Boiler install questions

[dhic001]

When lighting off a vertical fire tube boiler, the boiler should be totally filled with water before the fire is lighted. Once steam begins to form, the water should be "blown down" (here's where a surface blow down valve/connection is desireable) to the correct level. The area of the tube(s) above the water is now partially protected by steam. Your VFT boiler will last much longer is this rule is observed.

That idea is news to me, and I wonder how you intend to get your boiler completely full? I generally leave mine fairly full, but short of fitting a hand pump and pumping until it all comes out the safety valve, I can't see how you can do it. Its never been done with Zeltic's boiler, and there is no sign of any corrosion or damage at a certain part of the boiler.
Daniel

[froya66]

Hi

When I leave my VFT boiler, fire is out and a litle pressure is left, the vacuum formed when the boiler cools down will often fill the boiler to the top tube plate (and nearly empty the hot well)

When I start firing again, the pressure will rise very quickly, and I have to start blowing down to ensure that the water does not blow out through the safety valve.

I have often thought of installing a vacuum "snifting" valve in order to avoid this.

When I run the boiler puffing, I am sure that the temperature of the tubes above the water surface is quite high, but until now I have had no problems, so now where I see the argument from Artemis I do believe that even the minor steam cooling plays a role.

I think I will leave everything it as it is.

Regards
Jørgen

[Edward]

There seem to be almost as many different opinions as to how to put a boiler to bed for a short sleep as there are people who have thought about it .

This is what Roger Mallinson , who runs and until very recently owned SL SHAMROCK does :
1) A few hundred yards from the boathouse inject to put water into the boiler to a fairly high level , about 3/4 to 4/5 of a full glass.
2) Rake the fire down into the wet ashpan .
3) Steam the last few hundred yards to the boahouse .
4) Clean out ashpan .
His thinking is that by having a fullish boiler the volume above the water level is reduced , by running the engine for a few minutes after filling the boiler most or all of the free oxygen in the water will have been boiled off and exhausted through the engine .

I don't know whether he's right about this , but he has run SHAMROCK for about 35 years averaging at a guess 350 hours per year and is on his second set of tubes though he thinks he'll have to renew them soon .
SHAMROCK steams on Windermere which is a lake of good quality feed water , Roger also blows down frequently , usually about 1/3 of a glass once per outing . She has a side fired locomotive boiler with 32 x 1 1/4" tubes , more details at : http://www.steamboat.org.uk/register/html/sham0534.htm .
http://www.shamrocktrust.org.uk/


Regards Edward .

[dhic001]

Hi

When I leave my VFT boiler, fire is out and a litle pressure is left, the vacuum formed when the boiler cools down will often fill the boiler to the top tube plate (and nearly empty the hot well)

When I start firing again, the pressure will rise very quickly, and I have to start blowing down to ensure that the water does not blow out through the safety valve.

I have often thought of installing a vacuum "snifting" valve in order to avoid this.

When I run the boiler puffing, I am sure that the temperature of the tubes above the water surface is quite high, but until now I have had no problems, so now where I see the argument from Artemis I do believe that even the minor steam cooling plays a role.

I think I will leave everything it as it is.

Regards
Jørgen

Jorgen,
Have you thought about fitting a drain syatem so you can drain the excess water back to the hotwell, rather than blow it over the side? Particularly if you are using feed treatment, it seems a waste to dump that water. Zeltic will suck her tank dry too if you let it, but when I close down I always shut all the boiler valves, so preventing that from happening.

A few years ago Zeltic's former owner ran some tests on his former boat whith a number of heat probes. The boiler (a 3ft high vertical firetube type) ha probes inserted down the tubes, one to the bottom tubeplate level, on 1 foot up, another two feet up, and a final one in the smokebox. The test runs showed that no matter whether running at a low glass (water 1 foot above tubeplate) or high glass, the majority of the heat was pulled out in the first third of the tube, and very little change was noted therafter. As a result of this, the boiler designed for S.S. Kapanui a few years ago was very large in diameter, but very short in height. The whole boiler (minus the dry firebox) is about 2 feet high, but much larger in diamater and has many smallish tubes.

Daniel

[mcandrew1894]

You could fill it to half full to minimize the load and then use an injector once you got up steam...........just thinking out loud..

Dave

When lighting off a vertical fire tube boiler, the boiler should be totally filled with water before the fire is lighted. Once steam begins to form, the water should be "blown down" (here's where a surface blow down valve/connection is desireable) to the correct level. The area of the tube(s) above the water is now partially protected by steam. Your VFT boiler will last much longer is this rule is observed.

Yes Ron , that is the correct way to do it. However that wasn't the question.

However, if one was to fill the boiler half way, open the top trycock to bleed the air out and let steam fill the space above, brought the water to a boil, and perhaps no more, and then pulled the fire and closed the trycock, a good deal of the remainder of the boiler would be filled thanks to mother nature, as My boiler does while I am driving my boat home.

Leaving the boiler completely topped off is good practice as it helps to keep air out and your less likely to form a rust " groove" at the water line. This is how "Sabino" is put up every night...we top off with the injector until rejection, first drawing from the hot well, and when that's empty, from the feed tank.


However, can't you just ask an understanding local to use their garden hose?.....

Dave

[DetroiTug]

Thanks for the input on this...

The full when firing up is good to know and I understand the reasoning.

The reason I asked is because some of the rivers I plan on going to, like the AuSable up in Northern Michigan, the ramps are basically out in the middle of nowhere.. No hydrants readily available. I could probably stop at a gas station on the way..

I'll probably resort to some sort of small electric pump, maybe I'll make a portable one that uses a battery pack from an RC car. I'm really trying to keep from putting a 12 volt marine battery on this if I can. That's been sort of the plan all the way, heck, I even have oil burning bow and stern lights

I do have a 3" Navy manual bilge pump, I could probably use that.

-Ron

[mcandrew1894]

Oh yes how about one of those battery powered bilge pumps...should be cheap....

Dave

[froya66]

Jorgen,

Have you thought about fitting a drain syatem so you can drain the excess water back to the hotwell.....

A few years ago Zeltic's former owner ran some tests on his former boat whith a number of heat probes......

Daniel

Hi Daniel

I haven’t thought about the drain. Seems to be a good idea.

I have been afraid of damaging my fire tubes when I force the boiler hard, especially at low water level!

The temperature test you talk about sounds extremely interesting. If you could get the data from that test I would appreciate a copy.

Best regards
Jørgen

[dhic001]

I doubt the data is still around Jorgen, the tests were done in the late 80s, and if written down, would have been recorded in the boats log. The log may still exist, but I don't know where. I will ask when the chap gets back in the country, but i wouldn't hold much hope.
Daniel

[Edward]

Unfortunately most of my library is in storage so I can't look up the exact details and figures , but I fully support dhic001/Daniel in his claim that the tubes in a fire tube boiler contribute surprisingly little to the overall evaporative process .
Not having my books to hand I can't be precise but I think it was reported by a committee reporting to the British Admiralty in 1901 that in a locomotive boiler about 85% of evaporation came from the firebox and 15% from the tubes . Of the 15% coming from the tubes something like 80% came from the first 10% of the tube .
This committee had been first set up in 1893 and was known as the Boiler Committee ; it made numerous reports but I'm afraid that I can't remember in which report this information was included.
No doubt someone with a knowledge of history will correct my figures but I think they're about right .

Given this I'm slightly surprised that Daniel appears to favour a "dry" firebox for a vertical fire tube boiler rather than a "wet"/waterleg one,
(see paragraph 6. of his posting of 14th October concerning " Input on Boiler Design " in the "Technical-Engines and Boilers " section of this forum .) I think that all of the points he notes there are valid but given the greater exposure to radiant heat of the wet firebox I think he arrives at the wrong answer .

Regards Edward .