Meaning of “underpressure”

Question

I saw “under pressure” in a description of a machine that uses a pressure lower than the ambient pressure to do its work, and I am pretty sure that is a mistranslation of the German »Unterdruck«, which literally translates to “underpressure” (note this is one word, whereas the translation used is two words). I was surprised to find “underpressure” as a possible translation of »Unterdruck« using LEO, which was confirmed by Wiktionary, but Merriam-Webster only forwards to me to “under pressure”.

Wiktionary describes its meaning as

insufficient pressure; a marked drop in pressure

and lists “overpressure” as an antonym.

This leads to my question of: What does “underpressure” mean exactly?

I have a feeling that it describes more of a non-intentional, out-of-spec low pressure (similar to how I understand “overpressure” as opposed to “high pressure”), whereas an intentional low pressure like you would expect in that machine would be called one of the following:

(partial) vacuum

low pressure

negative pressure

Answer 1

I saw “under pressure” in a description of a machine that uses a pressure lower than the ambient pressure to do its work

I think you're correct and it is a mistranslation. The appropriate term for an enclosed area with pressure lower than the ambient pressure in English would be "negative pressure".

Describing something as "under pressure", would mean that the system is pressurized. For example "under pressure drill kits" are designed to work on pipes that have something flowing through them (the pipe is under pressure).

"Low pressure" machines work at a positive pressure, but at pressures much less than other similar machines. For example "low pressure molding" instead of "high pressure injection".

I have seen "underpressure" as one word used for names of businesses, like pressure washers or therapeutic masseuses, but I would read it as a typo or mistranslation if I saw it as a description of a negative pressure machine and I would expect to see "low/high pressure" as a warning if a pressure was outside of an acceptable range.