There has been much talk of design, testing, operation, etc. of boilers in our hobby. Back in 2004 The Northwest Steam Society put out a booklet entitled Guidelines for Operating Safety in our HOBBY, known as "G.O.S.H". This small booklet was put together using recommendations by skilled, knowledgeable, professional people in our hobby. There is good information on piping, valves, blowing down the gauge glass, boiler testing, and many other items. I would strongly suggest that serious hobby steamboaters get a copy and read it, particularly the boiler testing procedures - as approved by the ASME (American Society of Mechanical Engineers) and the NBIC (National Board Inspection Code) - to make sure irrepairable damage is not done to the boiler and its appendages during testing! You can view it and download it at: http://www.northweststeamsociety.org/Pa ... -FINAL.pdf at no charge. 
to ask!! Den