Hotwell Sizing

[JonRiley56]

Hi,

Can anyone offer me some guidance as to how to size a hotwell ? I am going to be running about 200 lbs an hour at full steam, which should equate to about 25 gallons.

Jon

[Lopez Mike]

By the time you make room for a float valve and at least two compartments for dealing with oil removal, I suspect it will be large enough. As suggested many places, have your float fore and aft so that the boat rolling doesn't make it act up.

Also make sure you can look in there to see what is going on. Very instructive.

Mike

[JonRiley56]

Hi Mike,

So are you suggesting that I should have an hours worth of water in the hotwell ? It seems like it will be a pretty large tank, particularly allowing for some free space for sloshing etc. It will also be a lot of weight with 200lbs of water in the hotwell.

Comments ?

jon

[Lopez Mike]

I don't think any of us carries that much water. Not in the hot well, anyway. What I meant was that by the time you made it functional, it would hold enough water to take care of normal variations in feedwater delivery.

You will, of course, carry some make up water to take care of tooting, safety valve, burner usage, whatever. But the hot well shouldn't be so large that it doesn't get hot. Usually it is as hot as you can let it be and not have your feedwater pumps start to create steam on the suction side and thus not work.

Others may have useful advice. A gallon or so is more like it. Bart? How big is yours? (hotwell, that is)

Mike

[barts]

The Otter's hotwell holds a couple of gallons, I think, but the normal level is about 2/3 full. There's room for the float and oil separation stuff, and otherwise it's just an open stainless tank I found somewhere. It really doesn't matter very much....

- Bart

[JonRiley56]

Hi Bart,

If I have 2 gallons in the hotwell I will be turning it over 12 or so times mer hour, or once every five minutes. Does that sound right ?
Also, did you say that you arent using a pump on the condensing system ? I assume you bring the condensate in to the top of the hotwell if that is the case so that you dont have to overcome the headpressure of the water in the hotwell.

jon

[barts]

I don't use a vacuum or condensate pump; the engine runs at 30% or so cut-off so a bit of back pressure is a small price to pay for added simplicity.

Whether I bring the condensate over the edge (which I do since it goes into the oil separation area) or up from the bottom, the head is the same.

- Bart

[dhic001]

Based on my experience, most hotwells are too small. I don't run an automatic feed regulator, and I prefer it that way as it allows me more flexibility in my operations, I feed when I want to, rather than when the auto system says it wants to feed. As a result of this, a larger hotwell is preferable. If building one new, I would size it so that the volume of water in the height of the gauge glass can be accomodated in the hotwell, plus a few percent more. This would mean that if I start with a full glass, and run down to a near empty glass, I wouldn't be loosing any water overflowing into the bilge. Likewise, if the boiler is half full, and the hotwell half full, I can run up to a full glass (ie almost empty hotwell) or run down to a nearly empty glass 9ie almost full hotwell). the few extra percent would allow some extra capacity to ensure that when the gauge glass is full, the feed pump will still have some water to suck in a rolling sea.

If you are worried about getting the volume of water hot enough, run your whistle line drain back into the bottom of the hotwell. fitted with a needle valve, and cracked open for awhile it will heat the hotwell quite well. if you are oil firing, the same trick run through a heating coil in the oil tank works too.

Daniel

[JonRiley56]

Hi Daniel,

That makes a lot of sense. Do you start out with an essentially empty hot well then ? I would assume so. Also, I am not celar on the idea of a "whistle drain valve", I was under the impression that all the steam vented through the whistle was lost to the atmosphere. Are you talking about steam that condenses in the whistle pipe after it has been blown ? I have been on a boat b4 where every time the whistle was blow it would spray water. Is that part of the same issue ?

jon

[Lopez Mike]

I'm interested in this idea of a whistle drain valve. Do you mean after the valve or before it? I hadn't thought of keeping the whistle and line hot with a small bypass line that drained back to the hot well. The fuel consumption would be well worth it if it reduced the showering and made the silly thing sound better from the beginning of a toot. It sounds like me answering the phone first thing in the morning.

As to whether to use a float in the hotwell, I've been in boats equipped both ways and although it isn't a big deal to manually regulate the boiler level, I found it much nicer to be able to get my head out of the power plant area and enjoy the boating more. And when the system is plumbed in the usual way, there is manual override available at any time. I used to dislike automatic transmissions too but I've gotten lazy in my dotage.

Mike