Does anyone know what this is?

Mar 2019
Victoria, Australia
Posting here since, well. I have no clue where this should go. Excuse me if is in wrong section

So, I was working in the museum the other day, just like normal when this guy donates us this interesting little piece of equipment. Except that none of us know what it is, how it is used, when it was made, or really... anything about it. As you can see, someone has gone through the effort of scratching out all the labels and stickied writing on the box. What little writing is available does not make any sense as it's completely out of context.

I am guessing it is some kind of pressure measurement device -- perhaps for a diesel pump. But I am looking for any detail or information, year, maker or anything any of you might have. Also, there is a little valve that came with it, along with an assortement of springs. The valve has a bleed point on it and the springs have a central rod in the centre. A larger spring is also there - perhaps for the main cylinder? Outside of that there is an alan key and two other bobs which I'm not sure what they're for.

Outside of that, the quality is really good and there is visible machining marks on the utensils. The valve accompanying looks newer in make - perhaps replacement or later addition. The box itself is old, from at least the 1950s and the springs inside have rusted. The main took itself is in good condition (having been wrapped in an oil-cloth) and is free of any major issues and seems to function well enough. You can see a small little string coming out from the main cylinder. That string has heavily deteriorated but looks about1940s era. But I don't know if it's original - it too could have been recycled from another place or part.

So. Here I am, appealing to the a greater, more knowledgable audience whom will hopefully know what this is: