Sign of the net emission of air is vent out all the water.
空气排净的标志是，排气孔中出来的全部都是水。
Water must not drip continuously from vent.
从排气口处必须没有水持续滴漏。
If water drips continuously from vent, second check is leaking.
如果水从排气口持续滴漏，则第二止回阀泄漏。
Fan, pump, air duct, water pipe, vent.
风机，水泵，风道，水管，风口。
Fan, pump, air duct, water pipe, vent.
风机，水泵，风道，水管，风口。
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