Check the valve parts before installation. Open and close the valve by hand for a period check the open-close position of the valve gate.
检查阀门各部位是否有松动现象，对阀门进行手动开启、关闭一个周期是否有异常现象，同时检查阀门的启闭位置是否准确。
A pressure drop through the bit maintains the tool in the open position while the return springs close the pistons when flow decreases.
随后钻头处的压力降使扩眼工具处于打开状态，当流速下降时弹簧将活塞收回至原处。
A pressure drop through the bit maintains the tool in the open position while the return springs close the pistons when flow decreases.
随后钻头处的压力降使扩眼工具处于打开状态，当流速下降时弹簧将活塞收回至原处。
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