Vacuum pump

A vacuum pump is a specialized device used to remove gas particles from a sealed volume. By evacuating these particles, the pump creates a partial vacuum, which is a space with much lower pressure than the atmosphere. These devices are essential for scientific research and industrial processes. They allow us to study how matter behaves in environments with very few molecules.

Vacuum pumps operate through three primary scientific techniques: positive displacement, momentum transfer, and entrapment. Positive displacement pumps work by repeatedly expanding a small, sealed cavity. As the cavity expands, the pressure drops, allowing gas to flow in from the main chamber. The pump then seals the cavity and shrinks it to exhaust the gas into the atmosphere.

This method is highly effective for creating low vacuums. Common examples include the piston pump, the rotary vane pump, and the scroll pump.

Momentum transfer pumps, also called molecular pumps, function differently. These are used when the pressure is already quite low, typically below 0.1 kPa. At these low pressures, gas molecules do not bump into each other as much as they do at normal atmospheric pressure. Instead, they interact more frequently with the walls of the chamber. Momentum transfer pumps use high-speed rotating blades or jets of dense fluid to knock these molecules toward the exhaust.

There are two main types: the diffusion pump, which uses jets of oil or mercury vapor, and the turbomolecular pump, which uses high-speed fans. Because these pumps lack a physical seal, they often require a positive displacement "backing pump" to prevent air from leaking back into the system.

The third technique is entrapment. Entrapment pumps do not push the gas out of the system. Instead, they capture gas molecules and hold them in a solid or adsorbed state. One example is the cryopump, which uses extremely cold temperatures to condense gases into solids. Another is the ion pump, which uses strong electrical fields to move ions onto a solid surface. These pumps are used to reach ultrahigh vacuums, though they eventually need to be regenerated to clear the trapped particles.

The history of vacuum technology began long before the modern pump was invented. Suction pumps have been used since antiquity, and the Arab engineer Al-Jazari described dual-action suction pumps in the 13th century. By the 17th century, scientists began to study the limits of suction. In 1638, Galileo Galilei suggested that water columns in pumps would break under their own weight at 34 feet. While his specific math was incorrect, his work led to major discoveries. In 1643, Evangelista Torricelli built the first mercury barometer and proved that the space at the top was a vacuum.

In 1650, Otto von Guericke invented the first true vacuum pump. He famously demonstrated the power of atmospheric pressure using the Magdeburg hemispheres experiment. He showed that even teams of horses could not pull apart two metal hemispheres when the air had been evacuated from between them. Later, Robert Boyle and Robert Hooke improved these designs to study the properties of a vacuum more closely. By 1855, Heinrich Geissler invented the mercury displacement pump, reaching a record vacuum of 10 Pa.

Today, different pumps are chosen based on specific technical needs. For instance, a Roots blower is used when very high pumping speeds are required, though it has a low compression ratio.

In semiconductor manufacturing, regenerative pumps are used in load locks because they offer high pumping rates and low contamination. Engineers must consider many factors when selecting a pump, such as manufacturing tolerances, reliability, and tolerance to dust or chemicals. Understanding these mechanisms allows us to manipulate the physical world at a molecular level.