I've recently conducted an experiment investigating losses through pipes and fittings with water as the fluid and I'm a little unsure how to proceed calculating the theoretical pressure drop through the globe and gate valves for my lab report.
I know that for bends you need to essentially sum the frictional losses along the pipe and the head loss from the bend using Darcy-Weisbach and H_l = k*u^2/2g.
When calculating pressure loss across a valve is it the same procedure or do you not need to take into account frictional losses from the pipe? I think I'm getting a little confused by this as well from my experimental data as my results show the differential pressure across the valves increasing as the flowrate decreases - surely this is wrong? I thought that the differential pressure is proportional to flowrate and so shouldn't it be decreasing as flowrate decreases?
Any help would be much appreciated.
Edited by kkg14, 13 December 2016 - 02:05 PM.