Bell Jars Information

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Selecting bell jars

 

Bell jars are a small-sized laboratory apparatus for creating low-quality vacuums. The chambers serve to exhibit individual items, as dust covers, or in combination with other equipment. The conventional shape features a round top and an open bottom. They are manufactured in an array of dimensions and materials.

 

Bell jars consist of amber-transparent cylindrical polyetherimide. The implement is placed open side down on a neoprene gasket on a base plate with a flange. The plate includes tubing adapters for connections to a vacuum pump. The specimen is placed centrally on the base and circular ridges reduce shifting and deformation. Vacuum grease may be used to improve the seal between the bell jar and base. Negative pressure adheres the bell jar to the base. A lift-ring or handle eases bell jar manipulation.

 

Types  

 

Vacuum bell jar: This type is primarily used for low pressure vacuums. A negative pressure force eliminates the need for mechanical assembly. The chambers are suitable for containing below atmospheric pressures.

 

Decorative or preservative bell jar: This product incorporates thin glass and possesses a high degree of clarity. The base flange is delicate, making it unsuitable for use under vacuum conditions. They provide basic protection for fragile and valuable objects that the owner wants to display. Gardeners rely on similar items for guarding plants from damage by frost, insects, and predators.

 

Select stainless steel models engage baseplates, base wells, and feedthrough collars. They often include a viewing window or mechanism.

 

Components

 

  • Feedthrough collars: Access ports connect multiple vacuum parts, including electrical, fluid, and motion feedthrough units. Installing a collar depends on a baseplate as it is situated between the jar and the plate. A stainless steel jar relies on a circular elastomer for establishing a seal between the parts. 
  • Baseplates: The plates are necessary for fixing a jar and the collar. These act as a stable surface for attachment of other components. They are situated over a vacuum pump or a valve fixed to the pump. The devices are available in different diameters. 
  • Base wells: The well is formed when a baseplate is incorporated with a collar. The product substitutes a vacuum seal with a weld joint. The instrument supports multiple access ports that connect with additional systems. These wells integrate with a vacuum pumping system.

Safety

 

Several safety precautions apply when using the instrument, but especially in scientific experimentation. The vacuum chambers are not appropriate for lab work with common organic solvents. Contact with unsaturated or partially halogenated hydrocarbons may lead to immediate failure of the instruments. The equipment must be examined on a frequent basis while in use to identify any clouding, cracks, star formations, or deep scratches. The presence of minor surface scratches and bubbles in the glass is normal.

 

The outer surface must be scrubbed with commercial glass cleaners. Exposure to hydrogen fluoride reacts with the glass and turns it opaque. The surface of the structure is damaged by abrasives, wire brushes, and metal scrapers.

 

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