OP
designbysue
Contributor
Tanks will cool after filling and pressure is related to temperature? If there was a time lag between testing the tank when you picked it up and when you hooked up your computer, the tank will likely have cooled somewhat and the pressure will be lower. Unlike pressure gauges, O2 analyzers are easily calibrated. When the sensor is no longer working, the readings get weird. If the pressure gauge is off by a bit, no real harm besides potentially cutting off a few minutes of someone's dive. A faulty O2 analyzer, on the other hand, could lead to real problems and I doubt Buddy would risk that.
It turned out (Francesca told me late in the week) that the low tank pressure of the tanks on the boat is caused by the crew handling them. They grab them by the valves and inadvertently open them a small amount and don't check to make sure they are closed. This allows the air to escape - a little to a lot - one tank was at 1700#, another at 2000# and others at 2500#. There is a potential danger here if the diver doesn't check the pressure before diving (yes as they should and I have made a habit to - but it happens, especially to new divers). Also it was a nuisance to change tanks once you were set up. Sometimes we went through 3 tanks before we found a full one (after the first we would use our regulator to test the tanks before moving our gear over.) The tanks we tested on the dock were pretty consistently in the 2900 - 3000# range.
With regard to the nitrox mix, I tried 3 different analyzers on the boat - 2 of the one style would read 28% and the 1 of the other style ready 30% - and this happened on several tanks. This was mentioned to the staff on the boat but they didn't address the concern. The analyzer on the dock give readings of 28 - 29%.