Why not adopt a higher boiler pressure?

Stuart McIntosh from Australia commented: “Higher boiler pressure must mean a smaller (lighter) piston disc and less unbalanced mass and reduced hammer blow. Efficiency would also be increased.”

Chris Newman’s replied to say: “Higher boiler pressure would provide all sorts of benefits, not least being higher efficiency. And you’re right too that it would mean smaller cylinders, pistons and hammer blow.

Wardale chose to be conservative with his boiler pressure for two related reasons:

  1. He wanted the design of the 5AT to be based on tried and proven technology, and 2100 kPa (310 psi) was commonly used in the USA;
  2. He wanted to avoid frightening the safety/approvals authorities by increasing the pressure higher than what had been accepted practice in the industry. He felt that it will be hard enough to get the 5AT approved without adding to the difficulties by adding extra “risks” (as a higher boiler pressure would likely be perceived).

If we can ever get the 5AT off the drawing board and onto the rails, then for certain the next step will be the development of the design to boost its performance further.”