Tap

A tap comprising a cylindrical barrel and a deformable cylindrical plunger which is movable along the barrel internally thereof, the barrel having an internal seat structure, a port in the wall thereof which port serves as an outlet from the barrel, and an inlet thereto, said inlet and said port being on opposite sides of said seat structure, and the plunger being displaceable along the barrel between first and second positions, said plunger being in said first position when sealing faces thereof are in engagement with said seat structure thereby limiting further movement of the plunger along the barrel and closing-off said port from said inlet, said sealing faces being spaced from said seat structure when the plunger is in its second position thereby to permit flow from said inlet to said port, said plunger having an edge which, as the plunger is displaced between said positions, moves across said port from a position on one side of said port to a position on the other side of said port, said seat structure comprising a first cylindrical surface which is part of the inner face of the barrel and a second circumferentially extending surface which is closer to the common longitudinal axis of the barrel and plunger than is said first surface and which is skew with respect to said first surface, said plunger including a first circumferentially extending face which co-operates with said first cylindrical surface and a second circumferentially extending face which is skew with respect to the first face and which co-operates with said second surface, engagement between said skew face and said skew surface upon closing of the tap deforming the plunger and increasing its outside diameter so that said first face is urged into engagement with said first surface.