I have a pipe dn 20 in which the pressure is 6 bar. When I open the valve at the end of the pipe how much water will flow from it? How to calculate? are the anny practical figures for this?
For flow of any fluid there must be some differential pressure required. In your case when you open the valve, there will be some pressure drop in the pipe and your outlet is at atmospheric pressure. so find out the differential pressure. Check the website