Retarders

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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Kelly Anderson
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Retarders

Post by Kelly Anderson » Thu Jul 20, 2017 1:17 am

Do any one of you have any experience with using retarders in the tubes of your VFT? Do you consider them to be good, bad, of indifferent? The stack temperature on mine is generally too high and sometimes pegs the 800 degree F thermometer on natural draft.
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barts
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Re: Retarders

Post by barts » Thu Jul 20, 2017 2:44 am

These can help... but consider a substantial economizer and a float value in the hotwell, so you'd continuously feeding hot water into the boiler.

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dhic001
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Re: Retarders

Post by dhic001 » Thu Jul 20, 2017 8:05 am

The need for them very much depends on tube size. Zeltic's old boiler didn't need them (1 1/2 inch od tubes), the other boiler with 1 3/4 inch od tubes does. Of course if your tubes are very small, or very long, retarders will not be of any use, and will make things worse. I have never got around to trying them, but another friend of mine felt that on solid fuel firing, it was better to fit a solid plugged tube down the middle of the tubes, (thus forcing the gases in the straight line up the sides of the tube) as they increased the heat transfer, but restricted the draft less. If you feel you might benefit from them, making a set of retarders is quick and easy, but be prepared to clean your tubes more often.
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Re: Retarders

Post by DetroiTug » Thu Jul 20, 2017 1:53 pm

I call them "turbulators" but same thing. 800 degrees is very high flue temp, 300-400 is about right. Yes install them, they break up the laminar layers of heat flow (highest temperatures go up the middle and do nothing) and they definitely do help. As Daniel points out, be prepared to clean flues more often especially with no draft induction. We had a discussion about this a long time ago and the consensus was it was better to have then run from the bottom of the tube only up to the normal water level - then from there up to the top with just an 1/8" wire with a T welded on, so they hang in the tube. It prevents overheating the tube in the steam space. If I remember correctly, Fred just has coils of stainless steel wire (think very long and loosely wound coil spring) in his and reported that they did the job. Anything to break up the laminar flow.

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Re: Retarders

Post by Mike Cole » Thu Jul 20, 2017 3:10 pm

There has been a few reports in the Funnel over the years about retarders and the out come is always the same ' A useful thing to fit for most VFT boilers'
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Re: Retarders

Post by fredrosse » Thu Jul 20, 2017 7:56 pm

I ran experiments with a single firetube boiler, propane flame, generating steam at 212F. My setup (1-1/4 inch OD firetube, 0.095 wall, 18 inches long) was constructed to determine how much steam generation I could get on a single tube. A propane torch put a fire directly into the tube bottom. Without a retarder, over 1000F gas temperature out of the firetube. Then I made coils of 0.120 diameter stainless steel wire, wound on the lathe, about 1 inch outside diameter, with about one inch between coil turns. Fuel consumption was cut in half to generate the same amount of steam, and outlet flue gas temp dropped to 410F.

Firing Propane, fouling of the fireside surfaces is not an issue, but with wood or coal firing the turbulators can get in the way of cleaning operations. For solid fuel firing I would recommend the option of spinning the turbulators to clean off the tube surface, or a good steam "sootblower". Cleaning the turbulators will not help heat transfer, although if they get enough fouling that might impede gas flow.
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Re: Retarders

Post by cyberbadger » Fri Jul 21, 2017 12:24 am

I think tubulators are generally good. It's something I have considered. I wonder about cleaning/maintenance.

I just asked http://fuelefficiencyllc.com to give me a quote for my boiler.

They want $877 for 75 36" long tubulators for 1.25" ID tubes. Wowzers.

-CB
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Lopez Mike
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Re: Retarders

Post by Lopez Mike » Fri Jul 21, 2017 2:07 am

I have run my VFT30 with and without them. My tubes are 1" I.D. and about 18" long. The turbulators are twisted from 7/8" mild steel about two turns in 12" which is how long they are. I was told that they didn't need to reach all the way to the bottom tube sheet.

Pros: I did notice improved fuel consumption but no serious change in the maximum output.

Cons: They are a pain to clean off when I take them out at the end of the season for tube cleaning. I burn soft wood and only need to brush out the tubes once a season. I'm not about to take each of those silly looking things and scrub away at them with a wire brush.

For no reason that I can remember, I forgot to drop them in this year. I'll have to look around for them and give them another try. Maybe this time I'll make some sort of decision and if I decide to use them I'll need too make new ones out of S.S. or copper or something that doesn't rust all to hell.

To hang each one I bent up a hunk of wire in an 'L' shape. One end is hooked through a hole in the unit and the 90 degree bend keeps them from falling down into the fire. They tinkle in there when I trailer the boat. Wish they knocked off the soot.
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