| 摘要 |
<p>An improved tennis ball having an integrally molded valve in the sidewalls thereof for assuring constant pressure within the ball and, therefore, constant playing characteristics. The valve is characterized by being of unitary construction and having a normally open and a normally closed portion. The valve is constructed of a tapered deformable elastomeric material such that the normally closed portion seals the ball against low initial internal pressures sufficiently to allow the internal pressure within the ball to deform the normally opened portion into wedged engagement with the passageway through the wall of the ball containing the valve. As thus configured, increased internal pressure wedges the normally opened portion increasingly tightly into the passageway to provide a tight seal which is resistant to opening upon impact of the ball. The normally opened portion is provided with knife edges and a polished surface on the interior to provide leak-free sealing. The fabric covering of the tennis ball is made of a gas-permeable material disposed over the valve opening which is further protected by a gauze filter between the opening and the covering fabric. The ball can be pressurized to predictable bounce characteristics regardless of altitude and temperature by placing the ball within a sealed container at the play site and then reducing the volume of the container a fixed amount.</p> |
