The main advantages are the absence of oil or other contaminants, low cost and vibration free operation because there are no moving parts.
The main disadvantages are that it cannot operate continuously and cannot effectively pump hydrogen, helium and neon, all gases with lower condensation temperature than liquid nitrogen.
A sorption pump is usually constructed in stainless steel, aluminium or borosilicate glass.
The typical molecular sieve used is a synthetic zeolite with a pore diameter around 0.4 nanometer ( Type 4A ) and a surface area of about 500 m2/g.
This is achieved by cooling the pump body to low temperatures, typically by immersing it in a Dewar flask filled with liquid nitrogen.
In the desorption phase the pump is allowed warm up to room temperature and the gases escape through the pressure relief valve or other opening to the atmosphere.
In the regeneration phase the pump body is heated to 300 °C to drive off water vapor that does not desorb at room temperature and accumulates in the molecular sieve.
A sorption pump does pump all gases effectively with the exception of hydrogen, helium and neon which do not condensate at liquid nitrogen temperatures and are not efficiently adsorbed by the molecular sieves because of their small molecular size.
This problem can be solved by purging the vacuum system with dry pure nitrogen before pump down.
The valve is closed before hydrogen, helium or neon can back-migrate into the vacuum vessel.