When did the Kylchap exhaust patent expire?

[Harvester]

Just wondering when Andre Chapelon’s patent expired on the Kylchap exhaust system. Thompson fitted them to his Pacifics , so it would seem prior to 1945. IIRC the LNER was very reluctant to pay the patent fees, and only did so for the last four A4s built and one A3.

 

[MarkyT]

Just wondering when Andre Chapelon’s patent expired on the Kylchap exhaust system. Thompson fitted them to his Pacifics , so it would seem prior to 1945. IIRC the LNER was very reluctant to pay the patent fees, and only did so for the last four A4s built and one A3.

I believe it was 1941. Dad told me the figures for licensing the tech and employing the mandated consultants to do the calculations for the application equated to about 10% of the cost of an entire new pacific locomotive before WW2. Post-war, when the pacifics were being retrofitted en masse, Doncaster managed to drastically simplify the design and got the entire job to under £200 at next overhaul for an A3 and a little more for an A4. The process was described as 'undo four bolts and cut a larger hole in the top of the smokebox'! Dad made the business case easily for the A3s on coal savings alone after trials he arranged while at Top Shed.

 

[Harvester]

I believe it was 1941. Dad told me the figures for licensing the tech and employing the mandated consultants to do the calculations for the application equated to about 10% of the cost of an entire new pacific locomotive before WW2. Post-war, when the pacifics were being fitted en masse, Doncaster managed to drastically simplify the design and got the entire job to under £200 at next overhaul for an A3 and a little more for an A4. The process was described as 'under four bolts and cut a larger hole in the top of the smokebox'! Dad made the business case easily for the A3s on coal savings alone after trials he arranged while at Top Shed.

Thanks. That explains why the Thompson and Peppercorn Pacifics had them fitted when built, while the Gresley Pacifics were not treated until late in their careers.

Your Dad’s identity has just clicked. He did a great job during his time at Top Shed.