Hello, First time poster here! I am hoping someone here may be able to share some insight on my problem. I am a canadian engineer working for a local gas company. We want a means to calculate the time it takes to commision a line (flare at the downstream end). See the free body diagram attached: As soon as the squeezer is released, and gas starts flowing into the empty pipeline (length L1), the gauges we use (gauge P2) wont pick up a reading, yet the upstream gauge (gauge P1) remains the same. Over time, the pressures will equalize, and gauge P1 and gauge P2 will equalize, but typically we never flare the line for long enough to see that happen. My question is, how do we measure P2? Does it need to be with a pitot tube? We use static gauge pressures, does it makes sense that a static gauge pressure wont pick up a reading at P2, at least initially? THanks!