Wikipedia:Reference desk/Archives/Science/2022 April 19

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April 19

Short cutoffs

When driving a steam train at high speed, how can you tell if you've set the cutoff too short? I do know that the effect of this, in physical terms, is a "checking action" where the steam cannot fully exhaust to the blastpipe and creates a pressure cushion in the cylinders -- but my question is, how does this manifest itself in terms of sound and/or feel (sharper exhaust blasts, increased shaking, etc.)? And is the sound/feel in this case different with Stephenson valve gear than with Walschaerts? 2601:646:8A81:6070:8D25:F11A:29AC:2783 (talk) 00:05, 19 April 2022 (UTC)

Surely a longer cutoff would supply too much steam to the cylinders; a short cutoff would supply less? See Cutoff (steam engine). (Would that I had the experience to actually answer the question!) -- Verbarson  ^talk_edits 10:04, 19 April 2022 (UTC)

Not my field, but I found Explaining 'Cut Off' on a rail enthusiasts' blog, which may help. Alansplodge (talk) 13:02, 19 April 2022 (UTC)

Just read it, but it only explains what a cutoff is (which I already know), and the (rather obvious) effects of having it set too long while cruising at speed -- wasted steam and coal (and reduced performance due to lack of steam available), fire-throwing with consequent emissions of excessive smoke (harmful to the environment, could be dangerous in tunnels) and possibly sparks (fire hazard), and with a lever reverse also possible injury to the engineer if he tries to adjust it and it flies open uncontrollably under steam pressure -- but what it does not cover is what happens if the cutoff is set too short while cruising under power. 2601:646:8A81:6070:2152:CE20:4F73:F64E (talk) 09:14, 20 April 2022 (UTC)

@User:Verbarson: True, but a short cutoff also gives the steam less time to exit the cylinder to the blastpipe during the exhaust phase -- this is why setting it too short can lead to a checking action which reduces speed. 2601:646:8A81:6070:2152:CE20:4F73:F64E (talk) 09:17, 20 April 2022 (UTC)