Abstract: A pneumatic door closer has an elongated cylinder with a bore extending axially thereof and end walls, and a piston is slidably reciprocable within the bore. The piston is integrally fabricated of a synthetic resin with a generally circular cross section, and it has a circumferential groove adjacent one end thereof providing a neck portion dividing the axial length thereof into a head portion and a body portion. The groove has a generally radially extending wall surface on the head portion, an outwardly diverging wall surface on the body portion, and an axially extending bottom wall surface. The head portion has at least one passage extending through the head portion into the groove to allow air to flow therethrough. A sealing ring of resiliently deformable material is disposed in the groove and is of greater diameter than the piston so as to project outwardly thereof.