Miniature cryosorption vacuum pump for portable instruments

This article describes the design, construction, and laboratory testing of a low power, low‐weight, and compact cryosorption vacuum pump for backing, roughing, or other intermediate pressure applications. Novel features of this pump include a high‐temperature, low‐pressure desorption cycle allowing useful pumping capacities of many gases at 77 K, and the use of a miniature cryorefrigerator. The laboratory test pump used a cold finger cooled by a single stage helium Stirling cycle refrigerator having a 1 W capacity at 70 K, weighing between 1.6 and 2.0 kg, and consuming less than 45 W of electrical power. Calculations show that pumping rates for N₂ at 1×10⁻⁴ Torr could be up to 10 Torr ℓ s⁻¹ short‐term, and approximately 0.5 Torr ℓ s⁻¹ continuously. Our laboratory working model showed that it was possible to pump at pressures down to approximately 2×10⁻⁵ Torr using a type 5A molecular sieve. Pumping rates for air of up to 5 Torr ℓ min⁻¹ were achieved. Using desorption at 363 K and 2×10⁻¹ Torr, the capacity of type 5A molecular sieve was determined to be approximately 16 Torr ℓ g⁻¹ at 1×10⁻⁴ Torr. It is anticipated that such a pump would be useful in certain portable instruments such as portable gas chromatograph‐mass spectrometers used for occupational health applications, or other applications where weight, available power, and pumping requirements were compatible.