Hi Doug.
Good to see you running with the boiler. I am glad you have some satisfactory insulation, as it is a fundamental part of the Engineering, and was first applied by Newcomen, when he made his first major improvement to his atmospheric steam engine to improve efficiency.
His original engine filled the cylinder with steam, heating all the metal on the way, then he sprayed water into the cylinder to create the vacuum that permitted the atmosphere to do the work of lifting water from the mines. In his major improvement he then lagged the cylinder when he added a separate condenser, that created the vacuum, and was connected by a valve to the working cylinder. So lagging the cylinder was a very early introduction to the system engineering. Boilers became lagged soon after, as did interconnecting pipework. All long before Trevethick and his use of high pressure steam.
I realise that you are using a temporary steam connection, in the plastic hose from boiler to engine.
Please will you consider a safer connection by using a lagged metal steam pipe, or at least an hydraulic hose certified for the temperature and pressure of your boiler, that can carry the steam safely. NOT PLASTIC!
I cannot repeat enough that STEAM IS A DANGEROUS MEDIUM.
The plastic pipe will soon stretch, weaken and fail, as it cannot take the temperature and pressure for very long. When it bursts, you will have a flapping hose waving steam directly from the boiler, as it rapidly loses all the steam. This steam will have an invisible part before the visible condensate plume, which will be the equivalent of a flame and can cause severe scalding if/when it hits flesh. And I don't want to hear your screams....
Any incidental damage to the boiler while rapidly depressurising won't be your biggest problem, as the boiler is probably strong enough to withstand the rapid stress changes.
I know someone who has permanent scars from scalding. Not nice. Hospital, 3 months off work.... skin grafts, the lot! Your boiler has the stored energy to do that...
Sorry to "preach" about safety, but you MUST work safely, and demonstrate Safe Working Practice on anything you publish on a public domain, such as your videos on this site. Innocent people copy what we show and advise, and I don't want anyone getting hurt. Equally, I would hope that anyone who spots my errors would tell me immediately, so I can correct them.
I use regular copper tubing, even as small as 1/8" bore, that is cheap enough from brake tube suppliers, caravan gas fittings suppliers, etc. And I use proprietary 1/8" BSP fittings, or larger, depending on the tube, (or modern metric equivalents). Lagging is simple cotton string wound around the pipework, then painted with white household emulsion, that gives a good representative finish to the model pipework and reduces the condensate in the wet steam.
Incidentally, you can see the condensate in the tubing, which should be avoided as much as possible. This is "wasted heat". Also there is a lot of further condensation produced inside the cylinder as the steam expands. All the condensate has to be purged at each stroke, but a build-up inside the cylinder is not only wasteful, especially when it sucks-in a blob of water from the condensate in the feed-pipe, but can cause an hydraulic lock, which stops the engine dead in a single stroke. This can cause damage such as buckling of rods or hammering of bearing bronzes, as the energy in the flywheel has to be instantly lost somewhere as with a hammer hitting metal on an anvil!
You may have felt some hydraulic locking when applying the steam initially, when you should apply it with just a cracked valve, and turn the engine by hand until it has warmed through on both strokes. You can damage an engine by whacking the steam valve wide open onto a cold engine. I saw it on a TV programme once, where the con-rod was bent by the operator doing just that! (A highly qualified mechanical engineering graduate without "steam" training!). The engineer couldn't figure what stopped the engine -dead. But it was water from condensed steam.... that drained away when the engine stopped. - Probably only filling the last tenth of the stroke, after the exhaust valve cut-off...
Hope that helps?
K2