A BRIEF HISTORY OF SAFETY VALVES ON HANDS-FIRED BOILERS
The objective of safety valves for hands-fired boilers have altered from 1909 to today. A security valve from 1909 (left) was designed to give notice from the greatest pressure allowable, based on the American Society of Mechanical Engineers, and also to give alarm more water or fuel was needed. (See "The objective of a security Valve" in the finish want to know, to find out more.
At nearly every show I attend, I ask a couple of engine proprietors and operators if they're pleased with their new-style safety valves. It might be merely a small exaggeration to state which I get just two responses. "I have used a brand new-style valve for fifteen years and that I haven't had any problem with it" or "They are junk!" I've cleared up the 2nd reaction to spare the readers the uncomfortable expletives.
Because of these conversations, I've tried to realize why there's this type of discrepancy between your reactions to modern safety valves. It now seems there are a couple of easy steps we are able to take when choosing and installing these valves that may improve our satisfaction using the new-style valves, what are only ones presently available.
To know the problems active in the choice of a security valve, it's important to examine a brief history of safety valves utilized on hands-fired boilers. I'm talking about hands-fired boilers instead of historic boilers since the issues are based on the way the boilers are fired, not the way they are built or what their ages are. The needs for any modern welded boiler designed to the American Society of Mechanical Engineers (ASME) code overlap with for any 100-year-old riveted boiler, if both boilers are hand-fired. The needs for any safety valve for any boiler that's instantly fired are dramatically different.
With automatic firing, the security valve's work as based on Anderson Greenwood Crosby, a producer of contemporary safety valves, would be to safeguard existence and property if other safety precautions fail. A security valve on the hands-fired boiler, as based on ASME almost 100 years ago, would be to give notice from the greatest pressure allowable and also to give alarm more water or fuel is required. (The evolution of the objective of the security valve is summarized in "The objective of a security Valve," in the finish want to know,.)
When hands-fired boilers, for example, available on traction engines, steam cranes and locomotives disappeared, the majority of the boilers that continued to be instantly fired. The security valve manufacturers adapted their designs accordingly. That old-style valves with bottom led, beveled seats were able to withstand vibration and operating near their setpoint, and were substituted with smaller sized top-led valves with flat seats.
Simultaneously, steam system designs were adapted so there wasn't any have to operate within 10 % from the setpoint from the safety valve. Not every old-style valves had beveled seats, but those that didn't specify for much differently in the modern flat-sitting down valves.