Large Scale Central

A venture in venturi

I wanted to stop hijacking Cliffs excellent build thread.

Dan, correct me if I am wrong.

But the venturi is an amazing thing. As close to a perpetual motion machine that I know of.

But if I understand them correctly, when it comes to a steam locomotive injector, the inlet steam pipe and its pressure ( let’s call it X) is narrowed down in the venturi mechanism. This increases the steams velocity and inversely lowers its pressure. There is another “pipe” with a very small orifice perpendicular to the narrowed restriction that is the tender feed water line. As the increased velocity steam passes by that pipe it creates a negative pressure ( vacuum, X-) on the tender feed water pipe. This in turn sucks the water out of the tender. As the steam and now added water exit the venturi mechanism there is now more volume which now increases the pressure (X+) over and above the original boiler pressure (X) which is why the water from the tender can now be injected into the boiler.

If I am anywhere near right, then it is an amazing device in that it has no moving parts, yet it can overcome a given pressure and pump water into a high pressure vessel.

As I understand it, the only reason it is not a true perpetual motion device is there is energy loss due to friction with the steam/water and the walls of the venturi mechanism. No matter what it’s a damn efficient and effective way to introduce two substances at different pressures.

To clarify my question/understanding, how are we exceeding the boiler steam inlet pressure on the outlet side so that we can now inject the water being sucked from the tender into the boiler? It’s mind boggling to me that without some sort of compressor or turbine, any moving part for that matter, that we can exceed the pressure of a static vessel by using the static vessels pressure. Where and how do we gain pressure?

To me there are two variables that change, velocity and volume. The velocity changes when we constrict it at a given pressure but as soon as we return it to the original diameter pipe it should return to the original velocity.

But the difference is now we have increased the volume at the same given velocity by adding the tender feed water. At the outlet, is it this increased volume at the now original velocity that is inturn giving us the increased pressure?