I'll get straight to the point. It took me a long time to figure out what valves were good for, or even what they did in ONI. Obviously, they allow gas and liquid flow only one way, do not require power, etc. But recently, I discovered a way they can be used to more efficiently spread the flow of such resources through your colony.

The process is actually really simple. All you need to do is hook, say, a liquid valve up to your main water pipe that goes to your Lavatories and Sinks. However, do not have the flow output of the valve running to your toilets; instead, hook the input to the pipe itself, and leave the output somewhere off to the side. This may seem counter-intuitive, but what this does is it causes part of the water flow to be siphoned off from the pipe, and sent to the output.

I used this to solve the issue of how I was unhappy with my main water pipe just stopping after it flowed to the toilets, and me not wanting to snake it all the way back around to my Carbon Skimmer in my coal-fired power plant area. Instead, I installed a valve on the pipe near my water cistern, and bam! Water just flowed through the output at an easily settable rate, plenty and to spare to run the skimmer all cycle long. And all this without interrupting the flow of water to my bathrooms at all; all I did was 'borrow' some water from the pipe, since the bathrooms didn't need so much anyhow. This prevented me from having to build a whole new length of liquid piping, or even a new liquid pump entirely, as I could now much more efficiently use the water I had already available.

There! Now you are armed with the knowledge of precisely what valves do. I wrote this short guide because I was unsatisfied with what the tool-tips told me; if I'd known before they could essentially siphon off pipe flows, I would have used them a LOT sooner, as adding in valves makes my colony feel a lot more clean and efficient with its resources.