The Neon Bender's BBS!

The Archive no longer allows posting but search of hundreds of previous posts are available
If you have any questions please contact us.

[Please Read]

[ View Thread ] [ Return to Search ] [ Read Prev Msg ] [ Read Next Msg ]

Re: HELP!!! I Screwed-UP

Posted By: SVP Neon Equipment
Date: Saturday, 30 December 2006, at 1:39 p.m.

In Response To: Re: HELP!!! I Screwed-UP (John Anderson)

> As is common in a busy neon shop after a
> long day. Mistakes DO happen. A safety
> ground path helps minimize the damage when
> they do IMO.

Or, it could cause more problems than it solves - IMO.

> Your gauge fried because is has a ground
> potential through which the dischage
> completed its path.

Not necessarily so. Apparently you either didn't believe what I said about high voltage following more than one ground path simultaneously or you just ignored it. As I have already stated, a grounded gauge tube would not have necessarily stopped it from damaging the gauge itself.

> Electriacally isolated, battery powered gauges will help - but still
> have a small amount of ground-potential. I
> feel an earth-grounded gauge tube provides
> more reliable protection.

I will agree that a grounded gauge tube is a reliable method of attracting the high voltage discharge. I disagree with the "protection" part.

> I have seen both
> bombarder flashbacks and spark-coil
> dischages safely dissapate though a grounded
> gauge tube.

And I have seen just the opposite - gauges and tubes destroyed because the gauge tube was "properly grounded".

> Unless you are going to enclose your entire
> system and gauges in a vacuum or
> dielectric-oil - you can't escape capcitive
> coupling to ground. That's why a neon tube
> still flickers if you remove one electrode
> wire.

Huh???

> You can also inadvertantly become the
> ground path yourself by touching a metal
> Robbins valve, gauge tube, or other
> conductive part (of your glass manifold) -
> with dangerous consequences.

Agreed. But IMO having ground paths within the manifold only increases the chances of this happening, not decrease them. Why? Because that flashback may go to more than one ground potential at the same time and one of those ground potentials may be the operator.

> Everyone has to adjust the pressure to the
> 'trode manufacturers recommended level while
> processing (usually around 1 torr).

We recommend 2 to 5 Torr for heating the glass. 1 is too low for this purpose and may even be too low to heat the electrodes without undue sputtering. But that's another subject...

> Sure, you can repeatedly cut the bombarder on and
> off as you do this... but IMO that's a lot
> of trouble and it slows down the pumping
> process.

A very interesting comment. Turning the bombarder on and off to adjust the pressure is by far the safest way to do it to prevent a potential flashback. Doing the opposite is UNsafe. But that does explain why you didn't comment on my mention of a redundant momentary switch. Those extra couple of seconds to be on the safe side really add up after a while...

> We never do that here - bombarding
> contuniues while we momentarily open the
> stopcock to maintain the proper pressure.

An extra couple of seconds... Actually, not even. If the operator is on their toes we are talking no more than 1 second to turn the bombarder off, adjust the pressure and turn it back on again.

> Flash back only occurs if something goes
> wrong, like the pressure gets too high or
> too low by lapse of attention.

If someone is having a lapse of attention while bombarding it is time to stop. When I have seen my people look like they are not paying 100% attention to what they are doing I make them take a break. I have done it myself more than once and will do it again if and when necessary. With even a moderate size bombarder it only takes one mistake. Lapse of attention? Time to quit!

> In these cases, it is safely carried off to ground.
> This very, very rarely happens. But when it
> does - I'm sure glad the ground path is
> there. So are the sensitive electronics
> peppering my manifold.

Or if that person who is tired and having a lapse of attention and is leaning against the manifold (touching it) when something goes wrong they may be enough of a ground potential too.

> If you have problems with a ground path in
> the manifold - it means the path of
> resistance is less the bombarder pole to the
> ground than it is inside the tube. This
> shouldn't be - even with a mid-point
> grounded pole pig. Pressure is too low or
> too high. Or, the grounding electrode is too
> close to the tube.

Sorry, I am not following what you are saying.

> I think an ideal place
> for the safety ground is after the
> tubulation glass (going toward the
> manifold), where the manifold is back to
> large diameter tubing and before any gauges
> or stopcocks. You can also reduce the
> tendency to flashback by removing the
> emission coating from this electrode - or,
> as I now do just have a small dumet wire
> hang down.

Why not just add 2 ft. of tubulation to the end of the manifold? j/k I've seen this attempted too. But with a well grounded manifold the bombarder even over came this to go through the tubulation to ground instead of just lighting up the tube.

> I don't think anyone here wants to see two
> people duke it out over 180-degree opinions
> on grounding electrodes.

Hmm, I didn't know we were duking it out. I thought we were just having a discussion on the subject and that was what these forums were for?

> There are many shops all over the world making quality neon
> using both methods. I'll happily discuss it
> further with anyone off-line - but I've
> already said more than I intended in this
> long thread. This is my last post on it.

Certainly if anyone feels like contacting you directly to discuss this I encourage them to do so. But I fail to see how a private discussion on the subject, which would unquestionably be one-sided, could be as beneficial to the industry as a whole as an open forum discussion would be. But again, that's JMO.

> Peace to all - and I wish everyone a
> prosperous 2007

Thank you, John. That is my desire as well, to see the industry prosper!

SVP Neon Equipment

Messages In This Thread

[ View Thread ] [ Return to Search ] [ Read Prev Msg ] [ Read Next Msg ]

Neon Bender's BBS! is maintained by Kenny with WebBBS 5.12.

This page Copyright © 1996-2005 Krypton Neon