Question 1

What is a minor loss coefficient (K)?

Accepted Answer

K is a dimensionless coefficient that converts a fitting, valve, bend, entrance or exit into an equivalent head loss using the velocity head: h = K·V²/(2g), where V is the mean pipe velocity. 'Minor' refers to localized losses, distinct from the distributed friction loss along the pipe wall.

Question 2

What is the K value for a 90-degree elbow?

Accepted Answer

A standard threaded 90° elbow is about K = 0.9; a flanged regular 90° elbow about 0.3; a long-radius 90° elbow about 0.6 threaded or 0.2 flanged. Values vary with size and manufacturer; use Crane TP-410 or vendor data for final design.

Question 3

What is the K value of a gate valve versus a globe valve?

Accepted Answer

Fully open, a gate valve is about K = 0.15–0.2, a ball valve about 0.05, a swing check valve about 2.0–2.5, and a globe valve about 10. The globe valve's tortuous path makes it roughly 50× the loss of a gate valve.

Question 4

What is the entrance and exit loss coefficient?

Accepted Answer

A sharp-edged (flush) pipe entrance is K = 0.5; a re-entrant/projecting entrance is about 0.8; a well-rounded entrance is 0.04–0.05. The exit loss from a pipe discharging into a large reservoir is always K = 1.0 (the full velocity head is lost).

Question 5

How do I combine minor losses with friction loss?

Accepted Answer

Sum all fitting K values and add the pipe friction term: h_total = (ΣK + f·L/D)·V²/(2g). For long pipelines minor losses are often negligible; for short runs with many fittings they can dominate. An alternative is the equivalent-length method, adding L_eq = K·D/f to the pipe length.

Component	K
Re-entrant / projecting pipe entrance	0.8–1.0
Sharp-edged (flush) entrance	0.5
Slightly rounded entrance (r/D ≈ 0.1)	0.2–0.25
Well-rounded entrance (r/D ≥ 0.15)	0.04–0.05
Exit (pipe → reservoir), any shape	1.0

Component	Threaded	Flanged
90° elbow, regular (standard)	0.9	0.3
90° elbow, long radius	0.6	0.2
45° elbow, regular	0.4	0.2
180° return bend	1.5	0.2
90° bend, smooth (r/D = 4–6)	0.15–0.30
Mitered bend, 90° (no vanes)	1.1–1.3

Component	Threaded	Flanged
Tee, line (run-through) flow	0.9	0.2
Tee, branch flow	2.0	1.0

Valve type	K
Ball valve, full bore	0.05
Gate valve	0.15–0.2
Butterfly valve	0.3–1.2
Swing check valve	2.0–2.5
Angle valve	2–5
Globe valve	6–10
Foot valve with strainer (hinged)	0.8–1.5

Component	K (based on smaller-pipe velocity)
Sudden expansion	K = (1 − A₁/A₂)² = (1 − (d₁/d₂)²)²
Sudden contraction	K ≈ 0.5(1 − A₂/A₁) (0 for no change, 0.5 for exit into pipe)

Minor Loss Coefficients (K) — Reference

Entrances & Exits

Bends & Elbows

Tees

Valves (Fully Open)

Sudden Expansion & Contraction

Related cheat sheets and tools