A Toepler pump is a form of mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 piston pump

Piston pump

A piston pump is a type of positive displacement pump where the high-pressure seal reciprocates with the piston. Piston pumps can be used to move liquids or compress gases.-Types:* Axial piston pump* Radial piston pump...

, invented by August Toepler

August Toepler

August Joseph Ignaz Toepler was a German physicist known for his experiments in electrostatics. In 1864 he applied Foucault's knife-edge test for telescope mirrors to the analysis of fluid flow and the shock wave. He named this new method schlieren photography, for which he is justifiably famous...

 in 1850.

The principle is illustrated in the diagram. When reservoir G is lowered, bulb B and tube T are filled with gas from the enclosure being evacuated (through tube A). When G is raised, mercury rises in tube F and cuts off the gas in B and T at C. This gas is then forced through the mercury in tube D into the atmosphere. The end of tube D is bent upward at E to facilitate collection of gas (or vapor). By alternately raising G, a pumping action results. Clearly tubes F and D must be long enough to support mercury columns corresponding to atmospheric pressure

Atmospheric pressure

Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

 (76 cm at sea level

Sea level

Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

). Instead of using mercury to provide a valving action at C, it is possible to use a glass float valve.