The fixture could be gate valve, tee joint etc. For example a network consisting of 8 m pipe with an inside diameter 25 mm, 3 elbows (900 standard radiuses) and a gate valve 1/4 closed, and then equation 17 is

  

We substitute values of Le/D



 and this value is to be substituted in equation 10 to calculate frictional losses

References:
D. R. Poirier and G.H.Geiger: Transport: Transport Phenomena is materials processing 1994.
R. Schuhmann: metallurgical Engineering, vol .1 Engineering principles