Brief description

A vacuum pump is a device that removes gas molecules from a sealed volume in order to leave behind a partial vacuum. It was essential for early scientific discoveries regarding air pressure and is critical for creating light bulbs and vacuum tubes.

Use / Function

• Scientific Research: Demonstrating the effects of atmospheric pressure and the properties of a vacuum.
• Manufacturing: Evacuating Incandescent Light Bulb and Vacuum Tube.
• Chemistry: Lowering the boiling point of liquids for low-temperature distillation.
• Food Preservation: Early experiments in vacuum-sealing.

Operating principle

Most early vacuum pumps (like the Sprengel pump or reciprocating pumps) operate on the principle of displacement:

1. Expansion: A chamber’s volume is increased (using a piston or falling liquid), which lowers the pressure inside.
2. Suction: The low pressure draws gas out of the sealed vessel being evacuated.
3. Isolation: A valve or trap prevents the gas from returning to the vessel.
4. Expulsion: The gas is pushed out into the atmosphere, and the cycle repeats.

How to create it

Reciprocating Piston Pump (Guericke style)

1. Cylinder: A precision-bored Metal cylinder.
2. Piston: A piston fitted with a Leather gasket soaked in oil to ensure an airtight seal.
3. Valves: Simple one-way flap valves made of leather or metal.
4. Lever: A wooden handle to provide the mechanical advantage needed to pull the piston against atmospheric pressure.

Mercury Fall Pump (Sprengel Pump)

1. Glass Tube: A long vertical glass tube.
2. Mercury Flow: Mercury is allowed to fall down the tube in drops.
3. Entrapment: Each drop traps a small amount of air from the connected vessel and carries it down the tube, eventually exhausting it at the bottom.

Materials needed

• Essential materials:
  • Metal: For cylinders and pistons (Iron or Brass).
  • Leather: For gaskets and valves.
  • Oil/Grease: For sealing and lubrication.
  • Glass: For the vessels being evacuated and for mercury pump tubes.
• Tools:
  • Lathe: Required for machining a precise cylinder.

Variants and improvements

• Air Pump: The earliest versions, often used for pneumatic experiments.
• Diffusion Pump: Uses high-speed jets of vapor to knock gas molecules out (high vacuum).
• Mechanical Rotary Pump: Modern version using rotating vanes to move air.

Limits and risks

• Leakage: Even the smallest leak makes achieving a vacuum impossible.
• Implosion: Vessels under vacuum can collapse violently if they are not structurally sound.
• Mercury Toxicity: Using mercury pumps involves significant risks of poisoning and environmental contamination.
• Physical Effort: Manually pumping a large volume is extremely labor-intensive.