page-8#post-376543

I'm trying to work out what my usable volume will be on, say, a 500l cylinder. Using this equation, on the recommended 3.5 bar mains, 2 bar precharge, I'm getting approximately 166 litres. Reading all of the literature on the various big brand accumulator websites, I'm assuming the actual usable capacity is 500 - 166 = 333 litres (approx 66%). I'm asking because I'm partly intrigued on how this works and because I want to ensure I choose an appropriate vessel size.

I also wanted to know whether this volume is usable in full? Again, reading past posts, they describe the initial draw off being at the max pressure available and then slowly decreasing as the accumulator runs out. Is there a percentage at which the accumulator doesn't add any benefit, despite still holding water?

And one other concept I'm struggling with - at 3.5 bar mains and 2 bar precharge (the recommended setting according to GAH and TWS), the accumulator is supplementing the mains dynamic pressure. Does that mean whichever is the highest of mains or accumulator, that's the dynamic pressure you will be getting? Is it therefore advantageous to have a higher precharge, if your mains is capable of a higher static pressure. Just wondering why 3.5/2 is the "recommended" setting from GAH and TWS?