How did this tap worked?

[nokia2010]

1st of all, hope I will post it on the right area.

In old (around 1930) German book, "Handbuch for hochbaus" (I think it translates as "General manual for construction") by Professor Paul Schimdt I found some intresting taps, but with no explination on how the on/off part worked. I've transalated the page, but no info about how they worked.
I guess that the spring pushed the pin down, but as you moved the handle, the pressure of the spring was reduced, letting watter to fhlow trough. You had only a certian procent mixing, not like at modern taps, where you can control both the flow and the mix.

Probably they are the same as "robinete medicale" ("medichal taps") described at pg. 166 in the book "Materiale pentru instalaţii sanitare şi de gaze" ("Materials for sanitary and gas installations") by A. Simonetti and Engineer I. R. Niţescu, published in 1959 by Editura Tehnică (The Tehcnical Publishing House).
Never seen for real a tap like this.

 

[ShaunCorbs]

It might even have seats in the bottom of the brass block that moves when you turn the handle

 

[Ric2013]

It looks to me that there may be separate temperature and flow controls. The 1439 tap shows some kind of screwdown valve (globe valve?) under the rightmost tap head, so presumably both tap heads on the 1438 and 1439 are adjustable, the difference between the two taps being that one has a course-thread lever and the other a more conventional knob you would turn (or, possibly, push-to-open control, though I'm not convinced that is a spring) in the middle of the two screwdown valves.

Possibly the central valve only adjusts the flow and is not a complete shutoff, so you adjusted the mix using the side valves as you would with any manual deck mixer, but could quickly tweak the flow using the control valve? I've used a shower based on that same principle, so I can see it would work; though there could be crossflow issues, so it wouldn't meet current standards.

I'm thinking there's a kind of helical gate (that rotates, as Shaun suggests) to control the flow, but the drawing isn't entirely clear on what it is trying to show us.

 

[nokia2010]

The water flow was adjusted separatley by removing the 2 caps and using a screwdriver.
On the Romanian version you could also adjust the flow like at a normal tap. But not even in a Romanian book I couldn't find a tehcnical description of such taps, only they are mentioned.
Probably there is a book or catalogue, but finding one is extremly hard around here. Water in the house was and still is less common then electricity.