Canadian Pacific class T4a

Number 8000 of the Canadian Pacific, also designated class T4a, was an experimental 2-10-4 high-pressure locomotive. It had a Schmidt-Henschel boiler that consisted of three circuits. The first one was located in the firebox and operated as a closed circuit with distilled water. Pressure was 1,350 psi or 93 bars. The second one, that also fed the central high pressure cylinder, was operated with 850 psi or 59 bars. The third circuit was located in the boiler barrel and was operated with only 250 psi or 17.2 bars. Its tasks were to evaporate the water and to feed the outside low-pressure cylinders, mixed with the exhaust steam of the high-pressure cylinder.

After it was completed in 1931 in the Angus Shops, Montreal, it was towed west and tested on the CPR's Mountain Subdivision. It was sometimes reported that drivers refused to operate this locomotive because they were frightened of the high pressure. In the result, it consumed 25 percent less fuel than comparable locomotives, but was much more complicated to maintain. Additionally, it spent many months in the shops for repairs. So like all very high pressure locomotives, it was not produced in series and withdrawn in 1936.