During the years, Swiss AF used the Type MS22001 oxygen mask, according to its use, in different configurations: 

- As diluter demand mask, fitted with an additional inlet valve compatible with the economiser oxygen system installed on De Havilland  DH-100/ 115 and  Farner Werke (F+W) C-3605

- As pressure demand as used on DH-112, Hawker Hunter and GAMD Mirage III:  

- With different kind of suspensions and connectors, as the ubiquous MC-3 /3A and the less common AMP suitable for Mirage III:  

- Configured for specific aircraft oxygen configuration as for the DH-115 Vampire Trainer:  

- For Pilatus P.2, PC-6 and F+W C-3605 -  the "Röhrli" version):  

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Masks fitted with a magnetic (electret) microphone were identified by a blue adhesive tape glued to the connector with the inscription "M-MIK"; those with a carbon microphone tagged with a yellow label "C-MIK" bonded to the cable.

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- Configured for a  specific helmet, as for the Gueneau 316:  

The MS22001 had a long service life, below a 1980's issue with the new model of supplemental inlet valve and J-bayo.  

Right - The modified L/H oxygen mask bayonet. The end rivet is drilled out, a threaded insert is applied, and a locking pin is installed. The pin goes into the (also modified) helmet's bayonet receiver and is locked in position by a spring loaded bracket.

To unlock the bayonet the bracket must be pushed outwards.

 

The inlet or breathing-in valve was fitted on Swiss AF A-14H-Type and MS-22001 oxygen masks used on Pilatus P.2 and PC-6, F+W

C-3605, DH-100 and DH-115.

 
Installed on the cheek of the mask, the purpose of the valve is to accurately supply the requisite amount of ambient air to the oxygen breathed in from the economiser, in order to obtain maximum efficiency at all altitudes.

  

There are also opinions in which a subsidiary function of the inlet valve is to let in extra ambient air if the supply from the oxygen hose does not meet the demand by the user i.e. if the pilot is trying to breathe harder than the oxygen system can support.

For a description of the MS22001 mask please click HERE