Posted by Carl on May 31, 2000 at 12:30:43:
In Reply to: Safety valves posted by Dave on May 24, 2000 at 09:11:51:
: On a boiler with two different size safety valves which should lift first,the larger or the smaller?Why?The boiler is rated @250 psi and 55000pph.Is there code to this effect?Thanks
Dave, It would be more cost effective to have the smaller valve lift first, not that the cost of a safety valve is necessarily linear with size. Most minor excursions would be taken by the smaller vale, orfice wise, and would then lessen the chance of the two of them operating at or close to their poping point wich results in chatter. There is no code other than the size of the smaller valve should be at least, memory here, 50% of the larger valve in capacity. I don't have a Code book at hand to verify that figure, so don't quote me just yet. Also, release of steam is a release of heat energy and the less you relieve to satisfy the overpressure the better.
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