Hello, my first post here. I encounter a situation frequently at work that I'd like help with so here it is... When I isolate a particular section of pipe (by closing valves), I then bleed off the pressure in the isolated section (volume of isolated pipe varies from 3 cubic meters up to about 18 cubic meters). I often bleed the pressure down to about 10psi. Then I observe a digital pressure gauge to confirm that the closed valves are holding. There is often upwards of 300-800 psi of crude oil in this pipe. Occasionally, the pressure in the isolated section climbs slowly 20 psi/minute (give or take). Sometimes the valves hold completely and no pressure rise occurs in the isolated section and then we're all happy. But when the pressure does climb, how can I get a "liters/minute" flow rate so that I know how much product will be leaking past the valves after I have drained the isolated section and I open that isolated section for maintenance. I need to know if the leakage is manageable or not. I assume the variable numbers you need to know are: isolated pipe volume: 5 cubic meters time: 60 seconds pressure rise: 10 psi mainline pressure: 500 psi incoming flow rate (leakage past closed valve): ?? Liters/minute Is there a formula for this that will work on various sizes of isolated pipe sections? Maybe mainline pressure is irrelavent? Do you need more info? Thanks!