It is like a water flow - if you block one direction, it flows to other directions, or overflows. There's got to be an outlet.

就像水流，你堵住了一个方向，他就流向另一个方向，要么就大水冲了龙王庙，反正必须得有一个口子。

youdao

Pressing water down creates a lot of pressure on the palm because you are changing the direction of the water flow (from towards you to downwards).

往下压水时在手掌处产生了很大的压力，因为你在不停地变化水流的方向（从对着你到朝下）。

youdao

A check valve is a mechanical valve that only permits water flow in one direction.

检查阀(单向阀)是一个手动阀门，这样水只能往一个方向走。

youdao