The Paragon-Cristiani Compressed Steam System was a Diesel-steam hybrid that used the steam for power transmission rather than power generation. The actual prime mover was intended to be a Diesel engine. It was based on patents held by Severino Cristiani and Secondo Sacerdole of Italy, and was promoted in England by Captain William Peter Durtnall.

Water is not boiled directly- instead the exhaust from a standard pair of cylinders is compressed by the Diesel engine, stored in an HP reservoir and released back to the cylinders by the regulator. Presumably distilled water was used in the circuit to prevent scale formation.
This is a vapour recompression scheme as used in the Holcroft-Anderson Recompression Locomotive.

The system was tested by adding two "Paragon" marine petrol engines to a converted 0-6-0ST locomotive built by Hawthorn Leslie in 1923.

Above: The steam circuit of the Cristiani Compressed Steam System. This appears to be the intended final version with a single Diesel engine driving the compressor. There seems to be something missing here- there is no steam exit from the HP reservoir, if the flow direction arrows are taken literally.

On trials it was at once clear that the HP steam reservoir was far too small, and it was augmented by putting the steam storage tank of a fireless locomotive on a four-wheeled chassis coupled behind the loco and plumbing it into the steam circuit. (Heath Robinson would have been proud to illustrate this, I am sure)
No details of the test results appear to survive, but the results cannot have been too encouraging as no more experiments of this sort were done in Britain. The 0-6-0 chassis (original works number 3513/1923) was converted back to a conventional 0-6-0ST named "Stagshaw". After a further career at Shotton colliery, the locomotive has been preserved on the Tanfield Railway.

Left: "Stagshaw" in steam on The Tanfield_Railway

OTHER COMPRESSED STEAM SYSTEMS
Though a 2-6-0 steam-compression loco with a 450hp Diesel was built by Krauss in Germany in 1926-7, and an even bigger 2-8-2 was planned) On completion of testing the machine was dismantled and was converted to an ordinary 0-6-0 tank engine. No further information on this has so far been found.

There is an obvious snag with any compressed-steam system. How do you start it from cold? With no steam to compress you can't put any energy into the steam circuit. A small oil-fired boiler had to be provided to raise the initial charge of steam, by indirectly heating both reservoirs with heating coils. This must have been an unwelcome complication.

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