Laboratory vacuum chambers: for which applications is a controlled vacuum volume required?

The vacuum bell jar creates, in seconds, a sealed volume when coupled to a vacuum pump for degassing, gentle drying, leak testing or the temporary protection of samples. Available in polycarbonate (high impact resistance), borosilicate glass (excellent chemical compatibility) or acrylic, they can be supplied with stopcock, vacuum gauge, O-ring and grooved base plate. A nimble alternative to heavy vacuum chambers, the bell jar is ideal for routine work in chemistry, materials, quality control and teaching.

What types of vacuum bell jars are there, and how do you choose the right one?

A vacuum bell jar combines a clear dome, a flat base (anodised aluminium, filled polymer or glass), an O-ring (NBR, silicone, Viton) and, depending on the model, a tap and a vacuum gauge. Selection is driven primarily by the material, the useable volume, the allowable vacuum level and the chemical compatibility.

On performance, bell jars cover the rough/primary vacuum range (with diaphragm or rotary vane pumps) for degassing and room-temperature drying. Key accessories: grooved platform (vessel stability), 1/4 tap with hose barb, vacuum gauge (-1 to 0 bar), quick vent, desiccant tray.

Selection criteria:
• Application (resin degassing, leak testing, drying) and required vacuum level.
• Chemical compatibility (solvents) and safety (impact resistance, protective shield for routine work).
• Volume and footprint, ergonomics (handles, weight), maintenance (cleaning, O-ring replacement).

Good practice: always check the model’s ultimate pressure, inspect the dome for crazing/micro-cracks, keep the O-ring clean and lubricated, and use a safety screen during vacuum trials.

What are the main applications for a vacuum bell jar?

Versatile, the vacuum bell jar proves its worth in many situations where a fast, controlled and visible vacuum is needed:
• Chemistry and materials: degassing resins, polymers, inks and gels before casting or polymerisation; room temperature drying of moisture-sensitive powders.
• Quality control (food, pharma, cosmetics): qualitative leak testing on small packages and closures; observing bubble formation under vacuum in a suitable bath.
• R&D and prototyping: removing microbubbles from silicones, adhesives and analytical mixtures; preparing bubble-free samples for measurement.
• Life sciences: preparing gels or hydrogels without bubbles and gently drying heat-sensitive samples at ambient temperature (with desiccant if required).
• Education: demonstrations of atmospheric pressure, cold boiling, and sound propagation in low-pressure air.

According to your application, choose the material (PC, glass, PMMA), volume and fittings (stopcock, gauge) to achieve a repeatable vacuum safely.

The different types of vacuum bell jars available

Frequently asked questions about vacuum bell jars

What’s the difference between a vacuum bell jar and a vacuum desiccator?
The bell jar sits over a smooth baseplate and is ideal for quick manipulations. The desiccator includes a flange/shelf for desiccant, designed for drying and dry storage.

How low a vacuum can I go?
Depending on the model, typically the rough vacuum range. Refer to the maximum allowable pressure rating and watch the vacuum gauge. Never exceed the manufacturer’s limits.

Which vacuum pump should I use?
Use a diaphragm pump for clean/aqueous applications; a rotary vane pump for deeper vacuum. Connect via the stopcock and suitable vacuum hose, with a non-return (check) valve if required.

Can you heat under a bell jar?
Bell jars are intended for ambient temperature use. Avoid hotplates and thermal gradients. For hot drying, use a specified vacuum oven/chamber.

Is a polycarbonate bell jar autoclavable?
Often not recommended. Heat and pressure can introduce stress. Prefer gentle chemical disinfection. Always check the manufacturer’s instructions.

What safety precautions should I take?
Inspect the dome and the seal, avoid solvents that cause stress crazing in PC/PMMA, use a safety shield, and do not leave the bell jar under vacuum unattended for extended periods.