Most of the larger companies such as Landi Renzo, Lavato, BRC … are fabricators of reductors.
Each fabricator has its own recepy.
The role of the reductor is to control and reduce the pressure of the gas which is coming from the tank at 9-16 bars to working pressure of 0,9-2,5 bars.
A good reductor is the one which achieves constant pressure in different modes of engine work.
Best for this purpose are two-leveled reductors.
They are more expensive, but their advantage is obvious.
Famous fabricators are: Landi Renzo and Tartarini.