|
Flow velocity in control valves |
| It is recommended that the maximum inlet flow velocities applied to control valves should be as shown in the tables below. | |||||
|---|---|---|---|---|---|
| Globe Valves Size | Liquid | Steam or Gas | |||
| mm | inch | m/s | ft/s | m/s | ft/s |
| 15 - 25 | 1/2 - 1 | 9 | 30 | 120 | 400 |
| 40 - 50 | 1 1/2 - 2 | 7.5 | 25 | 90 | 300 |
| 65 - 100 | 2 1/2 - 4 | 6 | 20 | 75 | 250 |
| 150 - 200 | 6 - 8 | 6 | 20 | 70 | 225 |
| 250 - 400 | 10 - 16 | 4.5 | 15 | 55 | 175 |
| Angle Valves Size | Liquid | Steam or Gas | |||
| mm | inch | m/s | ft/s | m/s | ft/s |
| 15 - 25 | 1/2 - 1 | 13.5 | 45 | 135 | 450 |
| 40 - 50 | 1 1/2 - 2 | 12 | 40 | 105 | 350 |
| 65 - 100 | 2 1/2 - 4 | 10.5 | 35 | 90 | 300 |
| 150 - 200 | 6 - 8 | 9 | 30 | 85 | 275 |
| 250 - 400 | 10 - 16 | 7.5 | 25 | 70 | 225 |
| Not only the tables maximum inlet flow velocities applied to a control
valve is important. A control valves' opening characteristic is also very
important for the smooth function of the entire control loop. LINEAR (Flow is directly proportional to the plug lift.) Use this trim characteristic if the difference pressures over the control valve differ less than 20%. EQUAL PERCENTAGE (With unit change in plug lift, the flow changes by a constant percentage of its instantaneous value.) Use this trim characteristic if the difference pressures over the control valve differ more than 20%. The equal percentage trim characteristic is also the best when the sizing data is a little uncertain and the valve may be oversized. QUICK OPENING (Capacity increases rapidly in linear relationship with plug lift, reaching maximum value with small opening travel.) A plug-lift equal to a quarter of the plug diameter gives full passage. |
©2007 Lars Josefsson Steamesteem in a computerized world
Marine steam boilers today and yesterday.
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