I must admit i had my doubts it would actually work myself but i was delighted to have been proven wrong. The biggest challenge was warming them all up, again this is technically not a true compound as the engines were all uncoupled but it was interesting to observe the running speeds of all three and to experiment with the regulator to see how slow vs PSI all three would run.
I have to say both the Stuart & PMR will run on less that 5 PSI as both are extremely well made, which i think made a big difference given the low pressures involved.