Determine the diameter of the pipe if it is not already known. Measure the pipe with calipers or a tape measure if necessary.
Determine the resistance coefficient of the pipe, which is denoted as K. According to "Pump Characteristics and Applications" by Michael Volk, the value for K is available in tables based on the valve or fitting. The resistance coefficient K is also available from vendor as part of the valve's performance specifications.
Find the square root of K, the resistance coefficient of the pipe.
Square the value of the pipe diameter. Then multiply that value by 29.9.
Divide the result of Step 4 by the square root of K found in Step 3. The result is the valve flow coefficient Cv.
Things You Will Need
- The type of valve design or the valve coefficient of resistance
- Diameter of the pipe or a means to measure the diameter
- Larger diameter valves have a larger volumetric capacity and thus a larger Cv rating.
- According to "Practical Fluid Mechanics for Engineering Applications" by John J. Bloomer, the resistance coefficient for a sharp edged inlet is 0.5 while an inward projecting pipe has K = 1.0.