Barometer Dismantling

[thescullster]

Hi all

Back again with the old baro!

So I decided to take a peak last night to see if the chain was crudded
up or the bellows unit shot.
But fell at the (almost) first hurdle.
Unscrewed three screws around the glass perimeter expecting the whole
gubbins to lift out but no, just the glass lifts away and the dial etc
remains housed in the wood casing.
Unscrewed the screws around the dial, but that is held captive by the
needle.

So, how do I remove the needle - it appears to be kind of riveted to the
shaft end?

Before and after investigations, when the glass is tapped the needle
moves 3-5mm. The needle seems fairly free to rotate, so presumably the
chain gubbins is likely to be OK, but the bellows not? I have not seen
the needle move more than an inch or so in either direction (from the 12
o'clock position).

I guess if I can get the needle off without damaging the internals, all
will be revealed.

Thanks

Phil

[newshound]

Clock hands are normally "push fit" on the spindle but can get very
tight. Like you, I think I'd expect the whole assembly to come out. Is
it held in from the back?

[Arfa Daily]

"thescullster" <thescu...@dropthespam.com> wrote in message
news:3eOdnQ5tHLk5o1DM...@eclipse.net.uk...

You may not have left it long enough. The pressure has barely moved here for
several days. I have both my aneroid and my electronic barometers set for
'local' pressure. Yesterday, both were pretty steady at around 1012 mbars.
This morning, they have both dropped around 5 points. That's about a quarter
inch on the aneroid dial.

If you look at a current synoptic chart such as

http://www.metoffice.gov.uk/weather/uk/surface_pressure.html

you will see that there are high(ish) pressure systems to the east and south
and south of us. To the west is a large full blown high. They are all big
systems and will not be easily dislodged over - I would guess - at least the
next few days, but you might well see that system out to the west nudging in
over the weekend, clearing the skies, and driving your barometer up a few
points. Although weather systems are quite dynamic, and those that grace us
with their presence are more active than a lot due to the fact that we are
sandwiched between large ocean and land masses, you should not get fooled
into thinking that your barometer will dance up and down on a daily basis.
At the height of summer and winter, we can get pressure systems that are
static for days - or even weeks - at a time. The time to watch your
barometer is when there are storms about. As the leading edges of frontal
systems come across, you can sometimes watch the pressure drop like a stone
over hours, or sometimes even minutes. Try having a look next time you get a
sudden wind (blowing along a front) before a sudden 'stop' (the calm before
the storm) followed by the rain hanging on the back edge of the front,
before the storm passes. If you plot the readings, you will see a short
sharp drop in the pressure, before it levels out for a short time, followed
by it climbing back to around the previous level.

Do you have an airfield nearby, and any kind of radio that you can listen to
its arrivals / departures controller on ? Every pilot is given an accurate
barometer setting for either 'local' ("QFE" ) or regional ("QNH") pressure
to set their altimeter to, depending on whether they are taking off /
landing, or just 'passing through' that airfield's control zone. This is
done to make sure that everyone in the control zone is flying 'on the same
page' height-wise and that altimeters read zero on the ground, and also that
they register the same height as everyone else when they leave the control
zone and join others already on a different page.

Their barometers are high quality and certified, so it is a good resource
for checking and calibrating your own against. Personally, I would wait at
least a week and refer regularly to synoptic charts for the UK before
declaring your barometer 'faulty' and trying to tear it down just to 'have a
look'. They are quite delicate, and you might finish up wrecking a perfectly
good instrument ... :-(

Arfa

[Nightjar]

On 28/06/2013 08:43, thescullster wrote:

> Hi all
>
> Back again with the old baro!
>
> So I decided to take a peak last night to see if the chain was crudded
> up or the bellows unit shot.
> But fell at the (almost) first hurdle.
> Unscrewed three screws around the glass perimeter expecting the whole
> gubbins to lift out but no, just the glass lifts away and the dial etc
> remains housed in the wood casing.
> Unscrewed the screws around the dial, but that is held captive by the
> needle.
>
> So, how do I remove the needle - it appears to be kind of riveted to the
> shaft end?

It is probably a push fit, like a clock hand. There are special tools
for taking clock hands off:

http://www.ebay.co.uk/itm/Clock-Hands-Removal-Tool-/400501158247

A pair of end cutters can be used, with care, instead.

> Before and after investigations, when the glass is tapped the needle
> moves 3-5mm. The needle seems fairly free to rotate, so presumably the
> chain gubbins is likely to be OK, but the bellows not? I have not seen
> the needle move more than an inch or so in either direction (from the 12
> o'clock position).

Which could simply be an indication of a stable pressure system in the area.

> I guess if I can get the needle off without damaging the internals, all
> will be revealed.

Except where that little part that fell off and rolled away went. :-)

Colin Bignell

[The Natural Philosopher]

On 28/06/13 09:46, Nightjar wrote:
> On 28/06/2013 08:43, thescullster wrote:
>> Hi all
>>
>> Back again with the old baro!
>>
>> So I decided to take a peak last night to see if the chain was crudded
>> up or the bellows unit shot.
>> But fell at the (almost) first hurdle.
>> Unscrewed three screws around the glass perimeter expecting the whole
>> gubbins to lift out but no, just the glass lifts away and the dial etc
>> remains housed in the wood casing.
>> Unscrewed the screws around the dial, but that is held captive by the
>> needle.
>>
>> So, how do I remove the needle - it appears to be kind of riveted to the
>> shaft end?
>
> It is probably a push fit, like a clock hand. There are special tools
> for taking clock hands off:
>
> http://www.ebay.co.uk/itm/Clock-Hands-Removal-Tool-/400501158247
>
> A pair of end cutters can be used, with care, instead.
>

I went in from the back I think

>> Before and after investigations, when the glass is tapped the needle
>> moves 3-5mm. The needle seems fairly free to rotate, so presumably the
>> chain gubbins is likely to be OK, but the bellows not? I have not seen
>> the needle move more than an inch or so in either direction (from the 12
>> o'clock position).
>
> Which could simply be an indication of a stable pressure system in the
> area.
>
>> I guess if I can get the needle off without damaging the internals, all
>> will be revealed.
>
> Except where that little part that fell off and rolled away went. :-)
>

yes. I am worried about taking the needle off..

> Colin Bignell


--
Ineptocracy

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[Nightjar]

On 28/06/2013 09:50, The Natural Philosopher wrote:
...

> yes. I am worried about taking the needle off..

Also, how would you know where to align it when putting it back, unless
you had another barometer to work from?

Colin Bignell

[thescullster]

Hi newshound

No there is no back access except for a small hole to an adjusting screw.
The way the glass and dial are fixed the internals are clearly accessed
from the front only.

Phil

[thescullster]

Hi Arfa

Thanks for comprehensive response.
I appreciate what you are saying about the reading remaining static for
a period. What I didn't make clear is that this baro has hung on my
parents' hallway wall for years and I've never seen a significant shift
on the needle - maybe an inch max!

Phil

[John]

"thescullster" <thescu...@dropthespam.com> wrote in message
news:3eOdnQ5tHLk5o1DM...@eclipse.net.uk...

> Hi all
>
> Back again with the old baro!
>
>

> Before and after investigations, when the glass is tapped the needle moves
> 3-5mm. The needle seems fairly free to rotate, so presumably the chain
> gubbins is likely to be OK, but the bellows not? I have not seen the
> needle move more than an inch or so in either direction (from the 12
> o'clock position).

Two quick ways to test the diaphragm (discovered by accident):

1. Put barometer in car with windows, vents and all doors except one
closed. Slam remaining car door. Needle should jump 1/2" or so.

2. Find local big hill and drive up and down, checking change in barometer
reading. Can't remember what the rate of change is for inches of mercury
in this metric era, but it should be noticeable in 200 feet change of
elevation.
NB. Doesn't work in E. Anglia as there aren't any hills.


rusty

[news]

On 28/06/2013 10:52, John wrote:

>
> 2. Find local big hill and drive up and down, checking change in barometer
> reading. Can't remember what the rate of change is for inches of mercury
> in this metric era, but it should be noticeable in 200 feet change of
> elevation.
>
>

> rusty
>
>

At sea level is is approximately 3mb/100 ft which if my calcs are
correct its 0.1inHg per 100ft.

--
Chris

[The Natural Philosopher]

That's easy. go to nearest RAF weather station.

1018.85 mb at Lakenheath right now
Cambridge showing 1020 give or take.

This is fairly useful also

http://www.eldoradocountyweather.com/forecast/UK-Ireland-Currents/uk-current-barometric-pressure.html

[Brian Gaff]

If it has actually moved then surely the bellows must be working. Tapping is
often needed on these things to make them move as I'm sure you are aware.
The original touch sensitive devices!
You need another one to see if the readings agree, as pressure has been not
hugely different in the last few days or so.
You can hear the pressures on forecasts or on the web. I have an air band
radio so being near an airport I can tune in to the volme, and there you can
get your elevation to set the offset of courset.
Brian

--
From the Sofa of Brian Gaff Reply address is active

"thescullster" <thescu...@dropthespam.com> wrote in message

news:fvSdne03UJVwyVDM...@eclipse.net.uk...

[Brian Gaff]

You can get your ears to pop even going up and down the southa nd north
downs so it has to be fairly substantial.

Brian

--
From the Sofa of Brian Gaff Reply address is active

"news" <ne...@news.salis2.co.uk> wrote in message
news:godzt.10559$bC2...@fx03.fr7...

[Steve Firth]

news <ne...@news.salis2.co.uk> wrote:

> At sea level is is approximately 3mb/100 ft which if my calcs are correct
> its 0.1inHg per 100ft.

Err 100ft isn't sea level, HTH.

--
<•DarWin><|
_/ _/

[Dave Liquorice]

On Fri, 28 Jun 2013 10:13:31 +0100, Nightjar wrote:

> Also, how would you know where to align it when putting it back, unless
> you had another barometer to work from?

Not overly important provided you get it fairly close. The altitude
adjustment ought to cope with a good 100 mb (3" Hg).

--
Cheers
Dave.

[Dave Liquorice]

On Fri, 28 Jun 2013 12:04:14 +0100, Brian Gaff wrote:

> You can get your ears to pop even going up and down the southa nd north
> downs so it has to be fairly substantial.

I think that depends on how often you go up and down hills. My ears
don't pop when going from near sea level up to 2,000' down to 1,000
and then back up to 1,400' at home.

My AWS barometer has 57 mb of correction, or 4 mb per 100' close
enough to the previosly quoted 3 mb per 100' as it's non linear. 3 mb
is 0.088" Hg, 4 mb 0.118" Hg.

--
Cheers
Dave.

[polygonum]

I think it depends on health.

A few years ago I was finding somewhere around 200 feet could be
uncomfortable - now back as I always was, several hundred feet and I
don't notice at all most of the time.

Amazing what the right medicine does.

--
Rod

[Arfa Daily]

"news" <ne...@news.salis2.co.uk> wrote in message
news:godzt.10559$bC2...@fx03.fr7...

That's about right. My local airfield is about 300 ft ASL, and they call 9
or 10 points of difference between the QNH and the QFE

Arfa

[Arfa Daily]

"polygonum" <rmoud...@vrod.co.uk> wrote in message
news:b35ijq...@mid.individual.net...

I think it depends on speed as well. In theory, your ears shouldn't pop at
all if your eustachion tubes are clear, but maybe as you get older, they
clog up, and the pressure equalisation doesn't take place as quickly. I have
been in lifts that go up a long way, and had no problems, but in America,
some of the lifts are very fast, and I tend to get ear popping on them.

Arfa

[polygonum]

On 28/06/2013 18:06, Arfa Daily wrote:
> I think it depends on speed as well. In theory, your ears shouldn't pop
> at all if your eustachion tubes are clear, but maybe as you get older,
> they clog up, and the pressure equalisation doesn't take place as
> quickly. I have been in lifts that go up a long way, and had no
> problems, but in America, some of the lifts are very fast, and I tend to
> get ear popping on them.
>
> Arfa

You are, IMHO, quite right about speed. Makes all the difference.
Suspect that if it is slow enough the ordinary way we swallow from time
to time is enough.

It was quite possibly the very first symptom of my deterioration about 6
or so years ago. And very glad I am not to have it any more. Living in a
hilly location, I'd find even very local trips could be unpleasant at times.

--
Rod

[Chris J Dixon]

polygonum wrote:
>
>You are, IMHO, quite right about speed. Makes all the difference.
>Suspect that if it is slow enough the ordinary way we swallow from time
>to time is enough.
>

Reminds me of the time I had a flight in a Short 330, which had
the feel of being little more than a Leyland National with wings.

Boiled sweets were handed round before take-off and landing,
intended to promote swallowing and hence ease the discomfort on
our ears. Being unpressurised they couldn't gain much height to
get above the weather.

The interior trim panels were covered with sticky-backed plastic,
and, as the plane gained height, little bubbles appeared as it
lifted off the backing. On descent, it all shrank back again.

It amused me that the flight deck was so small that each pilot
had his own sliding door, through which his in-flight cuppa was
duly passed.

Chris
--
Chris J Dixon Nottingham UK
ch...@cdixon.me.uk

Plant amazing Acers.

[hamilt...@gmail.com]

[Brian Gaff (Sofa 2)]

2013?
where did that come from?
Brian

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[Andrew]

Jet Stream ?, piggybacked on Storm Dennis ?