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

On Jan 9, 7:25*pm, Mathew Newton wrote:
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


There may be no air in your expansion vessel. The air provides a
cushion against these effects.

Hi Harry,

On Jan 9, 7:33*pm, harry 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 09/01/2012 19:42, Mathew Newton wrote:
Hi Harry,

On Jan 9, 7:33 pm, 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
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

On Jan 9, 7:42*pm, Mathew Newton wrote:
Hi Harry,

On Jan 9, 7:33*pm, harry 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
Sounds a possibility. If the pressure is too high,it may as well not
be there.

On Jan 10, 7:51*am, Lobster wrote:
On 09/01/2012 19:42, Mathew Newton wrote:

Hi Harry,

On Jan 9, 7:33 pm, *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
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

If you have a mains pressure water/unvented water heater+ PRV, there
is an expansion vessel in the cold water supply too.
Sometimes the PRV can stick causing juddering.

On Jan 10, 7:51*am, Lobster wrote:

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.

Have you tried fiddling with the main stopcock - turning that down to
reduce flow rate can often help in such situations.

Will give that a go and see how it effects things (and, if so, whether
the reduced flow remains acceptable).

Mathew

On Jan 10, 8:11*am, harry 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
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

On 09/01/2012 19:42, Mathew Newton wrote:
Hi Harry,

On Jan 9, 7:33 pm, 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

That sounds to me like too high a charge pressure if the static pressure
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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checked.

On Jan 10, 10:27*am, Roger Mills 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.

I would be inclined to reduce the charge pressure to 2 bar, and see what
happens.

Will do.

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.

If I can find the details I may well try that, if only as an
interesting exercise anyway.

Thanks for all the input gents, I will feedback the results.

Mathew

On Jan 10, 10:27*am, Roger Mills wrote:

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... ;-)

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

Mathew Newton wrote:
On Jan 10, 10:27 am, Roger Mills wrote:

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... ;-)

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...?!

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.

Tim

On Jan 10, 9:36*pm, Tim 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
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

On 10/01/2012 19:35, Mathew Newton wrote:
On Jan 10, 10:27 am, Roger wrote:

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... ;-)

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

Right, let's have a go.

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!
--
Cheers,
Roger
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checked.

On Jan 10, 11:06*pm, Roger Mills wrote:

Right, let's have a go.

Thanks Roger - really appreciate it!

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
necessary calculations it certainly looks correct and is at least the
right order of magnitude!

Thanks again,

Mathew