Flat-sheet non-porous asymmetric poly(vinyltrimethylsilane) (PVTMS) membranes and composite membranes comprising a dense layer of polydimethylsiloxane/polyphenylsilsesquioxane (PDMS/PPSQ) block copolymer were evaluated for low-temperature bubble-free deoxygenation of water flowing in a two-channel countercurrent liquid-membrane contactor. A novel large-scale three-channel flowing-liquid-membrane module (selective membrane valve), designed for gas separation, is also described. The system comprised PVTMS or PDMS/PPSQ non-porous membranes which acted as gas-permeable barriers. A membrane system (SMV) in which pure water formed a flowing liquid membrane was evaluated to control hydrogen transfer rates. The liquid flowing along the turbulence-promoter spacers between the membranes reduced liquid-film resistance. The overall mass-transfer coefficients were found to be a function of the liquid flow rate. The liquid-film resistance controlled the rate of gas transfer in such membrane contactors.