An impulse air turbine arrangement for use with a reversing bi-directional air flow in a wave power plant comprises an axial flow turbine rotor with volutes mounted one each side of the turbine rotor to direct the reversing air flow to and from the turbine rotor. Each volute extends circumferentially with respect to the turbine axis between a radially outer opening and a radially inner opening. The radially outer opening is oriented for input/output of the air in a tangential direction and the radially inner opening is oriented axially to impinge/receive swirling air flow onto/from the turbine rotor.