This might be better in the "Engineering Language" forum. Each of those is intended to be the present participle of their principle word, "depressure" and "depressurize". However, Merriam Webster doesn't recognize the root word "depressure" (except as an obsolete form of the word "depression") so I would guess that this "word" and its derivatives are not words at all. They were likely made simply by joining "de" and "pressure" together to mean the same thing as depressurize.

As far as interpretation goes in the texts, I would interpret "depressure" to mean the same thing as depressurize.

Technical applications have a tendency to make up words as jargon. I worked at a plant that commonly used the term "pluggage" to refer to material that plugged up a line. Such a word doesn't exist in English, but was a commonly accepted "word".