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In most cases, the materials of construction are specified by the customer and are determined by the chemical and physical properties of the process fluid, such as its corrosive nature, flowing pressure and/or temperature. Generally speaking, low pressure and low temperature water and steam applications use brass or cast iron bodies with brass or stainless steel trim. Steel is used for high temperature water and steam applications and for practically all flammable materials, such as lube oil. Stainless steel is usually chosen when the process fluid is corrosive or consists of food products.
Tables 1.1 and 1.2 show the maximum inlet pressure for a given material and body rating at a specific service temperature. Note that pressures greater than the body rating are permitted depending on the temperature of the process.
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Table 1.1 – Pressure (PSI) – (°F)
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Service
Temp (°F)
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Cast Iron
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––––––––– Cast Carbon Steel –––––––––
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125 lb.
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150 lb.
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300 lb.
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600 lb.*
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-20
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200
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285
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740
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1480
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0
|
200
|
285
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740
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1480
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100
|
200
|
285
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740
|
1480
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150
|
200
|
270
|
705
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1415
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200
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190
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260
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675
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1350
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250
|
175
|
245
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665
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1330
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300
|
165
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230
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655
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1315
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350
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150
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215
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645
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1285
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400
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140
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200
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635
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1270
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450
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125
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185
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615
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1235
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500
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–
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170
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600
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1200
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550
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–
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155
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575
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1145
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600
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–
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140
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550
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1095
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650
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–
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125
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535
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1075
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700
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–
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110
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535
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1065
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750
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–
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95
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505
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1010
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800
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–
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85
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410
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825
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*600 lb. Class may vary from ANSI standard – consult factory.
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Table 1.2 – Pressure (PSI) – (°F)
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Service
Temp (°F)
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––––––––––– Stainless Steel –––––––––––
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150 lb.
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300 lb.
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600 lb.*
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-20
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275
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720
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1440
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0
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275
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720
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1440
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100
|
275
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720
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1440
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150
|
260
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675
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1340
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200
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240
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620
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1240
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250
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225
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590
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1180
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300
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215
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560
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1120
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350
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205
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540
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1075
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400
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195
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515
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1030
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450
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180
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500
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1005
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500
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170
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480
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995
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550
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165
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465
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930
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600
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140
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450
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905
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650
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125
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445
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890
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700
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110
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430
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865
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750
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95
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425
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845
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800
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80
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415
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830
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*600 lb. Class may vary from ANSI standard – consult factory.
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The valve trim includes the plug, seat ring, cage, stem and the bushing. The valve plug and seat ring are the most susceptible to erosion damage caused by the impingement of high velocity particles. Table 3 shows the pressure and temperature limitations for stainless steel trim.
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Table 2 – Material Differential Pressure Limitation (P)
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Material
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Limit
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Trim Material (Plug/Seat/Bushing)
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316/316/440c
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200 psi
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17-4/17-4/440c
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*
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316 stellited/316 stellited/440c
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*
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*Use maximum recommended working pressure/temperature table.
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Table 3 – Material Temperature Limitation -50° to 750°F
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Material
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Limit
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Trim (Plug/Seat/Bushing)
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316/316/440c
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-50° to 600°F
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17-4/17-4/440c
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-40° to 600°F
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316 stellited/316 stellited/440c
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-50° to 750°F
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Refer to the Selection Guide Matrix for the style of trim and trim materials for
each valve type.
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