# Water pressure out of pipe insertions in a bigger pipe in which water is flowing

I've got a very basic knowledge of fluids and can't comprehend this situation. I've tried to look it up on my own but I guess I couldn't find the right keyword to search.

I've got a pipe P in which water is flowing water. In this pipe P, I've got pipe insertions A and B. These insertions, although same in width, are different in length, with pipe B inserted deeper into the pipe P.

Now my question is, what will be the pressure out of pipes A and B, if water is at level L1, at Level L2 and if the pipe P is completely filled with water?

Also will the pressure change if the width of pipes A and B are changed?

The pipe P is approximately 8 inches in diameter. I'm not looking for any exact numbers, just the relation. If there is a certain topic of fluids that I'm missing, then kindly direct me in that direction.

I suppose at some point, Bernoulli's theorem might be applied, but I can't figure how. I've also looked up capillary action and venturi meter pipes, but still I couldn't apply them to my situation.

Any help is highly appreciated. Thanks in advance.

• Is the pipe P pressurized, like a water supply pipe? Or vented, like a sewer or drain pipe? – Bob Jacobsen Apr 9 '18 at 5:11
• Yes, it is a water supply pipe. Also, pipe A and pipe B bring water further to two separate apartments of our building. – Shivam Sharma Apr 9 '18 at 8:53

## 1 Answer

First, pressurized water supply lines almost never have air in them. When they do, you get water hammer effects and water spurting out of faucets at high speed instead of flowing evenly.

That said, both pipes will have the same pressure when no water is flowing. A static pressure gauge will show the same.

Turbulence in water flow causes pressure loss. If significant water is flowing, it looks like water going into B will be more turbulent, hence more loss, hence a lower pressure than A. This is why some plumbing fittings are “faired” to smooth flow.

• Thanks for your time. There is however one caveat, this pipe B, comes into my apartment and when I open the tap, there's a lot of air pumping out along with water. Also, this supply pipe has water inside it for only 2 hours in the evening, everyday. So, in this case, the pressure inside B still be the same as in A? – Shivam Sharma Apr 10 '18 at 18:50