Monotube Boiler Design – Radical Thinking

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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fredrosse
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Re: Monotube Boiler Design – Radical Thinking

Post by fredrosse » Thu Sep 28, 2017 2:18 pm

It is a relatively simple matter to arrange a reciprocating feedwater pump to have variable stroke which can be modulated while underway. This feature can allow a large range of pumped flow adjustment while the main driving engine is continuously operating. A constant stroke eccentric (or crank journal, crank pin) acts on a simple link with two journals, one at each end.

The eccentric (or crank) connecting rod small journal is connected to one end of the simple link, call this pin connection "A". The other end of the simple link is held in fixed position, call this fixed pin connection "B". The reciprocating pump connecting rod pin, usually driven directly from a crankpin, is instead connected to pin "A". Thus the driving eccentric (or crank) connecting rod, the pump piston's connecting rod, and the simple link journal are all connected with a pin at "A".

By changing the position of the "B" journal, variable pump stroke is obtained. If any would like to see a sketch of this arrangement please let me know.
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Re: Monotube Boiler Design – Radical Thinking

Post by DetroiTug » Thu Sep 28, 2017 2:47 pm

Same principle, but I seen one that was like a Stephenson link with one end driven by an eccentric off the crank and the other was linked to a bearing on the crank shaft - an idler. Then a clevis and block on the Stephenson link that drove the pump rod, variable control was attained by simply moving the link back and forth.

A needle valve on the pump bypass can work too, but not as controllable.

-Ron
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Lopez Mike
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Re: Monotube Boiler Design – Radical Thinking

Post by Lopez Mike » Thu Sep 28, 2017 8:39 pm

Ahh. I hate to break the news but these launches are always changing the load. Speeding up and slowing down and heading into a breeze. You name it.
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Re: Monotube Boiler Design – Radical Thinking

Post by DetroiTug » Thu Sep 28, 2017 9:16 pm

Mike,

Yep :lol: and that is why it's better to have it easily adjusted, because it needs lots of adjusting.

-Ron
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Re: Monotube Boiler Design – Radical Thinking

Post by Lopez Mike » Thu Sep 28, 2017 11:59 pm

All of that is why my power plant is so simple.

I find it fascinating to fiddle with boiler and engine stuff when it's all on the bench. Water getting a little low? Adjust the feed water bypass valve. But when I'm actually on the water, especially with naive passengers and other marine distractions like boats and thin water and what have you, every system that isn't clamoring for attention is a blessing.

Let's see. In some sort of priority, my tasks are:
Boiler mustn't blow up.
Passengers mustn't burn their fingers, get tangled up in the monkey motion or fall overboard.
Must avoid other boats, the bottom of the water and fixed hazards like buoys, docks and whatever fresh hell life serves up.
Way down the list are the little joys of fiddling with valve and levers.
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Re: Monotube Boiler Design – Radical Thinking

Post by fredrosse » Fri Sep 29, 2017 12:07 pm

"......seen one that was like a Stephenson link with one end driven by an eccentric off the crank and the other was linked to a bearing on the crank shaft - an idler."

That seems to arrive at the same result as what I had described here. I like the mechanism that has no sliding surfaces, just pin (journal) connections. The pinned arrangement is far easier to build, and is very similar to the Marshall-Bremme-Klug valve gear on my engine.

With my steamer, having a firetube boiler and gas firing, I have rarely fiddled with the feedwater flow. My boat is slow, so I am generally running flat-out, engine at full gear (85% cutoff), fuel gas at max pressure, main steam holding at 95% of safety valve setting. Running in this condition the boiler level falls about one inch in 3 hours, easy to makeup with the hand pump. If I link up to about 70% cutoff, the engine driven feed pump will pump slightly more water than steam generation, and the level climbs about 1 inch per hour.
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Re: Monotube Boiler Design – Radical Thinking

Post by barts » Fri Sep 29, 2017 5:09 pm

Lopez Mike wrote: Let's see. In some sort of priority, my tasks are:
Boiler mustn't blow up.
Passengers mustn't burn their fingers, get tangled up in the monkey motion or fall overboard.
Must avoid other boats, the bottom of the water and fixed hazards like buoys, docks and whatever fresh hell life serves up.
Way down the list are the little joys of fiddling with valve and levers.
This is why Rainbow is getting a float valve. With an on-off feed pump, I end up having to toggle the valve every
10 to 20 minutes (big Scotch boiler). W/ a float valve, I can probably just add water so often.... perhaps only
once or twice a day when I fix the HP packing gland :).

- Bart
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Bart Smaalders http://smaalders.net/barts Menlo Park, CA
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Re: Monotube Boiler Design – Radical Thinking

Post by DetroiTug » Fri Sep 29, 2017 6:44 pm

Yeah, that float in the hotwell works pretty nice.

I had an idea for a chamber with an iron float in it connected to steam on top and boiler water on the bottom whereby the float controlled the pump bypass valve then I found out that it had been patented about a hundred years ago. I think they still use a boiler water level control like that commercially, Fred?

May try one of those someday. The steampump on the center trycock works, but it uses steam and throws away boiler water. In a situation where an abundance of boiler is had it's not a big deal.

We sorta highjacked the water control on a monotube subject, sorry about that

-Ron
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Re: Monotube Boiler Design – Radical Thinking

Post by Lopez Mike » Sat Sep 30, 2017 2:10 am

Hijacks are us!

You might route the exhaust from that steam pump to your hot well. That is, once you decide to stop dumping all sorts of lake water in you boiler and add a condenser and a hot well. Dig, dig.
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Re: Monotube Boiler Design – Radical Thinking

Post by fredrosse » Sat Sep 30, 2017 2:04 pm

".......I had an idea for a chamber with an iron float in it connected to steam on top and boiler water on the bottom whereby the float controlled the pump bypass valve then I found out that it had been patented about a hundred years ago. I think they still use a boiler water level control like that commercially, Fred? "

I have not seen this setup in commercial nor industrial applications, but there are plenty of things I have not seen, only been around for a little over 70 years, and only been seriously involved with steam for 62 years.
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