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PostPosted: Wed Sep 10, 2003 11:43 am 
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Joined: Wed Sep 10, 2003 11:34 am
Posts: 5
I have an Ariston indirect unvented water cylinder. The system works excellent with good flow rates but suffers from an anoying 'knocking' noise when the hot water is first run (tap/washing machine/shower turned on) following a period of heating the water; i.e when the cylinder is at a higher pressure that the incoming cold feed. It is made worse when the incoming water pressure is low or a cold tap/toilet is running. The longer the heating period (higher pressure)the louder and longer the noise period.

The noise appears to come from the non-return valve opening and shutting very quickly (oscillating). All the valves are as supplied with the cylinder. The expansion vessel is at the correct pressure.

Can anyone suggest the source of the problem and a cure!


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PostPosted: Wed Sep 10, 2003 2:14 pm 
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Joined: Wed Sep 10, 2003 11:34 am
Posts: 5
Thanks for the comments.

The installations has made the noise from new and is still less than a year old.

The noise could be coming from the pressure reducing valve - its a job to tell as the system/pipes resonates.

The EV pressure was taken when the system was dry.

Drake.


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 Post subject:
PostPosted: Wed Sep 10, 2003 6:29 pm 
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Joined: Tue Apr 23, 2002 2:55 pm
Posts: 2845
Location: North London ONLY
There aren't any stop cocks AFTER the pressure reducing valve? Went to a Megaflow the other day with this and there was a hell of a racket when the taps were opened.



Regards :)

Dan Robinson
Jennings Heating & Plumbing
CORGI - 138845
Email: dan.robinson@blueyonder.co.uk
Phone 0777 5731339

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Regards :)

Dan Robinson
Jennings Heating & Plumbing
CORGI - 138845
Email: dan.robinson@blueyonder.co.uk
Phone 0777 5731339


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 Post subject:
PostPosted: Wed Sep 10, 2003 9:35 pm 
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Joined: Tue Sep 24, 2002 10:02 pm
Posts: 3337
There can be now Dan, on the new models the PRV can be fitted remote.

scruff


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 Post subject:
PostPosted: Wed Sep 10, 2003 9:45 pm 
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Joined: Tue Apr 23, 2002 2:55 pm
Posts: 2845
Location: North London ONLY
I know mate, my bruv's is under his front door... But you can not use loose jumpered stop-cocks... which was what I was referring too.

Chris... any hcance of thoswe beta-blockers? After the week I've had I think I need'em...

Still Caradon training day tomorrow - should be fun, got one of those duff Response gas valves to strip down and see whats inside.



Regards :)

Dan Robinson
Jennings Heating & Plumbing
CORGI - 138845
Email: dan.robinson@blueyonder.co.uk
Phone 0777 5731339

_________________
Regards :)

Dan Robinson
Jennings Heating & Plumbing
CORGI - 138845
Email: dan.robinson@blueyonder.co.uk
Phone 0777 5731339


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 Post subject:
PostPosted: Thu Sep 11, 2003 9:26 am 
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Joined: Wed Sep 10, 2003 11:34 am
Posts: 5
Hi all, thought you may like to know the response from Ariston. I have not tried the suggested cure but will let you know.

"The problem you mention is a standard one when the mains
supply pressure is not very good. The expansion vessel which accompanies the
cylinder is pre-pressurized at 3.5 bar on the basis that that would be the
usual charge pressure in the cylinder. If the mains pressure is
significantly lower, when the cylinder first discharges the 'expanded'
pressure i.e. when used first thing in the morning etc., the expansion
vessel and the pressure reducing valve letting water into the cylinder
'fight' giving rise to the juddering noise. The cure is to let the excess
air pressure out of the expansion vessel, i.e. drop the charge pressure from
3.5 bar to about 1/4 bar above the mains pressure".


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PostPosted: Thu Sep 11, 2003 9:51 am 
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Joined: Tue Sep 24, 2002 10:02 pm
Posts: 3337
Sounds reasonable, I would query the integrity of the imformation.

A, The pressure in the vessel sounds very high.

B, The pressure reducing valve is set at a constant pressure, normally 2bar, if the cylinder is greater due to heated water expansion, no further water will enter the cylinder until the pressure drops.

C, On some makes/models the PRV requires a 3m pipe run for expansion to take place.

D, The temperature and pressure relief valve will operate at either 95C or 4bar pressure in a fault condition.

E, The mains pressure should not fall below the operating pressure of 2.5bar.

scruff.


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 Post subject:
PostPosted: Mon Sep 15, 2003 9:10 am 
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Joined: Wed Sep 10, 2003 11:34 am
Posts: 5
I have now carried out some further checks.

The standing water pressure measured at an outside tap adjacent to where the water main enters the house is 3.2 bar. However, this soon lowers with the use of water; kitchen tap on full 1.6 bar; toilet refilling 2.6 bar; bath tap on full 1.0 bar. We are in a rural area that suffers from low pressure!

The problem with the unvented cylinder, as I see it,is that the following sequence of events is taking place:
1. After a period of heating and water expansion, the cylinder at a higher pessure than the incoming water main (> 3.2 bar). The pressure reducing valve is off.

2. Turning on the hot water allows water flow, the pressure will reduce. At a point below 3.2 bar the pressure reducing valve will open and allow water to enter the cylinder.

3. The flow of water causes the incoming water pressure to lower. When below the the cylinder pressure the valve closes again.

4. The incoming pressure returns to 3.2 bar, the valve opens again.

5. This all repeats, causing the juddering noise until all the extra pressure in the cylinder is released.

The way we can prevent the juddering is by running a hot tap slowly first thing is the morning to release the extra pressure.

I have tried reducing the expansion vessel pressure as suggested by Ariston to 3.0 bar (from 3.5 bar) but it does not make any difference. In any case, Ariston suggested the EV pressure should be 1/4 bar higher than the mains pressure. This would put it back to 3.5 bar.

Are we stuck with this problem or are there solutions for this type of case?


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 Post subject:
PostPosted: Mon Sep 15, 2003 10:03 am 
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Joined: Tue Sep 24, 2002 10:02 pm
Posts: 3337
I would turn the PRV down to say 2bar and give it a try.

Alternative is to up the mains to a larger pipe size to give you more volume.

scruff.


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 Post subject:
PostPosted: Mon Sep 15, 2003 10:21 am 
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Joined: Thu Jan 09, 2003 11:40 am
Posts: 3449
Location: NW London
I agree with your clever diagnosis of the problem.

As far as a cure is concerned then obviously improving the flow rate is the best but probably expensive.

A possible improvement might be obtained by fitting a shock arrester on the mains close to the PRV. But better if specifications allow might be a larger, say 10 litres, potable expansion vessel. These are available because they are used on pumps etc.

However this is only a suggestion and may not work. If I was faced with the problem, I would fit a spare vessel on test to see what the effect was.

And was the installer certificated for unvented???

Tony Glazier
Agile Services

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