tabs 25a and 25b and is pushed by a spring 29 against a sealing surface 30 and gasket 30a within the coupling the coupling 23 includes an internal cylindrical surface 23a which has a pair of opposed short axial ridges 31a and 31b and a pair of equally spaced opposed longer axial ridges 32a and 32b the ridges define two distinct relationships between the couplings and the opposed shutter valves the tabs 25a and 25b may be accommodated in the spaces respectively between the ridges 31a 32a and 32b 31b or in the spaces respectively between the ridges 31a 32b and 32a 31b the same relationship occurs in the coupling 24 which has an internal cylindrical surface 33 which has a pair of opposite short axial ridges 34 and a pair of opposite long axial ridges 35 similarly the ridges define two distinct relationships between the coupling and the shutter valve tabs 28a 28b fig7 and 9 illustrate in solid lines the shutter valve 28 in the first relationship of mutual spacing of the couplings when the couplings approach one another shutter valve 28 moves and rotates together with the coupling 24 due to the force exerted by the ridges of the surface 33 on the tabs and moves to the position shown in broken and dotted lines with the tab 28a against the long ridge 32b of the cylindrical surface 23a of.