On Mon, 13 Nov 2017 10:14:43 +0000, Roger Hayter wrote:

Johnny B Good wrote:



Presumably this 'air breaker' incorporates a one way valve to prevent
spray back. It's rather unfortunate that my experience with two
examples of this valve type have led me to conclude that its design
left rather too much to be desired, ie reliability. However, blocking
the vents and drilling out the pipe connection does offer a reasonably
neat work around to this annoying shortcoming. Presumably, there must
have been some reason why the design included such a venting route,
subsequently one has to assume, to be superceded by the 'spray back'
prone vent ports.

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.

AMI the vents at the top, like the common collapsible down tube, are
probably to prevent back siphonage. This is necessary to meet water
regulations. So your mods probably make it illegal. Personally I
would not lose an enormous amount of sleep over this, just for interest,
as I say.

Well, the simple act of sealing off the vents with SA tape would
certainly have made it non-compliant but the more considered drilling and
hot melt glue mod to the spare unit would appear to have kept it all
legit.

My best guess for the adornment of a non-functional tubing nipple is
that the design was altered to save the cost of the drilling out stage[1]
and the additional expense of a piece of plastic tubing. Indeed, the
reason as to why the tubing nipple still existed is most likely because
it's easier to machine out an existing mould to incorporate the extra
vents just above what must have been the original domed top and the
minuscule savings in plastic feedstock costs not considered worth the
expense of making a new mould from scratch. Any additional internal
changes to accommodate a one way anti-spray valve would most likely would
have involved changes to a separate smaller plastic moulding used to
complete the final build.

[1] Second guessing here but it's entirely possible that there wasn't a
drilling out stage to begin with. The 'gallery' may have been moulded in
from the start and all that was required to 'blank it off' was a minor
grinding back of the corresponding spigot used in the mould.

Whatever the reason for such an adornment, you can stake your life that
it was driven by economics. A case of let's not burn our boats just yet
before we've proved that what looks like an elegant design solution on
the drawing board doesn't turn out to be a white elephant out in the real
world. The fact that the one way anti spray back valves failed so early
on lends some credence to the belief that it was a design at the early
stages of its transition to a nippleless version.

--
Johnny B Good