Rules of thumb
Rules of thumb from practice – checked
Sentences passed on from colleague to colleague: short, memorable and sometimes wrong. For each rule this section says where it comes from, what is technically correct and where it ends.
The traffic light says how far a rule carries: green means it applies, amber means it applies under conditions, red means it is wrong as a general rule.
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Class 150 is not 150 psi – what the ASME pressure class really means
Class 150 does not mean 150 psi.
applies
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PN 16 is not always 16 bar – nominal pressure, temperature and material
PN 16 does not mean: always 16 bar.
applies
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DN is not a diameter – why DN 50 never measures 50 mm
DN is a nominal size – not a measurement.
applies
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Eccentric reducer: flat side on top – when the rule applies and when it does not
Eccentric reducer at the pump suction: flat side on top.
applies under conditions