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A barometer is a working mechanical apparatus. It will perform as well as its design will allow if looked after correctly. Normally barometers require very little attention, but bad repair work can result in poor performance and in extreme cases the devaluation of a valuable item. This mainly effects the case. Ensure that the barometer is kept away from extremes of humidity and temperature, and as dust free as possible. Make sure any fixings and supports are secure. Barometers should not be hung on picture nails but on a securely embedded screw. A barometer falling from the wall will certainly result in breakage and in the case of a mercury barometer there will be problems of containing and disposing of the mercury. It does not need to be hung on an outside wall as pressure does not differentiate between the inside and outside. The recorded temperature will be that of the room.
Aneroid barometers (including barographs) can usually be adjusted by inserting a screwdriver into a hole in the back of the barometer. Care should be taken to ensure that the screwdriver engages with the slot in a small screw buried within the hole. It will usually only need a small fraction of a turn to change the setting of the pointer.
Mercury barometers are more difficult to regulate as it usually means the tube has to be adjusted in the case. In the case of scientific instruments and marine barometers containing mercury, this should only be done by an expert.
When to regulate. This is best done when the weather forecast shows that there is stable air pressure with few variations over the whole country. This will give you a reading for sea level. If you know the height above sea level where you live you can correct for this by decreasing the pressure by 1/10 th inch for every 100 feet above sea level. In practice most domestic barometers are not designed to work at a greater degree of accuracy than this.
Aneroid barometers can be simply but carefully laid flat. The pointers on barographs should be locked (there is usually a lever to do this) and the nib containing the ink carefully removed. Note that the ink will stain so you should ideally wrap in a piece of kitchen towel when handling, empty the reservoir and wash the nib. The nib can then be placed in the cover wrapped in a piece of kitchen towel.
Mercury barometers need to be plugged, unless they are of the enclosed safety (portable) type. To plug the average domestic wheel barometer which has a tube open to the atmosphere you need to carefully take the barometer off the wall and rest it vertically. Ideally with one person should hold it upright open the back door and place a piece of masking tape carefully across the strings that attach the glass floats to the small pulley. Then carefully remove the glass float within the glass tube containing mercury and lean the barometer slowly over by about 45 to 50 degrees. You will see that mercury in the tube will go to the top of the tube. Don’t do this too quickly otherwise you might break the glass tube. Then carefully fit the retaining plug into the open part of the U tube containing the mercury, making sure that the point with the cotton tip is placed firmly into the small opening at the bottom of the wide part of the tube and that the cork sits within the open top of the tube. The glass can be extremely brittle, especially if it's old, so take great care when doing this not to push too hard. Check that the plug is correctly fitted by bringing the barometer upright. The mercury should stay in the top of the tube. If correctly fitted the barometer can be then laid flat. If there is no plug then place a small piece of cotton wool carefully into the top of the tube and keep the barometer at an angle of 45 to 50 degrees. It is possible to carry a barometer around in a car strapped in well to the front passenger seat with the seatbelt, provided this angle is maintained, though it is better if a passenger holds it.
For a stick barometer the procedure is the same except that there are no glass floats. When the barometer is tilted over at about 45 degrees insert the plug as described above. For sealed or portable mercury barometers where there is a leather diaphragm at the bottom of the tube there will be a small screw at the base of the case. When the barometer is tilted over to 45 to 50 degrees carefully screw in the knob to take up the slack in the leather but do not tighten since mercury can be forced through the leather or the leather could be punctured. Check by bringing the barometer upright. There should still be a small gap between the top of the tube and the mercury level. The barometer can then be carefully laid flat. DO NOT allow a removal van to tie an unplugged barometer upright to the side of the van or to be laid flat. This can result in air bubbles getting into the tube and loss of mercury.
Always make sure that a secure fixing is made for the barometer before removing plugs etc. Only remove the plugs when the barometer is at 45 to 50 degrees and then bring the barometer slowly upright before, in the case off a wheel barometer, inserting the floats. Finally carefully remove the tape over the cords taking care not to pull the cords so they come off the grooves in the pulley.
Barometers rarely need attention but should they get dirty they may need cleaning and overhauling. This is a specialist job which City Clocks will be happy to advise you on.
At City Clocks we will be happy to advise you on your Barometer maintenance.
Contact City Clocks here or call us on 0800 78 345 87.