Straight Through Diaphragm Valves - Flow Coefficients
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Typical flow coefficients - Cv - and flow factors - Kv - for diaphragm straight through flanged cast iron valves of "Saunders" type:
| Valve Size | Unlined | Rubber Lined | Glass/Plastic Lined | ||||
|---|---|---|---|---|---|---|---|
| DN | Inches | Cv | Kv | Cv | Kv | Cv | Kv |
| 15 | 1/2 | 9 | 7 | 9 | 8 | ||
| 25 | 1 | 38 | 33 | 31 | 26 | 39 | 34 |
| 32 | 1 1/4 | 56 | 48 | 46 | 39 | 58 | 50 |
| 40 | 1 1/2 | 75 | 65 | 66 | 57 | 79 | 68 |
| 50 | 2 | 128 | 110 | 107 | 92 | 138 | 119 |
| 65 | 2 1/2 | 238 | 205 | 195 | 168 | 254 | 219 |
| 80 | 3 | 330 | 284 | 264 | 228 | 342 | 295 |
| 100 | 4 | 588 | 507 | 480 | 414 | 618 | 533 |
| 125 | 5 | 924 | 797 | 720 | 621 | 960 | 828 |
| 150 | 6 | 1 680 | 1 448 | 1 260 | 1 086 | 1 800 | 1 552 |
| 200 | 8 | 2 580 | 2 224 | 2 196 | 1 893 | 2 724 | 2 348 |
| 250 | 10 | 4 020 | 3 466 | 3 420 | 2 948 | 4 296 | 3 703 |
| 300 | 12 | 6 060 | 5 224 | 4 884 | 4 210 | ||
| 350 | 14 | 10 300 | 8 879 | 9 950 | 8 578 | ||
The opening and closing characteristic of the valves are close to positive linear:
- closing a valve to 80% - reduces the flow coefficient to approximately 85%
- closing a valve to 50% - reduces the flow coefficient to approximately 60%
This close to linear characteristic make the valves suited for adjustment and balancing operations. In addition the lined versions are able to resist wear and tear and rough environments and processes.
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