| 摘要 |
An elastomeric seal (1), particularly for mining roof supports, has a circumferentially extending primary sealing ridge (4) for sealing against the cylinder wall (15) at both low and high pressure differentials. In order to provide lubrication of the primary sealing ridge, a series of fluid reservoirs (10) are defined adjacent to opposite sides of the primary sealing ridge by a respective web (5) of secondary sealing ridges, each web consisting of a circumferential ridge (6) and a series of axial ridges (7). The secondary ridges (6, 7) are dimensioned such that at low fluid pressure differentials across the piston there is a radial clearance between the secondary ridges and the cylinder wall, to reduce seal friction at low pressures, but at high pressure differentials the portion of the seal adjacent to the low pressure chamber is elastomerically deformed to bring the web of secondary ridges at that end into sealing engagement with the cylinder walls, to provide a secondary seal and to trap fluid in the reservoirs. The seal may be arranged to be single acting or double-acting.
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