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[hades_lear]

Hi!

I am confused when trying to understand the following pharagrap which talks about the set pressure for PSV in boilers.

 

PG-67.3
 

""One or more safety valves on the boiler proper shall be set at or below the maximum allowable working pressure (except as noted in PG-67.4). If additional valves are used the highest pressure setting shall not exceed the maximum allowable working pressure by more than 3%. The complete range of pressure settings of all the saturated-steam safety valves on a boiler shall not exceed 10% of the highest pressure to which any valve is set. Pressure setting of safety relief valves on high-temperature water boilers20 may exceed this 10% range.""

 

I do not understand completely it. What this standard means with "The complete range of pressure settings of all the saturated-steam safety valves on a boiler shall not exceed 10% of the highest pressure to which any valve is set. Pressure setting of safety relief valves on high-temperature water boilers20 may exceed this 10% range"?

 

Any suggestion?

 

Thanks so much!

 

 

 

 

[fallah]

hades_lear,

 

Let's go through an example:

 

Suppose MAWP of a boiler to be 100 barg and the highest pressure to which last valve (among several ones) is set would be 103 barg, then "the complete range of pressure setting" of all PSV's on the steam boiler would be between 92.7 barg and 103 barg; means lowest pressure setting cannot be lower than 92.7 barg (103-0.1*103). Actually this limited range is specified to prevent PSV's set pressures to be so close to boiler operating pressure and keeping a reasonable margin between PSV setting and boiler operating pressure.

Of course, for high-temperature water boiler the range may exceed 10% due to possibility of PSV's interference arises from high blowdown characteristics of the liquid relief PSV's.