The study of vacuum then lapsed until 1855, when Heinrich Geissler invented the mercury displacement pump and achieved a record vacuum of about 10 Pa ( 0.1 Torr ).
32.
Positive displacement pumps use a mechanism to repeatedly expand a cavity, allow gases to flow in from the chamber, seal off the cavity, and exhaust it to the atmosphere.
33.
:A pump that moves a set volume of fluid through the system for each revolution of the driving shaft . Positive displacement pumps are commonly used in conjunction with highsolids grouting materials.
34.
A positive displacement pump operating against a closed discharge valve continues to produce flow and the pressure in the discharge line increases until the line bursts, the pump is severely damaged, or both.
35.
Positive displacement pumps, however, tend to have sufficiently tight sealing between the moving parts and the casing or housing of the pump that they can be described as " self-priming ".
36.
One modern application of positive displacement pumps is compressed-air-powered double-bunds, to pumping hydrochloric acid from secure storage ( dependent on how the pump is manufactured elastomers / body construction ).
37.
A "'mud motor "'( or drilling motor ) is a progressive cavity positive displacement pump ( PCPD ) placed in the drill string to provide additional power to the bit while drilling.
38.
As with positive displacement pumps, the base pressure will be reached when leakage, outgassing, and backstreaming equal the pump speed, but now minimizing leakage and outgassing to a level comparable to backstreaming becomes much more difficult.
39.
In a typical pumpdown sequence, a positive displacement pump would be used to remove most of the gas from a chamber, starting from atmosphere ( 760 Torr, 101 kPa ) to 25 Torr ( 3 kPa ).
40.
Positive-displacement pumps deliver a nearly fixed volume of air per revolution at all speeds ( minus leakage, which is almost constant at all speeds for a given pressure, thus its importance decreases at higher speeds ).
