A hemostatic valve device for use in inserting an interventional device into a body lumen of a patient. The valve device includes a housing that defines a cavity between first and second end openings. A valve structure is disposed within the cavity, and defines a variable diameter channel for receiving the interventional device. An annular chamber is generally formed between the valve structure and the housing inner surface, and can be filled with fluid. The housing is movable between first and second positions so that the volume of the cavity and the diameter of the channel vary to a degree for the valve structure to form a seal along the interventional device inserted within the channel. The valve structure may be configured to seal without substantial twisting.