Barometer repair

[Man On The Clapham Omnibus]

1 hour ago, OldStager said:

Oh, I have no issues at least looking to see what might be wrong with it, but if it is the main spring that would kind of put the brakes on a bit as I don't have any of those fine hair springs, not looked at it yet but I suspect it's the sort of spring that I am not going to have lying around as a spare.

 

Will look later and report back.

If the spring is broken near to the attachment point at one end or the other (very likely) you could simply remove the stub from the anchor point and poke the broken end in instead. It's not like a balance spring where its length is fundamental to the accuracy of the timepiece, it's a return spring in effect and it's natural resonant frequency will be irrelevant.

 

Edit. Oldstager pre-empted my suggestion by saying it's not the spring! That 'spiral tube' is actually a delicate bellows as Ian said. If that is punctured I suspect you're stymied. 

[Richard (OldStager)]

My main issue is where this loose arm goes, as I said there is no witness marks as to where it once sat, but how do I test the bellow tube and what’s in it, guessing mercury but not sure

[Richard (OldStager)]

Yeah the hair spring is fine, it appears to me it’s a needle return / tension spring.

[Richard (OldStager)]

Ok been reading up, seems the bellows is a vessel that has had its air pumped out and sealed, none of the sites mention a vacuum, but to me that’s what it is. Once I figure out where this loose arm goes I can look into it.

[Richard (OldStager)]

I love learning new stuff ( or should that be old stuff !!!)

 

Just found this pic on the net, and my disconnected arm seems to be a multipling lever, doesn't help me find out where it goes yet, but good to know what it's for

 

[Richard (OldStager)]

Wow, think I know where it goes now,thanks to the above diag. Seems my loose soldered at one end arm,attaches to the hair spring, one end of the spring does look like it once had solder on it, but it looks a tad short when offered up to the lever arm.

 

Eta

ok getting there now, I was wrong it’s not the spring it attaches to but a very small chain like wire, as in the diag, it seems it wrapped itself around the mech which is why it was hidden, I have pulled it out and can clearly see where it fastens to the arm.

 

 

Now where is my soldering gear....

[Richard (OldStager)]

I am really struggling to do this on my own, you need 4 pairs of hands.

 

This is where my broken linkage is - marked in red

 

 

The diag appears to show some sort of formed connection, crimped or something, however this is soldered, or was.

The problem is with the link chain moving everywhere and the bar that fastens to it does too, it's a tad hard to keep it all still whilst it's soldered.

[Richard (OldStager)]

And both parts are as thin as small needle for sewing, or a drawing pin.

[Richard (OldStager)]

I don't like being beaten, especially when it comes to mechanical things. An hour of trying to place things still enough to solder and eventually I managed it. It seems to be holding as it's under  a fair bit of tension, I have some very thin oil , so will apply that were I think it needs to be, and then reassemble. Fingers crossed it works now.

 

 

The phone makes it look like it's a huge blob of solder , it's 2mm wide.

[Richard (OldStager)]

All now reassembled and calibrated as best as I could get it, by checking my weather site for my postcode , however I had to convert the metric pressure into imperial. I notice also the pressure isn’t changing much on the website in the coming weeks so it may take a while to prove this works.

 

[Richard (OldStager)]

23 hours ago, Rory's Dad said:

Awaiting a reply too. I also have a dead one acquired under similar circumstances!!

 

 

If you can open it up, to be honest it’s quite a simple device inside. It took me a while to work out what all the parts did, and google helped for images etc.

 

Never done anything like this before, and I have everything crossed that it will be working once the pressure changes.

[Stuart]

@OldStager you can test it by putting it in a sealed bag then applying some gentle pressure to the bag

[Richard (OldStager)]

Funny you should say that I had a similar thought, but I have'nt any bags that would seal well enough , I could do with one of those bags where you use a vacuum to suck air out of when storing clothes, that's the only thing I could think of that would seal well enough.

[IainCameron]

Impressive work, @OldStager!  I think the capsule is naturally 'sprung' into the open position, but it's sealed partially closed so that the partial vacuum holds it mid-way open in mid-range atmospheric pressures.  It's hard to tell from your photo, but if the capsule is 'puffed up'/ expanded, it's likely to be punctured.  We're under relatively high pressure at the moment, so it should be roughly halfway between open and closed (much like your pointer needle).  Clearly, under a massive winter depression the capsule will expand, and under a summer high pressure it will contract.  You could construct a pressure chamber into which you place the barometer, and slowly pump some air into the chamber (or suck it out).  The needle should move accordingly.   Or you can take the easy way out and wait for the weather to change...

[Richard (OldStager)]

Thanks, I will have a think and a good look around the house for something that will be good enough to test it, failing that, as you say I will just have to wait till the weather changes.