How to tell if double glazing has "popped"...

[Mike Deblis]

Hi,

How can you (non-destructively) test double glazing to see if it had "popped" (lost its vacuum) without having to look for moisture inside etc. We have some 10-year-old thinnish (maybe 14mm) double glazing that seems very cold to the touch and is getting condensation on (not in) it. One or two of the panes have definitely gone (they have condensation inside the unit), but if I'm going to have those replaced, I'd like to do any that are failing too...

Is there a sonic or similar method?

Thanks

Mike

[Grunff]

It doesn't have a vacuum.

The vast majority have dried air, a small percentage have argon.

If you're not getting condensation between the panes, the seal is intact.

[Ian Stirling]

Traces of water vapour in the panel may make it very, very slightly more conductive. But, not practically measurable. Argon fill is (IMO) a joke - the molecular weight - and hence conductivity is almost exactly the same as oxygen/nitrogen. CO2 might actually be better.

IIRC, the best insulating gap is around 18mm - so you'd need at least

18+6+4 = 28mm overall. 18mm means a very thin gap - 6+4 = only 8mm or so, which is fairly poor to start with. Even on functioning to spec windows may well feel cold, and have condensation in.

[Ian Stirling]

Oops, missed this. No double glazing has vacuum inside. Consider a 1m^2 window - if it did, it'd have 10 tons of force pushing each pane towards each other. The glass would immediately shatter - if it diddn't have lots of supports.

[Chris Bacon]

They are not evacuated units - they may be filled with special gas, though.

If they're not steamed up, they're OK. 464 units which you seem to have aren't very good insulators anyway.

I don't know of any way to test the soundness of the units.

[Andy Dingley]

The definition of "popped" pretty much depends on whether there's moisture inside. Although they're "sealed units", this is just bog-standard workshop air that gets sealed into them, dried out by a dessicator pack if you're lucky. Only the good ones have anything else as a special filler, and even then it's still atmospheric pressure.

[Blueyonder]

The only evacuated tube commonplace in homes today is the TV tube, and look at how thick the glass is on the from of that to withstand the pressure. TV tubes are held together by a strong metal band just inside the case from the front. If that is removed, then the whole thing will explode spectacularly (and will have your eyes out and most of your face off - so don't even think about experimenting).

-- JJ

[Grunff]

Removing the reinforcing band does not cause the immediate implosion of the tube, and certainly not on smaller tubes. In addition, imploding a tube is rarely as spectacular as most people who've never done it make out.

[Dave Fawthrop]

|On Mon, 16 Jan 2006 09:49:35 +0000 (UTC), "Mike Deblis" | wrote: | |>How can you (non-destructively) test double glazing to see if it had |>"popped" (lost its vacuum) without having to look for moisture inside = etc. | |The definition of "popped" pretty much depends on whether there's |moisture inside. Although they're "sealed units", this is just |bog-standard workshop air that gets sealed into them, dried out by a |dessicator pack if you're lucky. Only the good ones have anything else |as a special filler, and even then it's still atmospheric pressure.

Except for *caravan* double glazing made of two layers of *plastic* which are vented to the inside via a small plug. Which surprisingly works = well.

--=20 Dave Fawthrop

17,000 free e-books at Project Gutenberg! Yorkshire Dialect go to

[Gordon Henderson]

Interestingly enough, a lot of SCUBA divers use argon to inflate their dry suits to make them warmer. I've tried it once, and I didn't notice any difference...

Google for argon in a scuba environment for more details... (including holy wars by people say yes it does, not it doesn't, etc.!!!)

Gordon

[Ian Stirling]

I think you mean outside - though I've never seen one.

[Dave Fawthrop]

|Dave Fawthrop wrote: |> On Mon, 16 Jan 2006 14:19:41 +0000, Andy Dingley =

|> wrote: |>=20 |> |On Mon, 16 Jan 2006 09:49:35 +0000 (UTC), "Mike Deblis" |> | wrote: |> | |> |>How can you (non-destructively) test double glazing to see if it had |> |>"popped" (lost its vacuum) without having to look for moisture = inside etc. |> | |> |The definition of "popped" pretty much depends on whether there's |> |moisture inside. Although they're "sealed units", this is just | |> Except for *caravan* double glazing made of two layers of *plastic* = which |> are vented to the inside via a small plug. Which surprisingly works = well. | |I think you mean outside - though I've never seen one.

No inside, I have just looked on my van, on the drive. =20 Interestingly the small window on the door does not have a plug, never noticed that before 8-0

--=20 Dave Fawthrop

17,000 free e-books at Project Gutenberg! Yorkshire Dialect go to

[Andy Dingley]

TV tubes illustrate how it's easy to resist the presure, but it's the force (pressure over an area) that causes the trouble. The big flat screen is thick, but the small neck round the back is thin. the pressure is the same, but only when it's a large flat area is there a problem in supporting it.

Some houses may also have vacuum solar collector tubes. These are thin glass and properly evacuated, but because they're only a few inches across they're strong enough. One reason why a practical tube collector can be evacuated and is thus more efficient than a flat plate - which is impractical to evacuate.

[<me9]

There was one available once, which had a slightly undulating finish to the glass, so the high spots touched to take the forces between the panels.

I saw it on TV so it must be true. It was either on Tomorrow's world, or about the end of March.

[<me9]

ITYM implode.

[Andy Dingley]

Or a cold spot, as it's also known. As conductivity of solids is generally higher than gases (depending on how much convective transfer there is) then even a small spot area can be less efficient than a gas fill.

Easiest thing is to fill them gap with aerogel (as used for catching spacedust). This has no mechanical strength so you still need the gas fill, but it cuts out convection currents, thus dramatically reducing the gas' normal heat loss. You lose some visibility too, but it's surprisingly little.

[Dave Stanton]

Same people who use 'oxygen free' cables on their music systems!!!

Dave

[Richard A Downing]

Probably. There is, however, no practical difference. I've seen high-speed films of TV tubes imploding (tests for implosion guards back in the 1960's). The pieces are flung by the inflowing air into the middle, where some hit one another and bounce back, and others just keep on going. The net effect is a violent explosion where bits of glass and the metal bits of the gun are expelled at high speed. The most dangerous bit is the electron gun that usually flies straight out the front where a viewer would be!

One of the reasons for the metal band is to direct any implosion - a bit like a shaped charge for demolition.

HTH, R.

[Mark Carver]

TV sets from the 50s and 60s often had a piece of glass (perhaps perspex ?) in front of the tube, I was always told that was a safety screen in case of implosion, is that true ?

I did come across as a lad in the early 70s a fly tipped TV set, as any bunch of 11 yr olds would we started to rip it apart, I recall that had close fitting perspex around the front of the tube. Anybody know more ? The TV set tipped over, and the tube neck broke off, all there was was a hissing sound for 10-15 seconds as the air rushed in. That by the way is the recommended method to 'defuse' a TV tube, I've done as part of my day job, (wearing goggles and gloves etc, and using a very long broomhandle)

[Richard A Downing]

Yes, that's the 'Implosion Guard' - modern tubes (60's on) have the implosion guard built in, which, together with the tension band, makes them much safer. My father worked on the design of them, and bullet-proof glass, which is why I got to see the films. I'm not an expert really.

Most tubes have a small glass 'pip' on the neck somewhere. It's said to be quite safe to just nip it off with pliers. I don't know if this is true, and like you, I'd only try it with full protective gear on!!!

R.