Hi all

I have recently purchased a Hansgrohe Focus S mixer tap for a downstairs WC
re-furb.
The installation instructions state that equal pressure is required on both
hot and cold feeds, though the suppliers claimed it would work with mains
cold and gravity hot.
My concern is that, not understanding the internals, it may be possible for
the mains water to back fill the hot water cold storage tank.
So fit a non-return valve on the hot feed?
I have done that in the bathroom, and the hot flow is seriously compromised!
Is there a non-return valve available with a weak spring so that flow is far
less affected?
Do I actually need a nrv in this situation?

Any informed comment appreciated.

TIA

Phil

On 2007-07-07 22:15:40 +0100, "thescullster" said:

Hi all

I have recently purchased a Hansgrohe Focus S mixer tap for a downstairs WC
re-furb.
The installation instructions state that equal pressure is required on both
hot and cold feeds, though the suppliers claimed it would work with mains
cold and gravity hot.
My concern is that, not understanding the internals, it may be possible for
the mains water to back fill the hot water cold storage tank.
So fit a non-return valve on the hot feed?
I have done that in the bathroom, and the hot flow is seriously compromised!
Is there a non-return valve available with a weak spring so that flow is far
less affected?
Do I actually need a nrv in this situation?

Any informed comment appreciated.

TIA

Phil


I have the same situation as you know, although with a different model.
I am not sure about the Focus S, but the Uno has a single spout and
the mixing occurs in the body of the valve. Some sink mixers have a
concentric arrangement that ends at the spout exit, so no possibility
of water being passed back unless some kind of blocked tube were
attached.

The only way that you could get back filling with the Hansgrohe tap is
to put your finger over the spout and open both sides.

More to the point would be the requirements to avoid cross
contamination. AIUI, the mains water is fluid category 1 and the HW
supplier sourced via the roof tank is fluid category 2. For showers
with a flexible hose, there are supposed to be check valves on both
supplies because of the possibility that the shower head is dropped
into the shower tray or even the toilet (category 5).

I am not sure that there is a requirement to protect the supplies to
the basin tap. At any rate, what I have done is to put a check valve
in the cold supply only plus a service valve with small aperture.
There is a need to reduce flow anyway. The hot is connected directly
at present. I am going to check the point with WRAS, but I believe
that this meets the cross contamination requirements.

I don't think that the risk of cold mains being fed to the roof storage
tanks is an issue. The warning pipe of the tank would highlight that
and it does require someone to deliberately block the spout

On Sat, 7 Jul 2007 22:57:19 +0100, Andy Hall
wrote:

I don't think that the risk of cold mains being fed to the roof storage
tanks is an issue. The warning pipe of the tank would highlight that
and it does require someone to deliberately block the spout

Don't forget that most monoblocs have a sparkler or whatever on to mix
the hot/cold as it leaves the tap. This is equivalent to a thumb over
the tap, particularly on cheap taps. It caused me months of trouble
with the roof tank overflowing until the combi was installed. I was
fine with it but everyone else in the house seemed incapable of not
overflowing the tank out the overflow pipe.

On 2007-07-07 23:43:16 +0100, EricP said:

On Sat, 7 Jul 2007 22:57:19 +0100, Andy Hall
wrote:

I don't think that the risk of cold mains being fed to the roof storage
tanks is an issue. The warning pipe of the tank would highlight that
and it does require someone to deliberately block the spout

Don't forget that most monoblocs have a sparkler or whatever on to mix
the hot/cold as it leaves the tap.

This one has such a fitting but it's adjustable by removing a component
for low pressure.


This is equivalent to a thumb over
the tap, particularly on cheap taps.

Up to a point. The effect would depend on the resistance to flow at
the spout for the mains flow and the difference in head. I would
expect it to be worse on a first floor tap. Reducing the flow on the
mains side would also reduce the effect. It isn't really a thumb
over spout situation because there is still flow.


It caused me months of trouble
with the roof tank overflowing until the combi was installed. I was
fine with it but everyone else in the house seemed incapable of not
overflowing the tank out the overflow pipe.

thescullster wrote:

Is there a non-return valve available with a weak spring so that flow is far
less affected?

On some you can remove the spring altogether. Since all you are seeking
to prevent is back flow pushed by positive pressure from the cold then
it should still do this without a spring. Using one designed for 22mm
pipe would be another way of reducing the impact.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"Andy Hall" wrote


I have the same situation as you know, although with a different model.

Yes, thanks for the recommendation.
Assuming it performs OK, I have a smart mixer which appears of good quality
for £73 - the alternative supplier's offerings, some of dubious quality,
were in the 100-160 range.

Uno has a single spout and the mixing occurs in the body of the valve.

What's to stop the cold water entering the valve body and leaving via the
hot feed route rather than the spout?
I suppose a lot will depend on the bore of the inner channels relative to
the spout size.
EricP's experience suggests that it doesn't take much if any restriction to
cause this issue.


The only way that you could get back filling with the Hansgrohe tap is to
put your finger over the spout and open both sides.

More to the point would be the requirements to avoid cross contamination.
AIUI, the mains water is fluid category 1 and the HW supplier sourced via
the roof tank is fluid category 2. For showers with a flexible hose,
there are supposed to be check valves on both supplies because of the
possibility that the shower head is dropped into the shower tray or even
the toilet (category 5).

I am not sure that there is a requirement to protect the supplies to the
basin tap. At any rate, what I have done is to put a check valve in the
cold supply only plus a service valve with small aperture.

I know it is kind of overkill, but I was considering 2 service valves on the
cold feed.
The downstream one would be used to throttle the flow with the upstream
being on-off only.
The reason being that ball valves are not intended for flow control and
running them partly open can cause seat wear.
The downstream valve would be in a "really easy to switch" location.

There is a need to reduce flow anyway. The hot is connected directly at
present. I am going to check the point with WRAS, but I believe that
this meets the cross contamination requirements.



Please post new thread if you get a response from your WRAS enquiry


I don't think that the risk of cold mains being fed to the roof storage
tanks is an issue. The warning pipe of the tank would highlight that and
it does require someone to deliberately block the spout



Thanks once again Andy, help as always greatly appreciated

Phil

"John Rumm" wrote

On some you can remove the spring altogether. Since all you are seeking to
prevent is back flow pushed by positive pressure from the cold then it
should still do this without a spring. Using one designed for 22mm pipe
would be another way of reducing the impact.

Good call John, I'll check if the spring is removable

Phil

On 2007-07-08 08:10:08 +0100, "thescullster" said:


"Andy Hall" wrote


I have the same situation as you know, although with a different model.

Yes, thanks for the recommendation.
Assuming it performs OK, I have a smart mixer which appears of good quality
for £73 - the alternative supplier's offerings, some of dubious quality,
were in the 100-160 range.

Uno has a single spout and the mixing occurs in the body of the valve.

What's to stop the cold water entering the valve body and leaving via the
hot feed route rather than the spout?

Because the way out through the spout presents a lower resistance than
the way back up the hot supply plus the head from the cold tank in the
roof.

This is a pressure/flow issue. It will partly depend on the location
of the tap - i.e. likely to be worse upstairs where the head from the
tank is less - the cold is less as well but this is a matter of
pressure difference.



I suppose a lot will depend on the bore of the inner channels relative to
the spout size.
EricP's experience suggests that it doesn't take much if any restriction to
cause this issue.

I think that it could be resolved by reducing the cold flow to the same
rate as that of the hot when the tap is fully open.




The only way that you could get back filling with the Hansgrohe tap is to
put your finger over the spout and open both sides.

More to the point would be the requirements to avoid cross contamination.
AIUI, the mains water is fluid category 1 and the HW supplier sourced via
the roof tank is fluid category 2. For showers with a flexible hose,
there are supposed to be check valves on both supplies because of the
possibility that the shower head is dropped into the shower tray or even
the toilet (category 5).

I am not sure that there is a requirement to protect the supplies to the
basin tap. At any rate, what I have done is to put a check valve in the
cold supply only plus a service valve with small aperture.

I know it is kind of overkill, but I was considering 2 service valves on the
cold feed.
The downstream one would be used to throttle the flow with the upstream
being on-off only.

You could do that. It would save readjusting if you need to turn off
the service valves.


The reason being that ball valves are not intended for flow control and
running them partly open can cause seat wear.
The downstream valve would be in a "really easy to switch" location.

There is a need to reduce flow anyway. The hot is connected directly at
present. I am going to check the point with WRAS, but I believe that
this meets the cross contamination requirements.



Please post new thread if you get a response from your WRAS enquiry

I'm going to call them tomorrow. I've done so before on the showers
issue because I couldn't think of a reason why water from a shower
could enter the plumbing.

They are in Gwent and a very excitable Welshman with a high voice (do
you remember Clive Jenkins, the union leader?) explained that there
are "sections of the community" who remove the shower head from the
hose and use it to clean "where the sun don't shine" and then drop the
hose into the toilet. Then somebody downstairs turns on the hot tap
rather than the cold for drinking water..... It seemed implausible -
not the ablutionary aspect - toilets in the Arab world are generally
fitted with a little trigger operated shower with cold water - yes...
but the siphoning. Nevertheless, I fitted the valves.

One trick is to fit larger ones than the nominal pipe size - i.e. 22 or
even 28mm to the hot.







I don't think that the risk of cold mains being fed to the roof storage
tanks is an issue. The warning pipe of the tank would highlight that and
it does require someone to deliberately block the spout



Thanks once again Andy, help as always greatly appreciated


You're welcome.

On 2007-07-08 08:11:19 +0100, "thescullster" said:


"John Rumm" wrote

On some you can remove the spring altogether. Since all you are seeking to
prevent is back flow pushed by positive pressure from the cold then it
should still do this without a spring. Using one designed for 22mm pipe
would be another way of reducing the impact.

Good call John, I'll check if the spring is removable

Phil

You can usually see the spring, but the valve body is pressed into place.

Solution is to clip out part of the spring near the end using a pair of
small side cutters etc.

"thescullster" wrote in message
...

"John Rumm" wrote

On some you can remove the spring altogether. Since all you are seeking
to prevent is back flow pushed by positive pressure from the cold then it
should still do this without a spring. Using one designed for 22mm pipe
would be another way of reducing the impact.

Good call John, I'll check if the spring is removable

Buy a springless (gravity) valve.