A fluid-tight connection between a pair of pipes (1, 2) containing hydraulic fluid is formed by a pair of connectors of the invention. Each connector has a body part (4, 5) engaged respectively with the pipes (1, 2), the body parts being coupled together by a coupling sleeve (3) which engages a shoulder 20 of one of the body parts and is locked to the body parts by a circlip 23 engaged within grooves 22 and 25 respectively in the other body part and the sleeve. Each body part has a respective seal member (6, 7) each incorporating a diaphragm (6B, 7B) sealing over an end of its associated body part and a bead (6A, 7A) engaging the internal wall of the sleeve (3). Air trapped between the diaphragms (6B, 7B) is expelled past the seal members during insertion of the connector parts into the sleeve. Application of system pressure subsequently ruptures the diaphragms to establish communication between the pipes (1,2) and urges the seals outwardly to seal against leakage of system fluid.