Matching the valve¹s body material and end connection to existing piping or specifications is the best choice. Otherwise, to determine what body material and end connection you need, you must first know the pressure and temperature of the medium entering your valve. For most flowing media you will need an approximate idea of the temperature. For saturated steam you can use the steam table below to determine the temperature. Once you know the pressure and temperature, you can use the body pressure-temperature rating table, (to right, to determine what body material and end connection you need. You need a 2-1/2 inch single-seated valve. You have saturated steam entering your valve at 100 PSIG. From the steam table you see the steam has a temperature of 337.9°F. From the valve configuration sheets you know that a 2-1/2 inch single-seated valve is available with an iron body with a 125 flange or an iron body with a 250 flange. Scanning the pressure-temperature rating table, you see that the pressure rating for an iron body with a 125 flange at 337.9°F is not listed but a pressure rating is listed at 350°F. At 350°F the pressure rating is 125 PSIG. Since 350°F exceeds the actual temperature of 337.9°F and the 125 PSIG rating at 350°F exceeds the actual pressure of 100 PSIG, an iron body with a 125 flange is ok. You need a 6 inch double-seated valve. You have 200 PSIG water entering your valve at 175°F. From the valve configuration sheets you know that a 6 inch double seated valve is available with an iron body with a 125 flange or an iron body with a 250 flange. Scanning the pressure-temperature rating table, you see that the pressure rating for an iron body with a 125 flange at 175°F is 170 PSIG. Since this pressure rating is less than the actual pressure rating of 200 PSIG, an iron body with a 125 flange is not ok. Scanning the pressure-temperature rating table again, you see that the pressure rating for an iron body with a 250 flange at 175°F is 385 PSIG. Since this 385 PSIG rating is greater than the actual pressure of 200 PSIG, an iron body with a 250 flange is ok.