Abstract: A subsea coupler has an internal chamber (6) adapted for the reception of fluid under pressure, a passageway (7) for the ingress of fluid to the chamber, a valve seat (9) in the passageway, a poppet comprising a body (4) which is engageable with the valve seat to close the passageway and a head (3) which fits against the body and is moveable away from the body. The body (4) includes a channel (11, 12) for communicating fluid pressure from the internal chamber to a region between the head and the body whereby the head can be moved away from the body to relieve pressure in the chamber while the body is in engagement with the valve seat.