Hot wells

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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Full Steam Ahead
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Boat Name: Frances Ann
Location: Cheshire, UK

Re: Hot wells

Post by PeteThePen1 » Wed Oct 07, 2020 10:39 am

Thanks Fred and Mike

It was useful to have that clear explanation. Would I be right in thinking that a good design point for a hot well would be to make it tall with a small surface area with the volume being less important. That should mean that the level will drop quite quickly as water is pumped into the boiler thus ensuring the proper action of the float valve. The small surface area would also be good for minimising oxygen absorption as was mentioned earlier.

As you can imagine I am still somewhat worried about the hot well installation recently fitted to Frances Ann. It is just a pity it was not possible to test it before she was laid up for the winter.


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Boat Name: Margaret S.
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Re: Hot wells

Post by fredrosse » Wed Oct 07, 2020 1:18 pm

A tall/low free surface area (air/water interface area) hotwell tank will amplify the level changes that occur in the boiler, and can therefore attain more reliable float actuated bypass valve action. Also the float valve action will be less susceptible to rocking and rolling of the boat in rough seas. However, "every stick has two ends"..........

Design considerations here will depend on the required range of hotwell level change to allow reliable float valve operation, as well as the boiler's sensitivity to level change vs. the boiler safe water mass. Obviously these parameters can vary widely, however many steamboaters have attained satisfactory operation with "typical" installations. Whatever "typical" means. I think Barts recommendations are close to what often works satisfactorily.

Of course you could have a float level/valve configuration that only needs a small hotwell level change for actuation, and that setup may be finicky in rough seas. A less sensitive float valve, requiring several inches hotwell level change for actuation may be causing troublesome boiler level transients, especially for a boiler that has a rather small acceptable mass change from high to low boiler level. In that case a tall/skinny hotwell may be in order. Some numbers need to be examined here to arrive at the proper solution.

Interesting that the last time I worked on these design considerations was in 1970, where the boat steam plant had to operate OK with a list of up to 30 degrees, as well as a 30 degree dive angle. Probably not so much of a problem with our steamboats.
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Lopez Mike
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Re: Hot wells

Post by Lopez Mike » Fri Oct 09, 2020 11:07 pm

My hot well is narrow and deep. Narrow from port to starboard, that is. Maybe 5 or six inches wide. I have no problem, with rolling in a seaway or boat wake. The float seems to ignore such things. And it controls the level to within a few millimeters.

I am most satisfied with my float valve which was meant to control the water level in a water tank for farm animals. Cheap and available anywhere there are cows and the like. No friction at all. I do find that it rattles sometimes when trailering with a low hot well. I cram a rag in there.

The level is so constant in both the well and the boiler that a scum line develops over time both in the hot well and the boiler water glass. It works perhaps too well as I sometimes get complacent and don't watch the glass closely enough.
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Re: Hot wells

Post by barts » Sat Oct 10, 2020 12:03 am

I made a new hot well a while back for Rainbow, but have had no chance to try it out as yet.... the float valve is actuated via a ball chain from the float to allow the use of a large float in a small space. The hot well is about 6"x7" inches or so, and about 20" tall iirc.
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Re: Hot wells

Post by ccdewitt » Sat Oct 10, 2020 4:33 am

This all good stuff. Thanks to all who responded tot the original question.
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