Lip seal for piston-type flushometer

A flush valve including a body having an inlet and an outlet, a valve seat at said outlet, a piston assembly movable in said body toward and away from said valve seat to control flow from said inlet through said outlet, a pressure chamber in said body above said piston assembly and normally maintaining said piston assembly closed upon said valve seat,

• a relief valve in said piston assembly for venting said chamber to said outlet, means for opening said relief valve to vent said chamber causing said piston assembly to move away from said valve seat to open flow through said outlet,
• said body having an interior wall, said piston assembly having an outwardly-directed lip seal bearing against said interior wall, said lip seal being held between facing elements of said piston assembly,
• said lip seal including an insert and an elastomer overlying and substantially enclosing said insert, said lip seal having an elastomeric lip portion extending into contact with said interior wall and an elastomeric body portion extending between said facing elements, said insert having support elements in contact with at least one of said facing elements,
• the elastomer overlying said insert being spaced for the support elements so as to leave the support elements exposed for direct contact with said facing elements, the elastomer overlying said insert being spaced from the support elements so as to leave the support elements exposed for direct contact with said facing elements.