[en] A stand is developed to study the pumping characteristics of cryopumps for internal ³ He pumping in low-temperature cryostats. Isotherms of ⁴ He adsorption at 4.2 K were measured for three carbon adsorbents (commercial carbon SKT-4B, activated fibrous carbon AFC << Dnepr>>, metallized carbon BKTM). For three identical adsorption pumps with different adsorbents the speed of ⁴ He pumping is measured as a function of pressure and degree of the pump filling. The operation of these three pumps is investigated under conditions close to those of their use in low-temperature cryostats