[Steam-engine] Safety valves

[Bruce & Marlene Babcock]

Ken,

    You said your safety valves blow down 5 or 6 psi.

    At 5 psi your 140 psi safety valves would blow down 3.6% and your 145 psi valve 3.4%.

    At 6 psi the figures would be 4.3% and 4.1%. 

    If you were to  purchase new valves that blow down 6% the 140 psi valve would blow down 8.4 psi and the 145 valve would blow down 8.7 psi. 

    I wish I had copies of the ASME codes published between 1983 and 2001 so I could determine when they increased the blowdown to 6%.   I suspect you purchased your valves before that change occurred.   If you simply replaced your existing valves and did not specify 4% blowdown and received valves set at 6% you might be disappointed in their performance. 

    Your satisfaction with valves set at 3.4% to 4.3% blowdown is consistent with what owners and operators have reported.  Your experience certainly supports the idea that safety valves with lower blowdowns are more satisfactory.   I hope others will report their experiences just as you have. 

    Thanks,

Bruce E. Babcock