Max Working Pressure

Maximum working pressure will be dependant on working temperature, and whether you are dealing with a liquid or with steam.

Ask the valve distributer or manufacturer for a pressure/temperature chart to determine to working pressure for your specific situation.

Nominally the 800# valve means 800 PSI rating, but it might vary. Check with the manufacturer, not with some anonomous poster you don't know on the internet!

You know, if you had the max working temperature to hand you would have all the information you need to make a phone call to your local friendly valve distributor, and ask.