Below is a list of Piston Seals manufacturers from Union City, California. Piston seals, also called piston packings, are seals that mount on a piston head. Piston heads move through the bore of hydraulic, pneumatic and engine cylinders. They fit onto the shaft with the sealing lip contacting the housing bore. The outside diameter lip seals against the bore, while the inside diameter seals to the gland, stretching to ensure a tight, waterproof seal and improving the piston’s stability.