On Mon, 13 Nov 2017 07:15:58 +0000, alan_m wrote:

On 13/11/2017 04:27, Johnny B Good wrote:


The important lesson from this experience is that anyone upgrading
from
a conventional 'tried and tested' ball cock float valve to one of these
new fangled servo operated float valves is to make sure that the
overflow can cope with the effects of a shut off failure.



Are you sure the correct restrictor was fitted in the first place? Often
two alternative restrictors are supplied and/or there is an adjustment
for the inlet water pressure.

Yes, there was only the one restrictor mentioned in the instruction
leaflet and only referred to the removal of a pre-fitted flow restrictor
to improve filling performance on low pressure supplies.


IMO many of the faults with the valves your describe may be due to a
inlet water pressure too high for the device.

You can also have problems with very low pressure preventing the valve
from shutting off the supply (but this situation is less of a problem for
the overflow). In any case the flow restrictor doesn't effect the static
water pressure which would be the key element with their use on
excessively high pressure supplies.


You could use the new service valve as a restrictor to see if if a lower
inlet flow cures some of the obvious problems. The hole on a restrictor
is usually a small fraction of the diameter of a 15mm pipe so a full
bore service valve was probably unnecessary.

Aside from the much needed convenience of fitting an isolator valve,
using it to test the effect of additional flow restriction was also a
consideration as to why it would be worth the extra trouble of fitting
one before attempting any more fettling to eliminate the risk of more
toilet floods.

The restrictor takes the form of a tapered fluted plug in the Fluidmaster
valves whilst, if memory serves, the other make of servo float valve in
the loft header tank took the form of a tapered spiral which I removed to
compensate for the drop in supply pressure due to the higher altitude
(hence my actually seeing said flow restrictor gizmo on this brand of
valve as opposed to not seeing the ones pre-fitted to the Fluidmasters).


I've had ball-cocks (temporally) fail open when the water utility
company have been undertaking local works and grit/dirt has entered the
supply and has prevented the value from closing properly. I've found the
new style of valve to be no more unreliable than the older ball cock
type valve.

The major difference is that such ball cock float operated valves tend
to allow a trickle of water through rather than remain jammed fully open.
This greatly minimises the risk of the overflow becoming overwhelmed in
its failsafe task of dumping the excess water out of the fabric of the
building. The servo operated float valves can, for any number of reasons,
fail to shut off, resulting in an unabated filling of the tank or cistern
that the overflow might be unable to keep pace with. When the diaphragm
fails to properly seal (wear or grit) in a servo float valve, the
resulting leakage is easily dealt with by the overflow as per the similar
situation with conventional float valves.

As it happened, I did see some weepage after swapping out the valves
which over some 2 or 3 hours eventually raised the level to that of the
overflow which was able to limit any further rise in level. The problem
seemed to slowly disappear with some intermittency and now seems to have
finally settled down.

I suspect it was all the removal and refitting of the diaphragm trying
to figure out whether the actuator pin was supposed to poke through to
the other side of the diaphragm or not before I finally spotted the tiny
hole in the central shank part that the pin was sliding past, prompting
me to take a much closer view of the actuating pin itself to discover a
'waisted' section that acted as a slide valve against the tiny hole. It's
this arrangement that gives the servo action a toggling effect utilising
the water pressure to rapidly "turn the tap off and on". Unfortunately,
it's the very small dimensions of the slide valve components that makes
them susceptible to grit particles in the water supply.

I haven't worked out whether a blockage by a particle of grit results in
a failure to open (failsafe) or a failure to close (unsafe failure). I'd
like to be able to think that the valve will fail safe in the event of a
grit induced blockage but that at the moment is merely a pious hope based
on faith that the designers knew what they doing. If they *did* know what
they were doing, I'd expect mention of this failsafe behaviour in the PR
materials so a look at FluidMaster's marketing bull**** on their website
might offer some reassurance on this point.

However, aside from the failed one way air breaker valves and the
unintended water spray, the valves did function fine with at least one
working for a good 7 or 8 years without failure, so they seem reliable
enough if you ignore the issue of backspraying via the air breaker vents.

I'm guessing the ornamental hose nipple is a fossil of an earlier design
sans the one way valve and additional vents where the modified version
did away with a seperate drilling out step and the fitting of a piece of
plastic tubing. My modification most likely restored the missing stages
of production with the blocking of the vents cancelling the design change
made in the moulding.

I suspect that storing the other valve (with the SA tape removed) in a
container full of lime scale remover for a few weeks or months, will
'cure' the spray back fault. Whether I'd want to use such remedial
treatment, beyond satisfying my curiosity, as a regular scheduled
maintenance action seems most unlikely since the drill/hot glue fix looks
like the least effort for a more permanent solution. I'd rather avoid
swapping valves over every 6 to 12 months just to rotate them through the
bath of lime scale removal solution.

--
Johnny B Good