Valve headloss comparison: For fully open valves, how does the loss coefficient compare for a gate valve versus a globe valve, and what is a typical magnitude?

Introduction / Context:Designers often use valve loss coefficients (K) or equivalent lengths (L_e/D) to estimate pressure drops in piping networks. This question benchmarks the relative headloss for fully open gate and globe valves, which is crucial in pump sizing and energy audits.

Given Data / Assumptions:

• Valves are fully open, clean, and in turbulent service.
• Gate valves present a nearly straight-through path; globe valves force the flow to turn, causing larger losses.
• Losses expressed as K (dimensionless) or as equivalent length L_e/D are standard approximations.

Concept / Approach:Fully open gate valves typically have very low K values—only a small fraction of those for globe valves. Globe valves, with tortuous flow paths, exhibit significantly higher losses. A commonly used order-of-magnitude for a fully open gate valve is a single-digit L_e/D, whereas globe valves can be orders of magnitude larger, reflecting much higher K values.

Step-by-Step Solution:

Verification / Alternative check:Standard headloss tables show fully open gate valves with small K and L_e/D values (single digits), and globe valves with much larger values, validating the order-of-magnitude statements.

Why Other Options Are Wrong:

• (a) is opposite of reality; gate valves are not more lossy than globe valves when fully open.
• (b) captures the relative magnitude (much less).
• (c) gives a representative single-digit figure often cited for a fully open gate valve’s equivalent length.

Common Pitfalls:Confusing throttling (partially open) behavior with fully open behavior; globe valves are intended for throttling and remain lossy even fully open, while gate valves are intended primarily for on/off service.

Final Answer:Both (b) and (c).