Abstract: An improved ringless piston construction having particular use in a closed fluid system. The piston includes a metal core, which is attached to a piston rod, and a resilient outer member is secured to the core and is formed from a material, such as nitrile rubber. The outer member includes an outer peripheral surface and at least one of the axial ends of the outer surface is provided with a tapered lip. The resilient outer member also includes an inner flange that is spaced radially inward of the base of the lip, and the lip and flange, in combination, define an annular recess having outwardly diverging walls. When subjected to fluid pressure, the lip will be deformed outwardly into sealing engagement with the inner wall of the cylinder, while the flange acts to deflect the fluid toward the lip to increase the sealing pressure.