Table 17 ALLOWABLE PRESS. DROP RATINGS FOR UNBALANCED TRIM TEFLON PACKING, FLOW UP, No.12 Direct Actuator, 3 to 15 psi Spring
Air Supply Pressure 18 18 18 20 20 20 22 22 22 24 24 24 27 27 27 30 30 30 33 33 33 36 36 36
Leakage Class II IV & VI V II IV & VI V II IV & VI V II IV & VI V II IV & VI V II IV & VI V II IV & VI V II IV & VI V
.187" 6,487 6,060 4,140 >10000 >10000 9,210 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000
Allowable Pressure Drops (PSI) Trim Size .250" .375" .500 .750 3,609 1568 862 365 3,289 1355 702 259 1,849 395 6,461 2,836 1,575 682 6,141 2,626 1,415 576 4,701 1,663 695 96 9,313 4,104 2,288 999 8,993 3,890 2,128 893 7,553 2,930 1,408 413 >10000 5,371 3,001 1,316 >10000 5,158 2,841 1,209 >10000 4,198 2,121 729 >10000 7,272 4,071 1,791 >10000 7,059 3,911 1,685 >10000 6,099 3,191 1,205 >10000 9,174 5,140 2,267 >10000 8,961 4,980 2,160 >10000 8,001 4,260 1,680 >10000 >10000 6,210 2,742 >10000 >10000 6,050 2,635 >10000 9,902 5,330 2,155 >10000 >10000 6,923 3,059 >10000 >10000 6,763 2,952 >10000 >10000 6,043 2,472
1.000 196 116 374 294 552 472 112 730 650 290 998 918 558 1,265 1,185 825 1,532 1,452 1,092 1,711 1,631 1,271
Usually direct acting actuators use a 3-15 psi spring. With an 18 psi air supply pressure, there is a 3 psi (18-15=3) net closure force on the trim, or for a 27 psi supply the net closure force is 12 psi. If a 6-30 psi spring is used in a direct acting actuator, add 15 to pressure in the air supply column.
Initial Air Pressure 3 3 3 6 6 6 9 9 9 12 12 12
ALLOWABLE PRESS. DROP RATINGS FOR UNBALANCED TRIM TEFLON PACKING, FLOW UP, No.12 Reverse Actuator Allowable Pressure Drops (PSI) Leakage Trim Size Class II IV & VI V II IV & VI V II IV & VI V II IV & VI V
.187" 6,487 6,060 4,140 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000 >10000
.250" 3,609 3,289 1,849 7,887 7,567 6,127 >10000 >10000 >10000 >10000 >10000 >10000
.375" 1,568 1,355 395 3,470 3,256 2,296 5,371 5,158 4,198 7,272 7,059 6,099
.500 862 702
.750 365 259
1.000 196 116
1,932 1,772 1,052 3,001 2,841 2,121 4,071 3,911 3,191
841 734 254 1,316 1,209 729 1,791 1,685 1,205
463 383 23 730 650 290 998 918 558
The Initial air pressure is actuator diaphragm pressure when the valve begins to open. For example, a 315 has an initial pressure of 3 psi. The spring may have additional compression to provide the 6, 9 & 12 psi initial pressures.
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10/10/2008