[QUOTE=Emrobu;196280]My lecturer was telling us about what to do if the boiler level is found to be too high. The list goes like this:
Close feed v/v, secure fires, stop fans, close stop v/v, call the chief and bridge, blow through the gauge glasses, and use the blow down v/v to bring the level down to normal. Then he says, but if you’re writing the USCG exam, you must choose the surface blow down v/v, not the bottom one.
Why? No one seems to know. Any one here have the skinny on why the surface v/v is a better choice than the bottom v/v?[/QUOTE]
The question posed has to do with what to do, not why the situation occurred.
With regards using the Bottom Blow (when the boiler is operating); Its [B]only[/B] purpose is to remove sludge, scale, and sediment that collects in the bottom of the mud drum. Opening the bottom blow valve can disrupt the natural circulation of water within the boiler resulting in tube or component failure. It should be done strictly in accordance to the the manufacturer’s operating instructions. Generally the bottom blow (and water wall drain) valves are opened and closed in short bursts.
If you have a high water situation opening the surface blow piping will bring the water level down to a safe level but not low enough to be unsafe.
The only time the gauge glasses are blown down is to remove debris that may have accumulated to obscure the reading of the water level, to ensure the piping to the gauge glass is clear, or confirm the gauge glass is full/out of sight. When done care must be taken not to washout/damage the mica protecting the glass. It is done (again) in very short bursts. With that said it is not done to drain down the steam drum.