| 主权项 |
1. A plunger for use by being fitted into a circular-shaped cylinder of a pneumatic dispenser that employs pressurized air to discharge a viscous material,
wherein the plunger is configured to divide an inner chamber of the cylinder into a first sub-chamber that stores the viscous material and a second sub-chamber into which the pressurized air is charged, the first and second sub-chambers being coaxially aligned with each other, the plunger has a first portion configured to face the first sub-chamber and a second portion configured to face the second sub-chamber, the first and second portions being coaxially aligned with each other, the second portion is a hollow structure having a circumferential wall that is configured to be coaxially aligned with an inner circumferential surface of the cylinder, the circumferential wall being an elastic structure that is elastically deformable in a radial direction of the plunger, the first portion is an at least substantially solid structure serving and is more rigid than the second portion, an outer circumferential surface of the first portion has a first annular groove and a first land, which extend circumferentially around an axial direction of the plunger, the first land is configured to locally oppose the inner circumferential surface of the cylinder, the first land has an outer diameter that is sized so as to provide a first radial clearance with the inner circumferential surface of the cylinder, the first radial clearance has a width that enables venting of air, which is within the first sub-chamber, from the first sub-chamber to the second sub-chamber when viscous material is filled into the first sub-chamber, and blocks viscous material from flowing from the first sub-chamber to the second sub-chamber due to the viscosity of the viscous material, and the first land is not displaceable in the radial direction with respect to the axial direction of the plunger, an outer circumferential surface of the second portion has a second annular groove and a second land, which extend circumferentially around the axial direction of the plunger, the second land has an outer diameter that is sized so to be at least substantially in local contact with the inner circumferential surface of the cylinder such that said air venting and said viscous-material blockage are achieved, and such that pressurized air, which is within the second sub-chamber, is at least substantially prevented from flowing from the second sub-chamber to the first sub-chamber by leaking between the second land and the cylinder, and the second land is displaceable in the radial direction with respect to the axial direction of the plunger, and in a free state in which external forces are not being applied to the plunger, the outer diameter of the first land is smaller than the outer diameter of the second land. |
