Control type: normally closed, normally open, double acting.

控制形式：标准常闭、常开、双作用。

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Usually divided into normally open, normally closed and self-holding three.

通常分为常开型，常闭型和自保持式三种。

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Usually divided into normally open, normally closed and self-holding three.

通常分为常开型，常闭型和自保持式三种。

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