Cascade system

The cascade system is a way of refilling small compressed gas cylinders or air cylinders (e.g. for breathing sets) by decanting from big (often blowtorch-sized) cylinders.

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(To make this easy the neck of the cylinder of the Siebe Gorman Salvus rebreather had the same thread as a blowtorch oxygen cylinder, but the opposite gender, for direct decanting.)

The big cylinders are put into an order, say A B C etc.

The small cylinder to be filled is connected to big cylinder A, then the gas or air is allowed to flow into the small cylinder. This is repeated with B, then C, etc, until the small cylinder is as full as needed or as full as can be got.

The result is that A drains faster than B, which drains faster than C; A is used for the first bulk of the filling of the small cylinder, which is then topped up from B, then from C, which keep a higher pressure for longer.