Swing-type check off er the least pressure drop and offer simple automatic closure; when fluid flow stops gravity and flow reversal closes valve.
旋启式止回阀压降最小，能够完全自动关闭，即在介质流动停止、重力和介质倒流的状态下自动关闭阀门。
2
Reversal point method which is adopted by gyroscope to seek north at present reduces the speed of north-seeking and is hard to make the instrument automatic.