These couplings have a valve in the socket half (female) only which prevents fluid loss on the supply end of a line. The plugs (males) are normally unvalved. One way shut off couplings are often used in pneumatic applications and for breathing air lines.
Brands include Hansen, Coupleurs Gromelle (previously Tuthill, now the Eaton Coupling Group), Rectus, CEJN, Snaptite, Tema and Legris.
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