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Cv Flow Coefficients of Gate Valves
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AlternarCv Flow Coefficients of Gate Valves
O Cv (Flow Coefficient) of a valve measures its flow capacity under specific conditions. It is a critical parameter for selecting the right valve size and predicting pressure drop.
1. Definition of Cv
O Cv value is defined as:
The number of US gallons per minute (GPM) of water at 60°F that will pass through a fully open valve with a pressure drop of 1 psi.
Formula:
Cv=QSGΔPCv=QΔPSG
Where:
Q = Flow rate (GPM)
SG = Specific gravity of the fluid (1 for water)
ΔP = Pressure drop (psi)
2. Typical Cv Values for Gate Valves
Gate valves have high Cv values because they offer minimal flow restriction when fully open. Below are approximate Cv ranges for different sizes:
| Valve Size (inches) | Cv (Full Port) | Cv (Standard Port) |
|---|---|---|
| ½” | 15 – 20 | 10 – 15 |
| 1″ | 35 – 50 | 25 – 35 |
| 2″ | 120 – 150 | 80 – 100 |
| 4″ | 450 – 600 | 300 – 400 |
| 6″ | 900 – 1,200 | 600 – 800 |
| 8″ | 1,600 – 2,000 | 1,000 – 1,400 |
| 10″ | 2,500 – 3,200 | 1,600 – 2,200 |
| 12″ | 3,600 – 4,500 | 2,400 – 3,000 |
| Size | Size | Classe 150 | Class 300 | Class 600 | Class 900 | Classe 1500 | Classe 2500 | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| NPS | DN | Velan | Ringo Valvulas | Australian Pipeline Valve | Velan | Ringo Valvulas | Australian Pipeline Valve | Velan | Ringo Valvulas | Australian Pipeline Valve | Velan | Ringo Valvulas | Australian Pipeline Valve | Velan | Ringo Valvulas | Australian Pipeline Valve | Velan | Ringo Valvulas | Australian Pipeline Valve |
| 2 | 50 | 260 | 200 | 311 | 260 | 200 | 311 | 260 | 200 | 311 | 230 | 155 | 273 | 230 | 200 | 273 | – | 164 | 170 |
| 2½ | 65 | 420 | – | 495 | 420 | – | 495 | 420 | – | 495 | – | – | 397 | – | – | 397 | – | – | 273 |
| 3 | 80 | 625 | 710 | 72 | 625 | 710 | 72 | 625 | 710 | 724 | 560 | 650 | 665 | 510 | 600 | 604 | – | 275 | 397 |
| 4 | 100 | 1150 | 1300 | 1320 | 1150 | 1300 | 1320 | 1150 | 1300 | 1320 | 1050 | 1200 | 1239 | 925 | 1070 | 1078 | – | 460 | 660 |
| 6 | 150 | 2650 | 3100 | 3076 | 2650 | 3100 | 3076 | 2650 | 3100 | 3076 | 2400 | 2850 | 2815 | 2100 | 2500 | 2450 | – | 1100 | 1588 |
| 8 | 200 | 4850 | 5720 | 5608 | 4850 | 5720 | 5608 | 4850 | 5500 | 5434 | 4200 | 5025 | 4901 | 3650 | 4370 | 4244 | – | 1970 | 2815 |
| 10 | 250 | 7750 | 8940 | 8834 | 7750 | 8940 | 8834 | 7750 | 8485 | 8474 | 6750 | 7850 | 7817 | 5850 | 6850 | 6761 | – | 3130 | 4566 |
| 12 | 300 | 11500 | 13350 | 13071 | 11500 | 13350 | 13071 | 11500 | 12850 | 12509 | 9700 | 11500 | 11171 | – | 9980 | 9657 | – | 4535 | 6553 |
| 14 | 350 | 14000 | 16275 | 16074 | 14000 | 16275 | 16074 | 13000 | 15370 | 15151 | 12000 | 13900 | 13646 | – | 12000 | 11701 | – | 8368 | 8027 |
| 16 | 400 | 19000 | 21560 | 21554 | 19000 | 21560 | 21554 | 18000 | 20170 | 20106 | 16000 | 18150 | 18031 | – | 15675 | 15447 | – | 10955 | 10633 |
| 18 | 450 | 24000 | 28720 | 27876 | 23500 | 28790 | 27876 | 22000 | 26200 | 25406 | – | 23910 | 23056 | – | 20640 | 19766 | – | 14481 | 13646 |
| 20 | 500 | 31000 | 35760 | 35048 | 30000 | 34840 | 35048 | 27000 | 32100 | 31355 | – | 29550 | 28726 | – | 25880 | 25022 | – | 17587 | 16713 |
| 24 | 600 | 45000 | 52165 | 51973 | 44000 | 51050 | 51973 | 40000 | 46750 | 46312 | – | 42570 | 42027 | – | 31175 | 36507 | – | 21338 | 24610 |
| 26 | 650 | 53000 | 63500 | 61714 | 53000 | 62011 | 61714 | 38000 | 56300 | 54333 | – | 52167 | 49668 | – | 45514 | – | – | – | – |
| 28 | 700 | 62000 | 74800 | 72387 | 62000 | 73046 | 72387 | 52000 | 65900 | 63023 | – | 60500 | – | – | 53320 | – | – | – | – |
| 30 | 750 | 73000 | 86325 | 83919 | 73000 | 84765 | 83919 | 82500 | 75520 | 73110 | – | 69452 | – | – | 61095 | – | – | – | – |
| 32 | 800 | 81000 | 103000 | – | 81000 | 100580 | – | – | 85180 | – | – | 79092 | – | – | 73478 | – | – | – | – |
| 34 | 850 | 92500 | – | – | – | – | – | 82500 | – | – | – | – | – | – | – | – | – | – | – |
| 36 | 900 | 108000 | 129500 | 119333 | 108000 | 125825 | 119333 | 72000 | 114250 | 114881 | – | 103212 | – | – | 96862 | – | – | – | – |
| 38 | 950 | 11500 | – | – | – | – | – | 103000 | – | – | – | – | – | – | – | – | – | – | – |
| 40 | 1000 | 130000 | 175860 | – | 129500 | 171740 | – | 115000 | 156127 | – | – | – | – | – | – | – | – | – | – |
| 42 | 1050 | 142000 | 223300 | 163380 | 129500 | 217000 | 163380 | – | 197272 | – | – | – | – | – | – | – | – | – | – |
| 44 | 1100 | – | – | – | – | – | – | 144000 | – | – | – | – | – | – | – | – | – | – | – |
| 46 | 1150 | 171000 | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – |
| 48 | 1200 | 190000 | 335500 | 215888 | – | 326000 | 215888 | – | – | – | – | – | – | – | – | – | – | – | – |
| 50 | 1250 | 198000 | – | – | – | – | – | 190000 | – | – | – | – | – | – | – | – | – | – | – |
| 54 | 1350 | 238000 | – | 278938 | – | – | 278938 | – | – | – | – | – | – | – | – | – | – | – | – |
| 56 | 1400 | 260000 | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – |
| 60 | 1500 | 300000 | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – |
| 64 | 1600 | 340000 | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | – | |
Notes:
Full port (full bore) gate valves have a higher Cv because their bore matches the pipe ID.
Standard (reduced) port gate valves have a slightly smaller bore, reducing Cv by ~20-30%.
Cv increases with valve size due to larger flow area.
3. Factors Affecting Cv
Valve Design
Full port vs. standard port
Wedge type (solid, flexible, split)
Flow Conditions
Turbulent vs. laminar flow
Viscosity effects (higher viscosity reduces Cv)
Pressure Drop (ΔP)
Higher ΔP increases flow rate but may cause cavitation.
Fluid Properties
Specific gravity (SG) and temperature affect Cv.
4. Calculating Required Cv for a System
To select the right valve size, engineers calculate the required Cv based on system conditions:
Cv=QΔPSGCv=SGΔPQ
Example Calculation:
Flow rate (Q): 100 GPM
Pressure drop (ΔP): 5 psi
Specific gravity (SG): 1 (water)
Cv=10051=1002.236≈44.7Cv=15100=2.236100≈44.7
UM 2″ full-port gate valve (Cv ≈ 120-150) would be more than sufficient.
5. Comparing Cv with Other Valve Types
| Tipo de válvula | Typical Cv (2″ Valve) | Flow Efficiency |
|---|---|---|
| Válvula de gaveta | 120 – 150 (full port) | Muito alto |
| Válvula de esfera | 150 – 200 (full port) | Alto |
| Válvula globo | 30 – 50 | Moderate |
| Válvula borboleta | 80 – 120 | Alto |
Key Takeaway:
Gate valves have excellent flow capacity (high Cv) but are not ideal for throttling.
Ball and butterfly valves may have slightly higher Cv but serve different purposes.
6. Industry Standards for Cv Testing
ANSI/FCI 70-2 – Standard for control valve flow coefficients.
ISA-75.01.01 – Flow equations for sizing control valves (sometimes referenced for manual valves).
ISO 5208 – Industrial valve testing (includes leakage and flow capacity checks).
Conclusão
O Cv value is crucial for selecting the right gate valve size to minimize pressure drop and ensure efficient flow. Full-port gate valves offer the highest Cv, making them ideal for low-resistance applications.
