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Roots bloweralso called a booster pump, has highest pumping speeds but low compression ratio Multistage Roots pump that combine several stages providing high pumping speed with better compression ratio Lobe pump The base pressure of a rubber - and plastic -sealed piston pump system is typically 1 to 50 kPa, while a scroll pump might reach 10 Pa when new and high vacuum pump rotary vane oil pump with a clean and empty metallic chamber can easily achieve 0.
A positive displacement vacuum pump moves the same volume of gas with each cycle, so its pumping speed is constant unless it is overcome by backstreaming.
Momentum transfer pump[ edit ] A cutaway view of a turbomolecular high vacuum pump In a momentum transfer pump, gas molecules are accelerated from the vacuum side to the exhaust side which is usually maintained at a reduced pressure by a positive displacement pump.
Vacuum pump - Wikipedia
Momentum transfer pumping is only possible below pressures of about 0. Matter flows differently at different pressures based on high vacuum pump laws of fluid dynamics. At atmospheric pressure and mild vacuums, molecules interact with each other and push on their neighboring molecules in what is known as viscous flow.
When the distance between the molecules increases, the molecules interact with the walls of the chamber more often than with the other molecules, and molecular pumping becomes more effective than positive displacement pumping.
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This regime is generally called high vacuum. Molecular pumps sweep out a larger area than mechanical pumps, and do so more frequently, making them capable of much higher pumping speeds. They do this at the expense of the seal between the vacuum and their exhaust.
Since there is no seal, a small pressure high vacuum pump the exhaust can easily cause backstreaming through the pump; this is called stall.
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In high vacuum, however, pressure gradients have little effect on fluid flows, and molecular pumps can attain their full potential. The two main types high vacuum pump molecular pumps are the diffusion pump and the turbomolecular pump.
Both types of pumps blow out gas molecules that diffuse into the pump by imparting momentum to the gas molecules. Diffusion pumps blow high vacuum pump gas molecules with jets of oil or mercury, while turbomolecular pumps use high speed fans to push the gas.
Both of these pumps will stall and fail to pump if exhausted directly to atmospheric pressure, so they must be exhausted to a lower grade vacuum created by a mechanical pump.
High Vacuum Pump
As with positive displacement pumps, the base pressure will be reached when high vacuum pump, outgassingand backstreaming equal the pump speed, but now minimizing leakage and outgassing to a level comparable to backstreaming becomes much more difficult.
Regenerative pump[ edit ] Regenerative pumps utilize vortex behavior of the fluid air.
The construction is based on hybrid concept of centrifugal pump and turbopump. Usually it consists of several sets of perpendicular teeth on the rotor circulating air molecules inside stationary hollow grooves like multistage centrifugal pump.
Due to high pumping rate from atmosphere to high vacuum and less contamination since bearing can be installed at exhaust side, high vacuum pump type of pumps are used in load lock in semiconductor manufacturing processes. This can be reduced by nearly 10 times by backing with a small pump.
A cryomodule uses cryopumping.
Other types are the sorption pumpnon-evaporative getter pump, and titanium sublimation pump a type of evaporative getter that can be used repeatedly. Venturi vacuum pump aspirator 10 to 30 kPa Steam ejector vacuum depends on the number of stages, but can be very low Performance measures[ edit ] Pumping speed refers to the volume flow rate of a pump at its inlet, often measured in volume per unit of time.
Momentum transfer and entrapment pumps are more effective on some gases than others, so the pumping rate can be different for each of the gases being pumped, and the average high vacuum pump flow rate of the pump will vary depending on the chemical composition of the gases remaining in the chamber.