Chapter 2 — PRESSURE 



1. Glass tube. 



2. Brass casing. 



3. Leather joint. 



4. Top flange. 



5. Flanged cylinder. 



6. Leather gasket. 



7. Ivory point. 



8. Glass cylinder. 



9. Mercury. 



10. Long screws. 



11. Leather gaskets. 



12. Lower flange. 



vita i^# 



' B IP 



13. Upper curved 

 cylinder. 



14. Split-ring clamp. 



15. Leather gasket. 



16. Lower curved 

 cylinder. 



17. Wooden bearing. 



18. Leather bag. 



19. Cistern housing. 



20. Screwcap. 



21. Adjusting screw. 



the back. With the cover open, the barometer 

 is completely exposed, so that all parts are 

 accessible and adjustments can be made easily. 

 A metal hanger inside the case near the top 

 and a centering ring near the bottom provide 

 means for suspending the barometer. Two 

 openings in the back of the case are fitted with 

 white opal glass or heavily pigmented white 

 Plexiglas to facilitate reading the scales and 

 observing the cistern level. Two brackets are 

 provided for mounting the case on a wall, 

 post, or other suitable vertical surfaces. 



SCALES.— The Fortin barometer has two 

 scales. One is the stationary scale, which allows 

 reading of the barometer to the nearest 0.05 

 of an inch (also graduated in millibars, but 

 not read). The other is an adjustable scale, called 

 the vernier, which is graduated to allow reading 

 the barometer without interpolation to the near- 

 est 0.002 of an inch. 



Maintenance 



Preventive maintenance for the Fortin barom- 

 eter consists largely of cleaning, minor adjust- 

 ments, and daily inspections. These inspections 

 include checking for cracks in the glass tube 

 or cylinder; damage to the wooden case; loose 

 screws in the case brackets, hanger, and centering 

 ring of the case; and condition of the mercury 

 column. If a cracked tube, a mercury leakage, 

 or other damage that may affect the accuracy 

 of the instrument is discovered, it becomes 

 necessary to request a replacement barometer 

 and to ship the defective barometer to NAS, 

 Norfolk or NAS, Alameda for overhaul. 



The barometer and case should be kept 

 clean by wiping with a soft, clean cloth. Occasion- 

 ally, the scales may be wiped clean and a thin 

 coat of high-grade clock or instrument oil applied. 

 Do not use a commercial polish on the scales 

 or use heavy pressure when wiping them. 



The Aerographer's Mate may change broken 

 thermometers and repair damage to the wooden 

 case. For complete information on the main- 

 tenance of the ML-512/GM, refer to NW 50- 

 30ML512-1. 



209.98 

 Figure 2-5.— Exterior and cross section view of 

 a Fortin barometer cistern. 



ANEROID BAROMETERS 



Mercurial barometers are quite accurate, 

 but they are expensive and are not easily trans- 

 ported. For numerous practical purposes they 

 are replaced «or supplemented by a mechanical 



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