Post by antique diver on Nov 9, 2023 15:32:31 GMT -8
This is the original appearance of the first stage pressure sensor in the original two stage Bendix Oxygen diluter unit (circa 1942). Changes in ambient pressure adjusts the clearance between the small 0.067" HP inlet orifice and the tapered end of the HP seat via the lever. As flying altitude increases the HP seat retracts from the orifice to send more Oxygen percentage to the aviator.
Unfortunately, diving with the Bendix "diving lung" makes this mechanism work in an opposite manner than designed, as it gradually reduces the seat to orifice clearance as diver descends. So it took a lot of adjusting and tinkering to get this system breathing ok below 15-20'.
We had been diving it with 1800 psi tanks, which seemed to work ok, but the life of the HP seat tip was taking a beating and needed removal for refinishing way too often. Three years later I found out that the Bendix was originally designed to work off a supply pressure of no more than 500 psi. The HP seat just wasn't up to that, so I added an in-line reg to drop the tank pressure to about 450, and leaving the original first and second stages intact while keeping the unit operating within its design parameters.
Apparently the abuse of diving for a few years with the 1800 psi had been hard on the bellows (as predicted by Phil!), and it finally gave up during a dive. It wasted some air and ascent was required.
Photo of the failed bellows shows how it blew apart. Phil was right about metal fatigue! Likely due to all the dives made with 4x the rated pressure input.
Well that was the start of a whole new approach to converting these beasts, and I have had much better luck with my recent two (and final) "diving lungs".
Unfortunately, diving with the Bendix "diving lung" makes this mechanism work in an opposite manner than designed, as it gradually reduces the seat to orifice clearance as diver descends. So it took a lot of adjusting and tinkering to get this system breathing ok below 15-20'.
We had been diving it with 1800 psi tanks, which seemed to work ok, but the life of the HP seat tip was taking a beating and needed removal for refinishing way too often. Three years later I found out that the Bendix was originally designed to work off a supply pressure of no more than 500 psi. The HP seat just wasn't up to that, so I added an in-line reg to drop the tank pressure to about 450, and leaving the original first and second stages intact while keeping the unit operating within its design parameters.
Apparently the abuse of diving for a few years with the 1800 psi had been hard on the bellows (as predicted by Phil!), and it finally gave up during a dive. It wasted some air and ascent was required.
Photo of the failed bellows shows how it blew apart. Phil was right about metal fatigue! Likely due to all the dives made with 4x the rated pressure input.
Well that was the start of a whole new approach to converting these beasts, and I have had much better luck with my recent two (and final) "diving lungs".
