Abstract: A tire pressure holding system for a vehicle includes a pump mounted in the center of a wheel for discharging compressed air in synchronization with revolution of the wheel, the pump including a discharge section from which the compressed air is discharged, a conduit connected to the interior of the tire and the discharge section of the pump, a check valve mounted in the conduit for preventing the air in the interior of the tire from flowing to the pump side, and a release valve mounted in the conduit for releasing the compressed air from the pump outside when an internal pressure is at or above a predetermined value in a section of the interior of the conduit between the check valve and the pump.

Abstract: A tube blank 2' whose inside is divided into an air chamber 3 and a sealant chamber 7 by a partition wall 5 has an air relief port 4.sub.1 provided in a sealant chamber peripheral wall 4o and communicating a sealant chamber 7. At a vulcanizing step, the tube blank 2' is placed into a heating die 18, and a gas of a high temperature and a high pressure is supplied into an air chamber 3. This causes air remaining in the sealant chamber 7 to be discharged through the air relief port 4.sub.1, while bringing the partition wall 5 into close contact with the sealant chamber peripheral wall 4o, thereby performing a reliable vulcanization. When the tube blank 2' is removed from the heating die 18, the sealant chamber 7 is not expanded because of the existing of the air relief port 4.sub.1 and therefore, the partition wall 5 cannot be provided with an expanding tendency that forces the wall 5 to be stretched toward the air chamber peripheral wall 4i.