blow job

When the Air Gauge needles in either cockpit tell you your 52’s air tanks need a top up, with all that awesome pressure in your Scuba tank, it’s hard not to crank that knob right up and just take care of business, pronto.

(Maybe you’re channeling Burt Lancaster in ‘Run Silent, Run Deep” or blowing tanks on your private Varshavyanka Class fantasy sub. hiding just off the Indonesian coast...)​

Your Air pressure gauges see things differently.

They’d much rather you crack that valve gently and pretend like you were filling from a pump dispensing “T Stoff” Rocket fuel.  

E-E-Easy does it.

But why ? 

Because if you ever hop up on the wing to watch your air gauge needles during a ground fill, you will notice the Emergency Tank indicates a charge more quickly than the Main.

The lines at the fill port split at a tee with a larger diameter line ( shown going left in this picture) spanning the short distance to the emergency tank. As a result it fills more quickly that the main,  sending that right hand needle skyrocketing

OK, but so what ?

Well in 1849, Monsieur Eugène Bourdon knew exactly what. 

After Dad had passed away, Eugène’s thoughts inexorably started straying away from his humdrum job at an optical business toward scientific instruments and cool steam engine stuff.

Knowing what the pressure was inside that boiler was a matter of genuine concern, so Eugène Bourdon came up with the idea of a flattened, rolled tube which would deform
(within its elastic limit) as pressure filled it from inside. Some elegant gears measured the deflection to drive an indicating needle and...

Voilà!

If you ever pick up a welding torch, his invention is telling you how much Gas is left in the cylinders. If you have Safety Fire Extinguishers around your house, some little flattened, round tube is telling you what’s going on inside that Red Extinguisher.

You go, Eugene !! 

Nailed it.

But if we abuse a Bourdon tube and it’s delicate internal mechanisms, what then? 

Repeatedly slamming full Scuba tank pressure into your air system such that the PRV is audibly shuddering seconds later, (instead of cracking the valve open gently), can cause damage to the mechanism of your Yak 52 air gauges, resulting in a zero reading or a stuck needle.

These gauges are there to help you. 

They’ll tell you, as you’re downwind after takeoff, whether or not you’re making air. 

During pre-flight, they’ll show whether or not there’s enough air in the emergency tank should you need to blow the mains down, or whether you have enough in the Main Air tank, this morning, to even attempt an engine start.

When you think about them like that, they have as much to do with your upcoming flight as the fuel gauge.

So don’t shoot the messenger, (if you don’t like what you read on the Air gauge). These are delicate, sensitive instruments, worthy of your care & respect.

The best way to confirm both your gauges are reporting accurately is to vent the pneumatic system. Judiciously crack the B nut at both Air Tanks, (when they are removed for Hydro testing for example) - and if the gauges indicate zero in this condition, subsequently responding to rising pressure when the tanks are reconnected & refilled, then you are good to go.

Next time you’re standing next to the fill port with your air whip in hand, ready to twist that bayonet and blast those tiny air lines for all they’re worth, instead, just close your eyes and embrace the Buddha.

With your careful hand controlling the Scuba valve, the air is simply passing from one universe to another.

Ommmmmm

Total oneness.

The sound of happy Air Pressure Gauges at work.