Tapping barometers

Well, I've always bashed the hull out of barometers to see the trend. ASFAIK this is the only way to do so with a Dial barometer...

But I am no doubt very very wrong as somebody is going to tell us very soon....

<hr width=100% size=1><A target="_blank" HREF=http://www.ybw.com/cgi-bin/forums/postlist.pl?Cat=&Board=wanted>Stuff Wanted </A>
 
Tapping is OK if it is a tap and not a wallop and the tapping is done to the case and not the glass face. That does not shatter so easily

<hr width=100% size=1>
 
As an eminent admiral; whose name escapes me,said "If barometers needed tapping they would be supplied with a hammer".
If you tap a barometer and the needle jumps significantly it needs servicing.

<hr width=100% size=1>If it can't be fixed with a lump hammer dont fit it!
 
Tapping is OK if it is a tap and not a wallop and the tapping is done to the case and not the glass face. That does not shatter so easily. There! That's told you!

<hr width=100% size=1>
 
No need to tap mine, it's electronic!

I always had to tap my old (aneroid) one. I had reservations about getting an electronic one, but it is excellent. The chart to show the trend is very useful indeed.

Joe


<hr width=100% size=1>
 
Only the owner is allowed to tap it - otherwise you don't know when it was last tapped and how much and which way it moved since you last tapped it.

I just wish I could stop my kids tapping mine!

<hr width=100% size=1>my opinion is complete rubbish, probably.
 
Hi!

I'm exactly the same and never tap the barometer (was told NEVER to do so by the ex big ships captain who taught me for me my RYA Offshore 25 years ago) and find it moves perfectly well on its own. As baro readings are recorded hourly in the log, any trend is obvious.

Good sailing!



<hr width=100% size=1>
 
Well, if you find that the barometer moves when you tap it, then it needs to be tapped to overcome "stiction" - good word!

I was always told that you should never tap someone else's barometer. Bit rude, like coming aboard without asking first.

<hr width=100% size=1>
 
As an instructor teaching about barometers and altimeters (essentially barometers with a large range of readings and an adjustable datum), I can see both sides to this arguement.

The Admiral referred to earlier is right to some extent, that a well crafted mechanical barometer will require minimal "percusive adjustment" as it will be as frictionless as is possible. Tapping, even light tapping, will damage the bearings and linkages of such an instrument over a long period. Heavy tapping obviously will hasten that damage! The bearings in a good instrument are ruby("real" or manufactured) and very sharp, iridium tipped pivots. These pivots will chip at the ruby, and wear down quicker with impacts, increasing the friction they were designed to minimise.

The converse is that even the best made instruments will have some friction in the linkages to over come, as well as hysteresis (the capsule will not return to exactly the same size if pressure is changed away from and then returned to a set pressure) in the capsule itself. Tapping reduces the friction temporarily (coefficient of moving friction being less than static friction), so allowing the instrument to indicate the pressure more accurately.

So you pay your money and make your choice. Tap, get an accurate reading at the expense of slowly damaging your instrument and making tapping more necessary. Do not tap, get a slightly less accurate reading (maybe half a millibar/hectopascal out), but have the instrument maintain this accuracy for longer.

Tapping the glass is definitely discouraged. Not only do you risk breaking the glass, in some instruments you can end up pushing the glass so it touches the spindle of the indicator needle. This obviously retards or even completely stops it moving.

Personally, while I do not get sanctimonious about it, I am not a "tapper" of barometers, as they are precision instruments! Altimeters on aircraft are more rough and ready. Modern ones use electrical ones that are virtually frictionless. Older, smaller aircraft have mechanical ones. They are actually fitted with a small motor and weight that your can hear ticking about 5 times a second, hitting the frame of the instrument to obviate the need to tap. An automatic tapping device. The wear and tear is just accepted.

<hr width=100% size=1>You can lead a student to knowledge, but you cannot make them think.
 
I can't imagine why there's no law against this, with regular inspections by qualified people that will impose fines or, if found to be a tapper of the heavier variety, have one's boat impounded.
While they're about it they could check for untidy lockers, frayed ends on warps, slightly loose guard rails, etc

<hr width=100% size=1><font color=blue>Mark
 
I was told you should have two barometers: One in the main saloon for the crew to thump, and one in the skipper's cabin for the purposes of ascertaining the atmospheric pressure.

<hr width=100% size=1>
 
What you have declined to say is that this particular barometer is on a very expensive Najad!! I wonder if it was situated on an old Westerley Centauer ( sorry if that causes offence) the procedure would be diffearnt....any way the particular crew concerned ( god bless him)is now busy tapping a very expensive anchor winch that seems not to be playing the game!

<hr width=100% size=1>
 
I find this thread utterly baffling, but it may reflect just how utterly out of touch I am.

One of the beauties of analogue instruments, eg clocks, is that they show you more information than the digital version.

A barometer is for tapping. You tap the glass, gently, with finesse, as you would when dealing with any piece fo precision engineering. My Negretti and Zambra Fisherman's Aneroid has been in the family for at least 40 years, still works perfectly and gives identical readings when put alongside a more modern instrument, and must have had its glass tapped several thousand times without ill effect.

The beauty of all this is that no-one really needs to know the pressure; the direction and rate of change are THE parameters that are significant. I have another useful aneroid that has two sets of legends for rising and falling and thus gives just about all you need to know about weather trends straight off the dial.

Sure, most barometers have a second adjustable needle that shows where the main needle was yesterday or this morning, but nothing will show you what's happened in the last hour or two as well as a gentle tap. I'm sorry, ladies and gentlemen, but this "you should NEVER tap a barometer" is missing the point. It's the barometer's secret message that those not in the know don't understand how to extract!

Regards, Mudhook.

<hr width=100% size=1>
 
You must log in or register to reply here.

Other threads that may be of interest

O
“The Dog that Didn’t Bark:” Yanmar. 4L HASTE.
Replies
2
Views
262
oldgit
O

Share this page

Top