a latching and sealing device suitable for use as a cover seal for a plunger or piston in a syringe or plunger pump includes a cylindrical seal member having a body portion and lip - and - latch means for both sealably engaging a surrounding surface and latching to the piston . a spring disposed in between the lip - and - latch means and the piston provide a constant sealing pressure while allowing the piston and seal member to be moved within a bore . sealing between the lip - and - latch means and the bore is enhanced by use of a berm and notches radially aligned with the biasing spring .