The differential hardness of the hard metal bearing surface to the soft metal bearing surface is preferably at least about 1.5, and is preferably less than about 3.
所述硬金属轴承表面相对于所述软金属轴承表面的硬度比优选为至少大约1.5，并且优选为小于大约3。
Metal cock ring soft seat surface pressure to the bearing surfaces, such as the valve core and valve seat is concentric ring surface can be a double tight closure.
金属旋塞表面压向阀座环软支座表面，如阀芯和阀座环表面是同心的，就能得到双重严密的关闭。
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