British Aircrew J-Type Oxygen Masks
Based on the facepiece of the H-Type oxygen mask, the J-Type was designed to be used for pressure breathing at high altitudes in conjunction with a pressure waistcoat. It was the first in a short series of "Pressure Breathing" masks to be used by the RAF
A manually adjustable exhalation valve (the Mk1 Pressure Expiratory Valve) provides back-pressure in the mask, whcih in turn provides back-presusre to maintain the pressure waistcoat at the same pressure as the oxygen mask. The expiratory valve has three settings by a knob on the front of the mask, which adjusts the force of the expiratory valve spring. The knob needs to be manually adjusted to match altitude levels. The entire pressure breathing system is dependant on this valve as it is solely responsible for setting and maintaining the pressure.
In the effort to better seal the mask to the wearers face, the J-Type also differed from the H-Type by the addition of a nose stiffening piece, the chamois liner is replaced with closed cell foam rubber, and the elastic harness is replaced with a more solid webbing harness.
RAF/RN AP Resources
AP1182E, Volume 1, Section 4, Chapter 2, Figure 1 (AL70, 1958)
Typical AEA of early presure breathing equipment including the J-Type oxygen mask. Note that this AEA includes an unusual light colour / white F-Type helmet.
AP1182E, Volume 1, Section 4, Chapter 2, Figure 2 (AL59, 1956)
This 1956 dated AP gives a great overview of the J-Type mask conencted to a pressure waistcoat via the connecting box, as part of the AEA.
AP1182E, Volume 1, Section 4, Chapter 2, Figure 4 (AL59, 1956)
This 1956 dated AP shows all components of the J-Type oxygen mask.
AP1182E, Volume 1, Section 4, Chapter 2, Figure 5 (AL59, 1956)
Cross-section drawing of the pressure breathing expiratory valve Mk1, probably the most significant part of the pressure breathing system.
