A rotary valve for fluid flowing in a pipe. The valve has a body provided with upstream and downstream segments located on either side of a central recess constituting a seat into which a rotary sealing element, including a through-channel, is inserted. A decompression insert is arranged in the upstream segment and provided with a first cylindrical section having an outer cross-section equal to the cross-section of the upstream segment, a second cylindrical section having a cross-section that is narrower than the first cylindrical section, and a third section, referred to as frusta-conical connection section, for connecting the first and second sections. The decompression insert has a plurality of radial openings provided in at least one of the walls of the second and/or the third sections in order to diffuse the fluid toward the through-channel of the sealing element during a partial opening phase of the rotary valve.