When you have a question about process automation that needs a short answer, let us know with #WishIknew and @Visaya! We’ll reply with a #WishIknew post. It’ll give a quick explanation, then some related articles, videos, or reviews if you want to know more.

### I wish I knew what control valve Cv means!

The Control valve Cv means the flow coefficient of the valve. It applies to the factor of the head drop (Δh) or pressure drop (ΔP) over a valve with the flow rate Q. The formula will differ depending on the product the valve regulates, such as liquid, gas, or steam.

Also, the Cv varies across control valves because each valve lets the flow pass through differently. The difference of Cv relates to the type of the valve and its opening position. When you need to scale out a valve for your application, you need the Cv to select the right valve.

Some vendors have standardized the flow coefficient (Kv). They created this standard using reference conditions, such as water at a specific temperature, flow rate, and drop pressure units. Keep in mind also that the Kv uses metric units and the Cv imperial units. Here’s the formula if you need it:

Kv = 0.865 · Cv
Cv = 1,156 · Kv

### I found ValveMan on the Tube of You, and he provides more details on this idea:

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