Class of Valve

friend,

class means pressure rating of valves

#300 - 300psi (psi - pounds per square inch)

RF - Raised Face

in valves outlet connections may be flanged,screwed,socket weld and butt weld,according to customer requirements.

in flanged end connection flanges having raised face to arrest leak

To all whose reply :

Thank you so much for your kind response.Appreciate that so much!! :D

:P I learned more. Thanks you all

If you Google "pressure class ratings" you can find a number of publications that explain this. As PWSlack mentioned, the actual ratings of valves and flanges may differ from their nominal pressure class according to the temperature involved.

Look for standard ANSI B16.5 for a table "Pressure classes, size range - basic ratings for carbon steel flanges". For example: Class 300 means the flange will hold a pressure of 720 psi for non shock conditions at -20 to +100 deg F

3/4" or 3/4 inch refers to the size of valve. This means it is suitable for a pipe with a diameter of about 3/4 inch (19mm approx). This is not the exact size. You will find the exact size in the tables.

As for the pressure rating it is worth considering why a class 300 valve can operate at a higher pressure at ambient temperatures. A lot of the work on classifying valves was carried out a long time ago when the main requirement for high pressure valves was for steam boiler systems. A class 150 valve will be suitable for a pressure of 150 psi (pounds per square inch) when the steam is at saturation pressure at 150 psi. This is at a temperature of about 300 degrees Fahrenheit. If you use it at a lower temperature it is suitable for a higher pressure. Similarly a class 300 valve will be good for 300 psi at the temperature of saturated steam at 300 psi - I think this is about 600 deg F but you need to check. Again, if you use it at a lower temperature the steel strength is higher and it is good for a higher pressure. You will notice that the relationship is not linear - a class 300 flange or valve does not have exactly double the pressure rating of a class 150 valve/flange. Also, because the relationship between the strength of stainless and that of Carbon steel at elevated temperatures is different, you will find some differences in their ratings so nowadays it is better to look the values up in a table for the material you are using.

ejaquinn,

The 300# RF is the valve connection specification. The pipe connections will be flanged with raised faces for gaskets with thru bolting per pipe spec. for 300 Lb. pipe. The nominal pipe size is 0.75" as you know. The flow characteristics of the valve and shut off class is the next chapter for study.

Luther M

The 300# number is the pressure rating of the valve (in other words 300 psi)

Nope. See #2⇑.

Ya its right.... 300# denotes the pressure rating in terms of psig i,e pounds per square inches (gauge), if you divide it by 14.65, pressure will in terms of kg/cm^2. And the MOC of the valve body shows its applications at various temperatures. Mostly MOC of the steam valve is Carbon steel but for high temperatures (.500deg C), it will be of F22

Nope. See #2⇑.