Learn Spanish (Latin America): La válvula no funciona, es decir, no la abras. - The valve does not work, that is to say, do not open it.

es decir translates to "that is to say" or "in other words." In this sentence, it connects the problem (la válvula no funciona) to the logical instruction of what to do about it (no la abras). You could definitely use o sea here; they are very similar, though es decir sounds slightly more formal, while o sea is extremely common in everyday spoken Spanish.

Why is the verb abrir conjugated as abras?

This is the negative command form telling someone what not to do. For negative informal commands (giving an order to tú), Spanish uses the present subjunctive form. Because abrir is an -ir verb, it takes the opposite vowel ending -as, making it no abras. If it were just a normal statement like "you aren't opening it", it would be no abres.

Why does the pronoun la come before the verb in no la abras?

While object pronouns attach directly to the end of positive commands (like ábrela to say "open it"), the rule changes for negative commands. When you tell someone not to do something, the pronoun must go between the word no and the verb. The la here replaces the feminine noun la válvula.

Why use funciona instead of trabaja to say the valve doesn't work?