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Judder / water hammer with an unvented HW cylinder
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Mathew Newton
Jan 9, 2012, 2:25:38 PM1/9/12
to
We've recently moved into a new(ish) house with a Range Tribune
unvented HW cylinder and are suffering (being annoyed by) juddering /
water hammer and would be grateful for some advice as to how to
eliminate it if possible.
Some observations which may or may not be relevant:
1. The noise appears to be coming from the pressure reducing valve
(and not loose pipework etc) fitted adjacent to the cylinder.
2. The expansion vessel pressure is 3 bar (measured with the incoming
mains off and a some taps open) as per the manufacturers installation
instructions.
3. The incoming water pressure is 2 bar (measured before and after the
PRV).
4. The PRV setting is unknown.
5. The noise is a single thud from the PRV when a tap is opened and,
more evidently, when it is closed. The cold water taps appear to cause
a louder noise than the hot. Even the kitchen, connected straight off
the incoming mains (i.e. upstream of the PRV) causes a thud.
5. The shower, particularly when first used in the morning, causes
repeated thuds for half and second or so if turned on quickly.
Does any of the above point to anything in particular? Are there other
details I've missed out that could be pertinent?
Grateful for any pointers,
Mathew
unvented HW cylinder and are suffering (being annoyed by) juddering /
water hammer and would be grateful for some advice as to how to
eliminate it if possible.
Some observations which may or may not be relevant:
1. The noise appears to be coming from the pressure reducing valve
(and not loose pipework etc) fitted adjacent to the cylinder.
2. The expansion vessel pressure is 3 bar (measured with the incoming
mains off and a some taps open) as per the manufacturers installation
instructions.
3. The incoming water pressure is 2 bar (measured before and after the
PRV).
4. The PRV setting is unknown.
5. The noise is a single thud from the PRV when a tap is opened and,
more evidently, when it is closed. The cold water taps appear to cause
a louder noise than the hot. Even the kitchen, connected straight off
the incoming mains (i.e. upstream of the PRV) causes a thud.
5. The shower, particularly when first used in the morning, causes
repeated thuds for half and second or so if turned on quickly.
Does any of the above point to anything in particular? Are there other
details I've missed out that could be pertinent?
Grateful for any pointers,
Mathew
harry
Jan 9, 2012, 2:33:06 PM1/9/12
to
cushion against these effects.
Mathew Newton
Jan 9, 2012, 2:42:28 PM1/9/12
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Hi Harry,
On Jan 9, 7:33 pm, harry <haroldhr...@aol.com> wrote:
> There may be no air in your expansion vessel. The air provides a
> cushion against these effects.
I've measured the expansion vessel air pressure (with the supply off
and pipework pressure removed) to be 3 bar.
Given my low (2 bar) incoming pressure could it be that the expansion
vessel is set too high i.e. not able to absorb the pressure ripples
resulting from sudden tap closures?
Mathew
On Jan 9, 7:33 pm, harry <haroldhr...@aol.com> wrote:
> There may be no air in your expansion vessel. The air provides a
> cushion against these effects.
and pipework pressure removed) to be 3 bar.
Given my low (2 bar) incoming pressure could it be that the expansion
vessel is set too high i.e. not able to absorb the pressure ripples
resulting from sudden tap closures?
Mathew
Lobster
Jan 10, 2012, 2:51:09 AM1/10/12
to
On 09/01/2012 19:42, Mathew Newton wrote:
> Hi Harry,
>
> On Jan 9, 7:33 pm, harry<haroldhr...@aol.com> wrote:
>
>> There may be no air in your expansion vessel. The air provides a
>> cushion against these effects.
>
> I've measured the expansion vessel air pressure (with the supply off
> and pipework pressure removed) to be 3 bar.
But presumably the vessel you're talking about is on the central heating
> Hi Harry,
>
> On Jan 9, 7:33 pm, harry<haroldhr...@aol.com> wrote:
>
>> There may be no air in your expansion vessel. The air provides a
>> cushion against these effects.
>
> I've measured the expansion vessel air pressure (with the supply off
> and pipework pressure removed) to be 3 bar.
circuit, not the hot water one?
Have you tried fiddling with the main stopcock - turning that down to
reduce flow rate can often help in such situations.
Might be helpful to add in a small (potable water) expansion vessel into
the mains water system? I've done that after suffering similar symptoms
- helped a bit but TBH I'm still having to live with a fair amount of
noise :(
David
harry
Jan 10, 2012, 3:11:45 AM1/10/12
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be there.
harry
Jan 10, 2012, 3:14:09 AM1/10/12
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is an expansion vessel in the cold water supply too.
Sometimes the PRV can stick causing juddering.
mathewja...@googlemail.com
Jan 10, 2012, 3:39:38 AM1/10/12
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> But presumably the vessel you're talking about is on the central heating
> circuit, not the hot water one?
No, it's definitely the HW one.
> circuit, not the hot water one?
> Have you tried fiddling with the main stopcock - turning that down to
> reduce flow rate can often help in such situations.
the reduced flow remains acceptable).
Mathew
mathewja...@googlemail.com
Jan 10, 2012, 3:42:11 AM1/10/12
to
On Jan 10, 8:11 am, harry <haroldhr...@aol.com> wrote:
> Sounds a possibility. If the pressure is too high,it may as well not
> be there.
Yeah that's what I was thinking. And, if in 'normal' circumstances the
> Sounds a possibility. If the pressure is too high,it may as well not
> be there.
role of the PRV is to limit the working pressure to 3 bar then to me
it is understandable that the EV should also have a pre-charge
pressure of 3 bar such that it is in a neutral state prior to heating.
If I can only reach 2 bar then mine isn't in this state and, as say,
going to have less of an effect.
Will drop the pressure a bit and see how things go.
Mathew
Roger Mills
Jan 10, 2012, 5:27:08 AM1/10/12
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On 09/01/2012 19:42, Mathew Newton wrote:
of the incoming mains is only 2 bar. When cold, the water in the
cylinder will be at 2 bar, but when it heats up it will very rapidly
reach 3 bar in order to be able to compress the air in the expansion
vessel. A more gentle expansion would be better.
Is there a pressure relief valve which spills water to the outside world
once a certain pressure is exceeded? What is that set at?
I would be inclined to reduce the charge pressure to 2 bar, and see what
happens.
If all else fails, you may need to do some calculations! If you know the
capacities of the cylinder and of the expansion vessel and the charge
pressure, you can work out what the rise in pressure will be when the
water is heated from (say) 5 degrees to 60 degrees - and make sure that
this is below the blow-off pressure.
--
Cheers,
Roger
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Please reply to Newsgroup. Whilst email address is valid, it is seldom
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mathewja...@googlemail.com
Jan 10, 2012, 8:12:29 AM1/10/12
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On Jan 10, 10:27 am, Roger Mills <watt.ty...@gmail.com> wrote:
> Is there a pressure relief valve which spills water to the outside world
> once a certain pressure is exceeded? What is that set at?
There is, and from memory I believe it is set (fixed) to 6bar.
> Is there a pressure relief valve which spills water to the outside world
> once a certain pressure is exceeded? What is that set at?
> I would be inclined to reduce the charge pressure to 2 bar, and see what
> happens.
> If all else fails, you may need to do some calculations! If you know the
> capacities of the cylinder and of the expansion vessel and the charge
> pressure, you can work out what the rise in pressure will be when the
> water is heated from (say) 5 degrees to 60 degrees - and make sure that
> this is below the blow-off pressure.
interesting exercise anyway.
Thanks for all the input gents, I will feedback the results.
Mathew
Mathew Newton
Jan 10, 2012, 2:35:36 PM1/10/12
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> If all else fails, you may need to do some calculations! If you know the
> capacities of the cylinder and of the expansion vessel and the charge
> pressure, you can work out what the rise in pressure will be when the
> water is heated from (say) 5 degrees to 60 degrees - and make sure that
> this is below the blow-off pressure.
Okay Roger, and any other clever people willing to dive in... ;-)
> capacities of the cylinder and of the expansion vessel and the charge
> pressure, you can work out what the rise in pressure will be when the
> water is heated from (say) 5 degrees to 60 degrees - and make sure that
> this is below the blow-off pressure.
Figures as follows:
- Cylinder volume = 150L
- EV volume = 12L
- EV charge pressure = 2 bar (for this test case, i.e. same as the
mains pressure)
- HW pipework length = 30m (approx)
- Blow-off pressure = 6 bar
Now, where do I go next...?!
Mathew
Tim
Jan 10, 2012, 4:36:05 PM1/10/12
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your system. If it isn't, you'll see water regularly dripping from the
blow-off valve. You can't (indeed, mustn't) adjust the blow-off pressure
relief valve which is preset.
Tim
Mathew Newton
Jan 10, 2012, 4:54:00 PM1/10/12
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On Jan 10, 9:36 pm, Tim <timdownie2...@yahoo.co.uk> wrote:
> > Now, where do I go next...?!
>
> Um, nowhere really. I'm sure the expansion vessel will be "big enough" for
> your system. If it isn't, you'll see water regularly dripping from the
> blow-off valve. You can't (indeed, mustn't) adjust the blow-off pressure
> relief valve which is preset.
Of course, it was more for curiosity's sake than anything else. I've
> > Now, where do I go next...?!
>
> Um, nowhere really. I'm sure the expansion vessel will be "big enough" for
> your system. If it isn't, you'll see water regularly dripping from the
> blow-off valve. You can't (indeed, mustn't) adjust the blow-off pressure
> relief valve which is preset.
always appreciated seeing the the theoretical mechanics behind what I
subsequently can verify in practice. Unfortunately in this case I'm
out of my depth before I've even started. I dare say there as once a
time when I could've done it but, alas, like so many things as I
didn't use it I did indeed lose it... ;-)
Mathew
Roger Mills
Jan 10, 2012, 6:06:32 PM1/10/12
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Water has a volumetric coefficient of thermal expansion of 207 * 10^-6
per degree at 20degC. If we assume that this doesn't vary over the
temperature range in question, if we heat the water from 5degC to 60degC
(i.e. 55 degrees) it will expand by a factor of 207 * 55 / 10^6 = 0.011
So 150L will expand by 150 * 0.011 = 1.7 litres
So the volume of air in the expansion vessel will reduce from 12L to 10.3L
So, at a first approximation, its pressure will rise to 2 * 12 / 10.3 =
2.33 bar
So that won't get anywhere near the blow-off pressure of 6 bar.
[If the charge pressure is 3bar, it would rise to 3.5 bar which is still
ok - but would provide less resilience against water hammer].
Hopefully others will check my calculations, to make sure I haven't got
any decimal points in the wrong place!
Mathew Newton
Jan 11, 2012, 5:08:58 AM1/11/12
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Thanks Roger - really appreciate it!
> So, at a first approximation, its pressure will rise to 2 * 12 / 10.3 =
> 2.33 bar
necessary calculations it certainly looks correct and is at least the
right order of magnitude!
Thanks again,
Mathew
> So, at a first approximation, its pressure will rise to 2 * 12 / 10.3 =
> 2.33 bar
> Hopefully others will check my calculations, to make sure I haven't got
> any decimal points in the wrong place!
Caveated by my earlier admission of not fully understanding the
> any decimal points in the wrong place!
necessary calculations it certainly looks correct and is at least the
right order of magnitude!
Thanks again,
Mathew
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