What is the CV (flow coefficient) of the globe valves

What is the flow coefficient of a globe valve

The flow coefficient (Cv value) of a globe valve is usually between a few and dozens, and the specific value varies depending on the nominal diameter of the valve, the structure, the valve core type, the valve seat material and the processing accuracy. The following are some approximate ranges in common situations:

1. By nominal diameter

Small diameter globe valve: The Cv value of a small-diameter globe valve with a nominal diameter between 1/2 Inch (DN15) and 2 Inch (DN50) is generally between 2.5 and 20. For example, the Cv value of a 1/2 Inch (DN15) globe valve may be around 2.5 to 4, the Cv value of a 1 Inch (DN25) globe valve is about 6 to 10, and the Cv value of a 2 Inch (DN50) globe valve may be between 12 and 20.

Medium diameter globe valve: For medium-diameter globe valves with a nominal diameter of 2-1/2 Inch (DN65) to 6 Inch (DN150), the Cv value is usually between 20 and 60. For example, the Cv value of a 2-1/2 Inch (DN65) globe valve may be between 20 and 30, the Cv value of a 4 Inch (DN100) globe valve may be between 35 and 50, and the Cv value of a 6 Inch (DN150) globe valve may be between 45 and 60.

Large diameter globe valve: Large-diameter globe valves with a nominal diameter greater than 6 Inch (DN150) have relatively large Cv values, generally above 60 to 100. For example, the Cv value of a 8 Inch (DN200) globe valve may be between 80 and 100, and the Cv value of a 12 Inch (DN300) globe valve may be between 120 and 150 or even higher.

2. By structural form

Straight through globe valve: The Cv value is relatively high, generally at a medium level among globe valves of the same diameter. For example, the Cv value of a DN50 straight-through globe valve is about 10 to 15, and the Cv value of a DN100 straight-through globe valve may be 30 to 40.

Angle globe valve: Because its flow path is relatively tortuous and the fluid resistance is relatively large, the Cv value is slightly lower than that of a straight-through globe valve. The Cv value of a DN50 angle globe valve may be around 8 to 12, and the Cv value of a DN100 angle globe valve is about 25 to 35.

3. By valve core type

Flat valve core globe valve: The Cv value is relatively high, for example, the Cv value of a DN100 flat valve core globe valve may be 40 to 50.

Conical valve core globe valve: Due to the closer contact between the valve core and the valve seat, the sealing performance is better, but the fluid resistance is relatively large, and the Cv value is relatively low. The Cv value of the DN100 conical valve core globe valve may be between 30 and 40.

4. According to the valve seat material and processing accuracy

Metal valve seat globe valve: The metal valve seat has high hardness and good wear resistance, but the processing accuracy requirements are high. If the processing accuracy is high, the Cv value can reach a higher level of the same type of valve; if the processing accuracy is insufficient, the sealing surface may be uneven and the Cv value will be reduced. For example, the Cv value of the DN80 metal valve seat globe valve with high precision processing may be between 30 and 35, and the Cv value of the general processing accuracy may be between 25 and 30.

Soft valve seat globe valve: If soft materials such as polytetrafluoroethylene are used as valve seats, the sealing performance is good, but soft materials may deform under high temperature or high pressure, affecting the flow coefficient. A DN65 soft seated globe valve might have a Cv value of around 20 to 25.

Summary

The globe valve is an important flow control device. Its flow coefficient is an important parameter that describes its flow capacity and needs to be reasonably calculated and selected. Understanding the factors that affect the flow coefficient can help select the appropriate globe valve to ensure the normal operation of the system.