Changing air source using Quick disconnect underwater

[Akimbo]

Sounds like that is the same way commercial divers use a pony bottle...

I have never seen that in commercial diving, or heard it suggested. Are you sure???

Commercial divers call them "bailout" bottles and have them hooked to a valve on the hat. It was common to see freeflow masks and hats (no demand regulator) before the 1980s, which didn't support bailouts. Take a look at the valve on the left side of the manifold on this hat:

SuperLite 27 | Kirby Morgan

The brass check valve on the back of the manifold is for the umbilical (surface or bell supply), which is a critical safety device to prevent hat squeeze in the event of an umbilical failure near the surface:


This check valve also prevents gas from the bailout escaping out the failed umbilical when the diver manually opens the valve. That valve connection at the back excepts a standard Scuba second stage hose. The forward facing "freeflow' valve is for ventilating the hat to reduce CO2 and defog the port.

Modern "lightweight" hats have a neck seal, similar to drysuits. The diver would get "squeezed" just like on the Myth Busters video if their neck dam is pointing down (without a check valve, freeflow open, and an umbilical failure near the surface). The hat would flood IF the freeflow valve was open at the time of the failure and the neck dam pointing up.

Edit: Regarding the original question: I would opt for a switch block on a Scuba-style FFM like the OTS, Ocean Reef, etc. Another option is to just put a regulator on your bailout with a second stage and carry a spare half-mask -- which is most commonly promoted in recreational FFM training.

Omni Swivel Gas Switch Block | Dive Right In Scuba - Plainfield, IL - Dive Right in Scuba

 

[Aanderson81]

It can be done, but should it...

I would connect the pony to the octo port on the FFM and dive with it closed. OOG? Open pony, breathe. Fiddling with a QD while out of gas? One fumble from disaster.

The gas block would definitely be the pro way to do it as Johnny suggests but they aren't cheap. You should already have the second stage adapter that came with the mask, so try the port first.

The ocean reef has a built in reg and a surface air valve. It doesn't have a second stage port.

 

[RainPilot]

My ocean reef has 2 ports, outside of the reg. one surface valve / octo and on the other side one for comms as seen below

If you've lost your adapter you can get one here

Ocean Reef Octopus Port Connector

When in use looks like this