The diametre of seat turns bigger when flap moves higher and smaller when flap lower.

根据阀瓣的这种形动形式，阀座通口的变化就是与阀瓣行程成正比例关系。

Rod material specification regarding to the diametre of round rod. Square rod and multi-shaped rod regarding to inside diametre.

棒材规格指圆棒直径、如方棒及多角形棒指内切圆直径。