| 摘要 |
<p>A drilling equipment comprising a drill bit (19) and a pneumatically operated sinker drill machinery therefor comprises a non-return valve (20) which is positioned between said drill bit and said sinker drill machinery and is in the form of a dome-shaped valve member (25) formed of elastomer material and having throughflow slots (26) adapted to open when compressed air is supplied in one direction through said valve member, and to close again when the supply of compressed air is discontinued, to prevent flow in the opposite direction. The throughflow slots (26) preferable have been formed by cutting said dome-shaped valve member (25) without any appreciable removal of material. </p> |
