[PSUBS-MAILIST] Gauges and vacuum

[Stephen Fordyce via Personal_Submersibles]

Hi Brian,
I recently went through an evaluation of some gauges I got - it was rather
fun destroying them and a photo of the ruined internals is here:
https://www.facebook.com/tfmengineeringaust/photos/pcb.777589079041244/777589062374579/?type=3&theatre
<https://www.facebook.com/tfmengineeringaust/photos/pcb.777589079041244/777589062374579/?type=3&theater>

The bourdon tube flexes slightly with pressure and drives a rack and pinion
mechanism that turns the needle.

>From a pressure perspective nothing catastrophically dangerous should
happen (although make sure the case of any gauges can equalise with vacuum
around it) but if you have a vacuum in the process bit of the gauge
and 1atm in the case, the needle will try to go below the zero
reading point and possibly mess up the zero point because the needle will
be pushed against the zero point stopper quite hard.

Easy ways to prevent this could include:
1. Make sure the pressure in the process connection and the case of the
gauge are the same (ie. open the case and the process connection so they
both see vacuum)
2. Keep the pressure in the process connection above the case pressure
(ie. by locking some gas in or keeping open to 1atm outside the sub while
you pull vacuum on it)

Cheers,
Steve

On Mon, Jan 25, 2016 at 4:59 PM, Brian Cox via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Would anyone know if having a pressure gauge or a sea-water depth gauge in
> a vacuum environment could adversely affect the gauge?   Since I'm not to
> savy with the internal workings of analog pressure gauges I thought I might
> ask the group.  I'm about to pull a vacuum on my pressure hull and the
> thought occurred to me.
>
> Brian Cox
>
>
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.whoweb.com/pipermail/personal_submersibles/attachments/20160125/aeeb04a5/attachment-0001.html>