How do you determine whether or not a pipe is pressurized?
There are flow meters you can install outside your pipe (in the form of 2 half shells that are placed around the pipe), they are called, clamp-on.
Indeed, we considered a meter, but in this case there is no water circulation in the pipe. The pipe is full but plugged 330 feet further along, which we discovered after using a tracer.
I see no other solution than pressure tapping. But be careful because it could be a dead pipe in which case poor water quality, or more dangerous still a gas pipe!
From what I gather, clamp-on ultrasonic flow meters that measure transit time can confirm the presence of fluid in the pipe even if there’s no flow because the speed of sound is different in water an in air.
Measuring pipe pressure and possibly its stability over time could give you another metric. Primayer makes data loggers that can be connected to your water intake.
A tried and true solution: if the pipe is in cast iron, you can heat it with a torch and observe the diffusion of heat. If it is full of water, the diffusion will be quick; be careful if it's gas though, so don't overheat it!
Thank you for all your ideas -I would not have thought of the torch technique. Worth trying.
It seems to me that installing a pressure gauge downstream would do the trick.