Stage one: water in
Everything starts with the feed. Distilled water in an inhalation system, or filtered and often reverse-osmosis water in a plumbed water appliance. Dissolved minerals are the enemy of a membrane stack; they deposit, they change conductivity, and they shorten service life.
Many consoles monitor water conductivity and warn when the feed is out of range. Those warnings are worth acting on immediately rather than dismissing.
Stage two: the stack
Inside the stack, cells are assembled in series to reach the required output. Direct current drives the split: oxygen and protons at the anode, hydrogen at the cathode, with the membrane conducting protons across.
Output scales with current and active area, which is why a 3000 mL/min platform is physically larger and thermally more demanding than a 900 mL/min unit rather than simply “turned up”.
Stage three: separation and venting
The oxygen produced at the anode is routed away and vented. This is the stage that mixed-gas designs skip, and skipping it is what produces an undifferentiated H₂/O₂ output.
Separation also simplifies everything downstream: only one gas has to be conditioned and metered.
Stage four: conditioning and delivery
Hydrogen leaving the stack is warm and saturated with water vapour. Moisture management, a humidifier bottle and appropriate tubing make a long session comfortable and keep condensate out of the wrong places.
Delivery then depends on modality: a nasal cannula for inhalation, a fine-bubble diffuser and circulation loop for bathing, or an in-line infusion point for drinking water.
What owners actually control
Three things: the water you put in, the run hours you ask for, and the cleaning schedule you keep. Those determine most of the difference between a stack that ages gracefully and one that does not.
Everything else — current regulation, thermal control, fault detection — is the machine's job, and is where engineering quality shows up over years rather than weeks.