An applicator, for example an injector (100), includes a flow control means including a first member (2) and a second member (6) for controlling flow from an inlet (4) to an outlet (5). A hinged linkage (17) is provided having a first end (18) rotatably engaged with the first member and a second end (19) rotatably engaged with the second member. The linkage (17) is moveable between a collapsed position and an over-center locked position which prevents relative movement of the first member (2) towards the second member (6). Linkage unlocking means (28) are provided which move the hinge (22) away from the over-center locked position so that the first and second members can be moved together.A similar linkage (10) prevents unwanted movement of a needle shroud (8).A needle shroud (8) which can be used to remove the needle (7) from the injector (100) is also described.