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Posted by Tom Stanton on May 01, 2002 at 11:31:18:
In Reply to: Test lifting relief valves accelerates deterioration? posted by Gern Blanston on April 30, 2002 at 18:52:55:
You ask a couple fo questions that have been debated for years. This is what I teach the students at Mass Maritime. Safety and relief valves should be tested prior to a boiler going on line and prior to the boiler coming off line. The ASME Codes recommend there be at least 75% of the set pressure acting on the valve prior to hand testing. I agree with this, particularly because the lift of the disc from its seat is only a fraction of an inch and you want to get a good flow through the valve. What if a boiler is to be in operation for months? Well, that is your call. Personally, I recommend testing them at least twice a year in that case. Hot water relief valves can be a bit of a pain in the butt. If they haven't been tested for months or years, and you test them, you better know where the water shut-off is because they will probably leak. If it is a new relief vavle, a couple of times a year will probably be sufficient. Believe it or not, safety and releif valves account for an extremely small amount of boiler accidents. Go on line at the National Board @ www.nationalboard.org and click on incident reports, you will find about 80% of the acidents are caused by low-water, operator error and poor maintenance.