Also worth mentioning is the redesigned casting for the crown of the piston (part no.15). On the previous casting the screw hole for the screw that secures part no.14 was drilled right through the crown of the piston casting. The screw was then held in place by a nut on the underside of the piston crown. There were two issues with this design.
The first is that any attempt to loosen the screw that holds part no.14 in place would loosen the nut on the underside holding this screw in place. The nut would then be free to turn. As this nut is almost impossible to get a spanner or wrench on without removing all three brass valves it was something of a nuisance.
Secondly if a thread sealant, like Loctite, was not used it was possible for steam to escape from the bottom chamber through the hole that had been drilled in the crown of the piston to accommodate the screw. The new design also means that part no.14 can now be easily replaced without the use of any kind of sealant under part no.14 to ensure a pressure tight seal. You simply unscrew the old part no.14 and screw on the new, with no concerns of whether steam might be making its way up through the crown of the piston.
Below is an image looking up under the crown of the piston on the Bacchi, showing just how difficult the small nut (obscured) is to access on the old casting design:
With the valves removed (apart from the stub of the last one!)
The new casting design has been thickened at the point the screw is fixed with the addition of a rib. The hole for the screw is now of a smaller diameter and is threaded. This hole no longer goes right through the crown of the piston.
As a result you can quickly and easily replace part no.14 if you manage to melt part 14 as a result of running the Bacchi without water in the upper chamber.
Secondly, there is no chance of any steam escaping as there is no longer a hole through the crown of the piston. Again, this just improves the reliability and longevity of the Bacchi.
Additional refinements include bores that are now round as a result of improved castings and the removal of burrs from part 24.
There is a simple test to check that your Bacchi is in good working condition; holding the piston and cylinder assembly on the underside in both hands, use both thumbs to push the piston upwards against the force of the spring. The movement of the piston should be free and smooth, with no binding or sticking at any point of travel.