If the valve seat diameter is not known, the port diameter can be assumed to be the seat diameter for estimating purposes.

阀门阀座直径。如果不知道阀门阀座的直径，则可以将端口直径作为阀座直径进行估算。

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Note: the seats and springs of the first and second check modules are not interchangeable. The heavier spring and smaller diameter seat belong with the first check module.

注：第一和第二止回阀模块的阀座和弹簧是不可互换的。较重的弹簧和较小直径的阀座属于第一止回阀模块。

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