Pre-heating boiler water

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Emfinger
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Re: Pre-heating boiler water

Post by Emfinger » Tue Apr 06, 2021 12:11 pm

Thank you all for your help....now I'm not sure witch way to go....but thank you
Tom

michaellynn2
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Re: Pre-heating boiler water

Post by michaellynn2 » Tue Apr 06, 2021 3:49 pm

Tom, I chuckle at all the advice from each of us on this topic. Every one of us made good points to the subject of water Pre-heating. I had a good friend once tell me, "KISS"!! He meant, "KEEP IT SIMPLE STUPID". I did not listen to him though. When a new gadget came out for the live steamer, I was first in line. If you are not sure then "KISS" might be the way to go. I built a specific locomotive and it had lots of appliances on it. The more gadgets on my live steamer the better I like it. At the end of the day though, there is a lot of cleaning to be done. If you burn coal, keep that in mind.
michael george

Emfinger
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Re: Pre-heating boiler water

Post by Emfinger » Wed Apr 07, 2021 10:40 am

Thanks for the KISS system. I just need to know more about boiler shock.
Oil eater
Tom

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pat1027
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Re: Pre-heating boiler water

Post by pat1027 » Wed Apr 07, 2021 2:07 pm

At the end of the day there would be two reasons to heat the feed water. One because you want to. Two because you are on the edge of generating enough steam and a small increase in efficiency might help. Personally if you can generate enough steam I would not bother.

Thermal shock is a mechanical force with rapid changes in temperature causing differential expansion/contraction. If the feed enters where it mixes with the boiler water, I cannot see the small amount of water being added with each stroke of a pump being sufficient to shock the boiler structure. Mine goes in at near the smoke box end above the tube. The only boiler issue we had was corrosion on the firebox side sheets.

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Bill Shields
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Re: Pre-heating boiler water

Post by Bill Shields » Wed Apr 07, 2021 2:53 pm

I have also run into people that are firmly convinced that you should only hydrotest boilers with 'preheated (warmed)' water since it will shock the boiler if you put cold water into it for the hydro.

there is often a disconnect between theory and need for real world concern..which is where engineering training and experience come into play
Too many things going on to bother listing them.

michaellynn2
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Re: Pre-heating boiler water

Post by michaellynn2 » Wed Apr 07, 2021 4:08 pm

Thermal shock occurs when cold water enters a hot boiler. ... The difference in water temperature causes the rapid expansion and contraction of equipment inside the boiler, including its tubes, tube sheets, valves, fittings, and piping.

I wanted to build an engine that had no dummy appliances. The Southern Ps4 1401 had a feedwater heater. In building a working feedwater heater I got the benefit of reduced water shock to my boiler. The topic was introduced on whether to preheat or not and how to do it. That is a personal decision. My boiler was put into service in 1977 and is still going strong. I will let that speak for itself.
michael george

Emfinger
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Re: Pre-heating boiler water

Post by Emfinger » Wed Apr 07, 2021 6:21 pm

Thanks
Tom

Berkman
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Re: Pre-heating boiler water

Post by Berkman » Wed Apr 07, 2021 6:42 pm

You will not find a single outfit that hydro tests a fullsized locomotive with cold water... it will always at least be ambient temp or slightly warmed. FRA regs call for 1.25X operating PSI for annual

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Bill Shields
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Re: Pre-heating boiler water

Post by Bill Shields » Wed Apr 07, 2021 7:16 pm

Not disagreeing that it is a viable concern on a full size boiler.
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Berkman
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Re: Pre-heating boiler water

Post by Berkman » Wed Apr 07, 2021 7:40 pm

I wonder what the actual temp rise is in using 3 or 4 SS pre heater tubes around the inside diameter of the smokebox assuming a moderately slow pumping speed.

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Bill Shields
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Re: Pre-heating boiler water

Post by Bill Shields » Wed Apr 07, 2021 7:58 pm

SS is the worst thing you can use. Heat transfer is maybe 1/30th that of copper.

Number is easy to calculate as long as you know actual temperatures involved...which to avoid speculation will require thermocouples that can be monitored during running and idling conditions....that will also record wheel rpm.

You can probably get an adapter and a phone app to do it.

Once you know temperatures.. which will be highest during running load then you can calculate temp rise based on flow rate determined by rpm and pump displacement and an guesstimate on pump recycle.

Doable but more trouble than worth unless you are in inveterate tinkerer
Last edited by Bill Shields on Wed Apr 07, 2021 8:05 pm, edited 1 time in total.
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Berkman
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Re: Pre-heating boiler water

Post by Berkman » Wed Apr 07, 2021 8:04 pm

ya but it will last much longer with a coal burner.

After an hour or two of running and the SS will be up to the same temp as the smokebox anyway.

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