Just purchased a replacement kitchen tap, that came with a bylaw 30 kit
(look like a one way valve for the hot side (red arrow))
Q. do I need to fit this?
Mains cold water and gravity hot water (cold storage tank in loft)
The non return valve is normally on the cold side, so that water from the
tank cant get into the mains water.
If the mains fails, water could get into it if both the taps are turned on &
there is no non return valve.
Better taps have a dual spout & doesn't need this, the water mixes out of a
On Mon, 27 Oct 2003 02:12:48 GMT, BigWallop wrote:
Apart from the possibility of tank water getting back into the mains, the
lack of this separation in the spout opens up the possibility of the tank
water being drunk inadvertantly:
run the hot water for washing up
turn tap off
come back later for a drink, the first water to come out of the spout when
you turn the cold tap is formerly warm water from the tank. If you run the
tap for a second first, no problem, but how many think about this.
I always let the water run a bit before I drink it, and the said water is
from an under sink filter in a single tap!
I would be surprised if most people place glass under tap, turn on tap, wait
for glass to fill, then turn off tap
Most people I know will turn on tap, move glass under it, move glass away
then turn off the tap.
First, I have no plumbing expertise at all.
But, I'd have thought that there was *no* chance of water from the hot
water side making its way into the cold, as the pressure of the mains
is much higher than the "domestic side"
This was proven to me when my Chemistry teacher challenged me to put
my thumb on the cold water tap and stop the water. I'd said it could
be done in class, she challenged me to try it at home. She was right,
I was very wet. I could stop the hot water supply though.
If the mains fails, then there's no water coming through, but when the
supply starts up again...
Just my 2d.
RD400E, Bandit 12, XR400R (in length of service order)
The problem can occur if the mains fails.
IF the mains fails, and the tap is turned on to hot and cold, the hot water
can be sucked into the mains system
Just like if you turn off you water, and turn a tap on upstairs and
downstairs, the water will flow backwards in the pipes upstairs
IMHO the water company should fit one way valves on your supply!
I think you have the wrong sort of tap, which is only suitable for high
pressure (ie combi) hot water systems. As others have said, the non return
valve is to stop contamination of the main cold water because the water is
mixed in the body of the tap rather than at the end of the spout.
Since your hot water is gravity fed, if you open hot and cold taps at the
same time, the higher pressure mains cold will push the lower pressure hot
water back up the pipe.
I don't know whether putting the valve on the hot side would physically
work (if the valve is designed for mains pressure to operate it) to stop
the cold going back up into the hot, but the difference in pressure is
likely to stop much hot water coming out of the tap when the cold is on. It
wouldn't comply with Bylaw 30 though.
Good points, nothing on the tap box to say full pressure systems only,.
Water is definitely mixed in the body of the tap (if I had know this I
wouldn't have brought it)
must make sure that I remember to run tap on full cold first before
taking drinking / cooking water, and slow time find another tap her
indoors likes (that doesn't, mix the water inside)
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