Pneumatic door closer

A pneumatic door closer for use between a door and its frame to provide controlled closing motion of the door, said door closer comprising:

• (a) an elongated cylinder having a bore extending axially thereof, a first end wall having a coaxial opening therein, and a second end wall;
• (b) a piston slidably reciprocable within said bore between a first position adjacent said first end wall and a second position adjacent said second end wall, said piston and said cylinder defining a chamber between said piston and said second end wall, said piston being integrally fabricated of a synthetic resin and having a generally circular cross section and axially spaced first and second end surfaces, said piston having a circumferential groove dividing the axial length thereof into a head portion adjacent said second end wall and a body portion with said groove providing a neck portion therebetween, said head portion and said body portion having the same diameter, said groove being defined by a generally radially extending wall surface on said head portion, an outwardly diverging wall surface on said body portion, and an axially extending bottom wall surface, said head portion having at least one passage with a closed periphery spaced inwardly from a periphery of the head portion extending through said head portion into said groove adjacent its base to allow air to flow therethrough between said chamber and groove;
• (c) a sealing ring of resiliently deformable material disposed in said groove and of greater diameter than said piston so as to have a peripheral portion projecting outwardly thereof, an axial dimension of said groove increasing radially outwardly in axial dimension to a dimension greater than the diameter of said ring so that said ring may move axially therewithin, said at least one passage being substantially unobstructed by said sealing ring, whereby, when said piston moves toward said second position, said sealing ring bears against said diverging wall surface of said groove and the wall of said cylinder thereby to restrict flow of air from said groove and thereby from said chamber, and, when said piston moves towards said first position, said sealing ring bears against said generally radially extending wall surface of said groove on said head portion to permit flow of air thereby into said groove and into said chamber;
• (d) an elongated piston rod having one end secured to said piston and its other end extending outwardly of said opening in said first end wall, said piston having an axial bore extending therethrough and said one end of said piston rod extends through said axial bore of said piston and is secured therein, said piston rod having a portion protruding from said head portion of said piston and of a larger diameter than a diameter of said axial bore of said piston and bearinq against said first axial end surface, said piston rod having at least one staked boss thereon disposed against the second axial end surface of said piston, said protruding portion and said at least one staked boss firmly engaging and imbeded in said body portion of said piston to prevent rotational movement of said piston relative to said piston rod said protruding portion of said one end of said piston rod and an end of said axial bore of said piston adjacent said second end wall of said cylinder being dimensioned and configured to form a substantially airtight seal;
• (e) an axially elongated coil spring disposed about said piston rod and bearing against said piston and said first end wall to urge said piston towards said second position;
• (f) air flow control means on said cylinder allowing air to flow outwardly of said chamber in a controlled manner as said piston is moved within said cylinder toward said second position and;
• (g) means for attaching said cylinder and said piston rod to the door and its frame.