How do pipe fittings contribute to pressure loss?

Pipe fittings (elbows, tees, valves, reducers) cause additional pressure losses beyond straight pipe friction. These are typically expressed as equivalent length (Le) of straight pipe or as velocity heads (K-factor): dP = K*(rho*v^2/2). Typical K-values: 90-degree elbow 0.3-0.9, gate valve (open) 0.1-0.2, globe valve (open) 4-10, check valve 1-2. Fittings can represent significant loss in short piping runs - total fitting losses often exceed straight pipe losses in process plants.