Ask yourself, what kind of resource are we supposed to be?
The driving force behind our ability to answer questions is the wealth of experience represented in our user base. When someone has a question that isn't easy to answer by normal means—hard to search for, doesn't show up in Wikipedia, isn't accessible in physical texts, calls for extensive primary source research—and our particular collection of experience aligns with the topic of the question, that's where we shine.
It doesn't have to be a perfect fit; I'm not sure there is a perfect fit for this site, given the multidisciplinary nature of engineering. It just has to be a reasonable fit.
Your question is great because it gives three examples across the spectrum of quality:
- What is the purpose of these diversions in a natural gas line? is high quality—interesting, relevant, searchable, descriptive with an image, asks why and how. Many people should find (and have found) this question worth upvoting.
- Name of spring actuated component is moderate quality—relevant, descriptive with an image, as searchable as you could reasonably expect when the name is unknown. It's not quite as well formatted as the above and while the answer may be useful, it's not that interesting. And accordingly, it has fewer views and fewer upvotes than the first question, but it's still generally well-received, with +4/-1 score at the time of this revision.
- https://engineering.stackexchange.com/q/1846/368 is low quality—a little interesting, invites why and how answers by asking about usage, includes images. On the other hand, it includes few details; it's hard to tell if it's relevant without knowing the answer; it's probably not going to be searchable based on "maritime related tool" as the description. Worst of all, the user claims to have come across it in a museum, but doesn't know what it is? There was no information attached to the exhibit? There was no curator to ask? The author seems to have missed their best (and perhaps, only) opportunity to get an answer. Verdict? Say hello to my little friend:
So I agree with 99% of Trevor's answer; how we react to any type of question is dictated by its quality. Where our opinions diverge is that I don't think there's a compelling reason to close questions in this category simply because they're low-quality. They're not unclear, they're not broad, they're not opinion-based; they can be answered, and those answers may be useful.
Until and unless we have evidence that the mystery item is definitely not related to engineering—e.g., it is a teapot, and not even a special "engineer's teapot" where we could say it's about engineering history/culture—I would simply downvote and move on.
I can imagine circumstances when I would be much freer with a close-vote, and shift the burden of proof onto the author of the question to show that whatever it is, it's related to engineering. But most of them are silly straw-men. I don't expect anyone to post a food item, for example, and ask us what it is. (Engineer's Metric Sandwich? Some people juggle geese...)