Priming the Boiler...

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Dieseldame
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Priming the Boiler...

Postby Dieseldame » Sun Dec 23, 2007 10:01 am

So, can someone help me understand what "priming the boiler" is as referred to as being dangerous in the "guaranteed fail question"?? Sounds like it can happen when the water level in a boiler is above the steam cock.

Second, what exactly is the danger of adding water to a boiler when the level is below the water cock? Details....I need details!

:lol:

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JK
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Postby JK » Sun Dec 23, 2007 12:38 pm

Priming the boiler is overfilling it so that water is carried over with the steam. This will have disastrous consequences downstream such as Water hammer and recip engine damage.
Adding water to a boiler when the water level is below the cock ( I am talking Scotch Marine Boiler)can cause a collapse of your combustion chamber or furnace.
If the water level is below the cock, you have no idea how low the water level is and the combustion chamber crown will be exposed. Relatively low temperature water added the boiler will cause shock to the boiler internals.
If you collapse the combustion chamber, you kill a lot of people as the remaining boiler water will flash to steam upon hitting atmospheric pressure.

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Dieseldame
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Many thanks

Postby Dieseldame » Sun Dec 23, 2007 3:17 pm

Thanks JK..excellent answer, much appreciated.

DD

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ArkSeaJumper
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Postby ArkSeaJumper » Mon Dec 24, 2007 2:05 am

Ahh
The lumpy steam question.

There is a small trick when the steam level is below the gauge glass, you can blow the water side down, if you get water, then the level is JUST below the gauge, but still 'safe' to top the water level up.

Happy Christmes to all

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JK
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Postby JK » Mon Dec 24, 2007 2:09 am

I made the assumption that the question referred to the 3 test cocks on the back of the boiler.
This actually happened to me when I was a young watchkeeper. It scared the hell out of me, especially when I realized how long the previous watch had been firing the boiler in this condition.
Happy days

Mery Christmas to you as well. You'll be seeing the big elf about 4 hours earlier then here

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Dieseldame
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Blow me down

Postby Dieseldame » Mon Dec 24, 2007 7:52 am

Okay, so now I'm a little confused again. But lets see if I can get this. There may be a sight glass below the test cocks..so if the water is above that but below the test cocks we are okay. If it is below the sight glass blowing it down will tell you if there is still water. The question I now have is how I would know what the level of water is between seeing water in the gauge and having no water from blow down. I'm assuming that at some point between these two levels the combustion chamber crown becomes exposed....?

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Sébastien
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Postby Sébastien » Mon Dec 24, 2007 9:39 am

Some boilers have three cocks on the gauge glass and that's it, but some boilers have long lengths of pipe connecting the gauge glass cocks to the boiler. On small boilers these pipes will be directly connected to the boiler while on large boilers there will be an extra two cocks to isolate these lines. These pipes are usually not horizontal (to let air escape) and therefore extend far below and above the level of the sight glass. For example you may have a boiler with a sight glass two feet high with the connections on the boiler one foot above the upper cock and two feet below the lower cock. What ArkSeaJumper and JK are referring to is the condition where the water level is above the lower connection on the boiler but not yet visible in the sight glass. Boiler manufacturers nearly always place the lower connection above the top level of the furnace so that water can be added without fear of damage due to thermal shock.

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JK
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Postby JK » Mon Dec 24, 2007 2:03 pm

And some boilers have 3 test cocks located in the back besides the gauge glass.

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The Dieselduck
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Safety first

Postby The Dieselduck » Tue Dec 25, 2007 9:24 pm

Perhaps I can simplify things by saying that if you do not see the level in the glass you are in dangerous territory for the stated reasons above.

Thats my two cents.
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TxMarEng
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Good answer Martin!

Postby TxMarEng » Fri Jan 04, 2008 11:22 am

Either scenario high or low, high being particular on a propulsion boiler or one driving TG's or cargo pump turbines makes for a not so happy day for an injunear!

Remember ~ "keep the lights burning while your on watch and don't try to dazzle the Chief with any fancy footwork"

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carbob
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Priming the boiler..

Postby carbob » Wed Feb 27, 2008 5:50 pm

I can't believe that we are still being taught about and questioned about Scotch marine boilers in examinations. Are there any still in service?

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JK
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Postby JK » Wed Feb 27, 2008 8:08 pm

The question never specified Scotch marine, that was my example.


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