Flow Coefficients - Cv - and Flow Factors - Kv - of Straight Through Diaphragm Valves

Typical flow coefficients - Cv - and flow factors - Kv - of

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The table below indicates 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 9 7 9 8
25 1 38 33 31 26 39 34
32 1 56 48 46 39 58 50
40 1 75 65 66 57 79 68
50 2 128 110 107 92 138 119
65 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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