Accumulator and PRV question

[Johnny80]

Can someone confirm my understanding of pressure vessels is correct?

A PV is supposed to operate at mains pressure. The instructions state that it must be pressurised to 1.5 bar under mains pressure.

You also have to fit a PRV rated at 3.5 bar infront of the PV.

So would the pressure in the PV have to be set at 2 bar? How does then provide mains pressure? Is it the sum of the output at the PRV plus pressure in vessel (3.5bar+2bar)?

 

[Newboy]

Not quite sure what you're fitting but the phase 'G3 ticket' springs to mind!

The function of the expansion (pressure) vessel in an unvented system to provide expansion space - water expands when heated and is non-compressible. The air within the expansion vessel is compressible and allows expansion & contraction of the system fluids. Without an expansion vessel, the system would over-pressure as soon as it got hot.

 

[Johnny80]

I was thinking more in terms of accumulators. Not fitting one - just trying to understand the science behind them.

If the incoming mains is 6 bar, and the PRV reduces it to 3.5 bar, and the pressure in the accumulator is recommended to be 1.5 less, then the max pressure in the accumulator would be 5.5 bar which is under the mains pressure of 6 bar

Just trying to understand how it all balances out

 

[Newboy]

I have no idea what your figures are meant to mean - none of them add up!

1.5 bar less than 3.5 bar is 2 bar
1.5 bar less than 6.0 bar is 4.5 bar

Where do you get 5.5 bar from?

 

[Johnny80]

Output at PRV is 3.5 bar
Pressure in accumulator is 1.5bar less (so 3.5bar - 1.5 = 2 bar)

3.5bar (output at prv) + 2bar (pressure in accumulator) = 5.5bar

So the 5.5bar must be static pressure I guess. When multiple taps are turned on, it must maintain dynamic pressure at static pressure rate I'm guessing

 

[Dan Robinson]

3.5bar plus 2bar = 3.5 bar.

 

[Johnny80]

3.5bar plus 2bar = 3.5 bar.

Ah, so the pressure in the accumulator will always match the maximum of the PRV at best, and if below PRV maximum, the mains pressure?

 

[simond]

Yep. But the pressure drops as soon as a draw off is made.

There was a massive thread on here some years ago when I had the temerity to suggest an accumulator to resolve someone's poor water flow, and a lot of the resident 'experts' tried to pull me to bits. I think it got to over 20 pages, I was like a lone voice in the wilderness. Some of them are now recommending accumulators on this very forum having quietly forgotten how loudly they shouted that they couldn't work - even though the Romans invented them.

Present company excepted, by the way.

PS: If I sound a bit bitter, it's because I am.

 

[Agile]

For an accumulator to work well it needs a high mains static pressure as well as a careful design.

But it also needs users who understand that it only provides a limited higher rate flow for just a few minutes. Then it will take a while to recharge, sometimes 10-15 minutes!

Saw a useful application of an accumulator to provide drinking water from 30m length of 3 mm tube!

Tony

 

[Dan Robinson]

Yep. But the pressure drops as soon as a draw off is made.

There was a massive thread on here some years ago when I had the temerity to suggest an accumulator to resolve someone's poor water flow, and a lot of the resident 'experts' tried to pull me to bits. I think it got to over 20 pages, I was like a lone voice in the wilderness. Some of them are now recommending accumulators on this very forum having quietly forgotten how loudly they shouted that they couldn't work - even though the Romans invented them.

Present company excepted, by the way.

PS: If I sound a bit bitter, it's because I am.

Vaguely remember that one. DDon'tthink I was a naysayers. Seem to remember PM'ng for some information and but b getting a reply; although after all this time I could be mistaken.

 

[simond]

As I said, Dan, present company excepted!

At the time all the regulars were demanding information, but it turned out those I took the trouble to respond to were only interested in trying to trip me up, so I stopped reciprocating.

I have no vested interest in accumulators other than we use them as one of the tools of providing successful heating and water installations to customers.

 

[Dan Robinson]

Fitting a 750 today .... If I ever get there...... Bloody underground strike chaos in the roads in Laaaandan.

 

[Biggles..]

What you need is a break tank and booster set.

 

[Agile]

I have to say that for most applications I would favour a tank and booster pump ( fitted with manual bypass in case of pump or electricity failure. ]

Tony

 

[simond]

A good deal of our business comes from taking tank and booster sets out!

More the merrier.