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Medium sized monotube boiler

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vederstein

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(Yeah, this thread is quite old)

My boiler is of monotube design. A couple of notes:

1. The water inlet should have a check valve to prevent any steam back flow.
2. You must have a pressure relief valve. Mine is set to 100 psi. Have a pressure gauge as well.
3. A monotube boiler doesn't hold much water, so you'll be adding water constantly. I suggest an automatic system. My boiler controls run off an Arduino.
4. You'll need some type of indicator of water level. I used a spark plug. The water has enough minerals in it such that when the water reaches the spark plug, the gap is closed.
5. As steam bubbles form, they'll push water out with it. Your steam will be interlaced with water drops. My boiler has this issue and I've never fully fixed it. I believe a superheater is important as well as a steam dome. If I ever get a bug up my butt to build another one, this will be a significant improvement.
6. NEVER LET A MONOTUBE BOILER GO DRY! The tubes will soften and possibly burst. I have experience with this. It's why my water controls are automatic now.
7. Feedwater pump must have run at a higher pressure than your boiler or no water will go in.
8. My boiler is propane fed and the burner is a turkey fryer burner. With my arduino controls, I control the water level and the fire. If the water is low, the fire goes to pilot light. If the pressure is in range, the fire goes to pilot light. The arduino also turns on the feedwater pump if the water is low.
9. Have a way to safely exhaust the boiler with a manual valve.
10. My boiler is only run once or twice a year for demonstrations, so mineral build up isn't really an issue. When I'm done, I do run water through the entire boiler for a few minutes to remove excess minerals that may have built up.

New a view videos:

1 - Using a spark plug as a level sensor.
2 - An early test of the boiler.
3 - The boiler almost as it is currently. Since then I moved a pressure switch from the steam side (top) to the bottom where the water is cooler and then I can use more reliable and simpler pressure switches. (I've posted this video here before).
4 - Dumb **** you can do with a small steam engine.

I guess that's it.

...Ved.




 

taterfarmer

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I'm using a hydraulic cylinder on a metal frame for a water injection pump. put together like a hydraulic jack with a pump handle. 3/4" pipe and check valves. should push around a cup and half. 1500psi no problem . I'm using steel tubing in my monotube boiler .
aiming for 500 + psi
 

Steamchick

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Hi Tater-man!
Is the 500psi the test pressure? - for 220psi Safety-valve lift? - or is it your planned NWP - for an Hydraulic test at around 1500psi test? (your pump limit). ASME design calcs for Hydraulic test pressure consider the stresses generated by the pressure at Normal Working Pressure against the UTS of the steel at a temperature relating to the temperature of the steam or superheat. In a monotube boiler, the UTS of the material in the hottest zone where the steam is being superheated can be significantly below that at "room temperature", so you will have to understand how hot the pipe will get at the hottest point... so you can determine a suitable "cold hydraulic test pressure". - Check ASME regualations for the rules.
Vedrestein.
I like the technicalities you explain.. but then I am amazed at the engines you are powering with wet steam at "low" pressure using such a large boiler. I have some similar sized engines that run (for demonstration) on an air supply using a small refrigerator compressor - at 10~15 psi. When steaming I always have superheaters in my boilers - if only to try and get dry steam to the engine - but for safety and good engineering ALWAYS use proper metal tubes for steam lines that are lagged to reduce heat losses and condensation. (I wind a double layer of thick string or wool around the pipe).
Plastic pipe is OK - within its designed pressure limit - for air-line.
But plastic is dramatically weakened by the temperature of steam and I would not want to be in the vicinity of a broken steam line lashing around and blowing very hot wet stuff everywhere! One quick blast on skin or in your eye could be painful - or blinding! - An accident in the making I think? Please don't show potentially dangerous stuff on your videos... someone else may get hurt as a result.
Also, I was taught (as a young boy) that you must always blow steam through the engine while turning slowly to warm it and minimise the condensed water, otherwise after a few seconds running you'll develop an hydraulic lock from the condensate in the engine - and possibly damage the engine? Your vertical engine seemed to be hydraulic-locking?
Sorry to sound a bit like your mother - but please adopt safe practices.
K2
 

Steamchick

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Taterfarmer.
You could try this for information which applies to coil steam generators just as much as to "tank" boilers... becuase steam at pressure is just a dangerous, however you configure the boiler to generate steam.
https://www.hse.gov.uk/pubns/indg436.pdf - see attached.

As you are in the US of A the Fedral rules will apply to you, not HSE, but they will be very similar, I think?
The ASME regulations actually apply to you, but my UK location doesn't seem to find those...
I have been trying to understand guidance notes from various sources: the best guidance I can find considers coil boilers to be the same as superheaters and economisers for the sake of Regulation, so state that the ASME BPVC Section 1 applies - (Boiler and Pressure vessel code) - for "Equipment" and "Piping".
I think this is based on the water containing part being the same as an economiser, and the steam containing part being the same as a superheater, but check it out and decide for yourself.
Take care.
K2
 

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Richard Hed

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You could try this for information which applies to coil steam generators just as much as to "tank" boilers... becuase steam at pressure is just a dangerous, however you configure the boiler to generate steam.
Yes, Steam at pressure is dangerous, however, the two basic configurations: water tube and fire tube, are quite different in their dangerousness. A fire tube heats an enclosed vessel filled with water, and when that water is heated to pressure it has all the mass of water behind it ready to expand when it can. If a break in the vessel occurs, you have a huge repository of heated liquid/steam mass ready to escape. If this steam escapes out a crack, it is bad, if it escapes by explosion, it is worse than disasterous. However, if a water tube system develops a crack or worse, it is far less dangerous, as it USUALLY only develops a crack and it is contained inside the fire vessel (enclosed, that is) and the mass of heated water/steam is far less than the fire tube type. This is why water tubes are used over fire tubes today. The coil tube, of course, is of the water tube variety but a special type that heats the water very quickly. Even so, it is contained in the heating enclosure and is most likely to develop pin hole type leaks. Good for automobiles.

I see most of the toy pressure vessels we make, those of us on this forum, are of the fire tube type. The vessels are usually very small, having less than a gallon of water and 30 psi or less--still enough to melt the skin off your face if the vessel explodes because of faulty work but small enough to probably not kill the whole block of people living in the area. Even so, we want our vessels to be "original models", that is, to be miniatures of something we are copying/modeling. As for myself, I would prefer to use water tube type regardless of keeping exact models.
 

Steamchick

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Thanks Richard. I understand your point. But all boilers that are correctly made to approved designs with certified materials and processes, and with the correct controls and trained operators and management, should be safe. I am in a Model Eng. Club that has 70 plus members. More than half run steam - either stationary models or locos on the track where we provide passenger rides to the public. I understand the club members have never had a catastrophic failure. In 25 years I only know of one incident where a boiler was difficult to keep in steam because the boiler had developed a leak. I think the boiler was over 40 years old. All the locos are 'tank' type, as are most of the stationary and road engine boilers. But all boilers are tested and certified as complying with regulations. So I am a bit suprised at any reluctance to use that type of boiler? Of course, there are operational differences with tank and mono-tube boilers. It just depends on "operational needs" for the steam, as to which is most suitable, in my humble onion.
Cheers!
K2
 

Richard Hed

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Thanks Richard. I understand your point. But all boilers that are correctly made to approved designs with certified materials and processes, and with the correct controls and trained operators and management, should be safe. I am in a Model Eng. Club that has 70 plus members. More than half run steam - either stationary models or locos on the track where we provide passenger rides to the public. I understand the club members have never had a catastrophic failure. In 25 years I only know of one incident where a boiler was difficult to keep in steam because the boiler had developed a leak. I think the boiler was over 40 years old. All the locos are 'tank' type, as are most of the stationary and road engine boilers. But all boilers are tested and certified as complying with regulations. So I am a bit suprised at any reluctance to use that type of boiler? Of course, there are operational differences with tank and mono-tube boilers. It just depends on "operational needs" for the steam, as to which is most suitable, in my humble onion.
Cheers!
K2
Of course they are safe when built and operated correctly, I just thimk the water tube type are all round better and safer. I don't care about model exactness. I thimk there was a boiler explosion on a ship in Portland, Oregon harbor in the late 1890's--not sure if it was Oregon or some where else, not sure about the date, but apparently the explosion took out a block sized space, kilt many people.
 

Steamchick

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Fair comment on Victorian history, without real quality control of materials design and manufacture, never mind training of operators, and management of boiler rooms, boiler maintenance, etc.
I remember the 1960s when there was a traction engine (old then) and the stoker tapped the safety valve with a bit of metal... to let off some pressure. My Dad said it should work without being tapped! It was at some sort of fun fair (can't remember). But he led us away, and we couldn't stay and watch it. Funny how memories come back?
K2
 

Richard Hed

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Fair comment on Victorian history, without real quality control of materials design and manufacture, never mind training of operators, and management of boiler rooms, boiler maintenance, etc.
I remember the 1960s when there was a traction engine (old then) and the stoker tapped the safety valve with a bit of metal... to let off some pressure. My Dad said it should work without being tapped! It was at some sort of fun fair (can't remember). But he led us away, and we couldn't stay and watch it. Funny how memories come back?
K2
Well, tht reminds me, (I wasn't there in Portland when that ship blew), In 1913 when Stravinsky in Paris on opening night with The Rite of Spring, I had managed to get a perfect seat in gthe audience. soon after the music started, someone yelled "Booo", a couple minutes later someone else burst out laughing, then the boos started. Someone else yelled "Shut up, I want to see this", soon, a riot broke out. I crawled out of the theatre, thimking that I would return tomorrow. Well, the police were called to put down the riot in the theatre and the band played without missing a beat and the dancers not missing a step. The next day, I went early to get in line for tickets and it was a good thing I did. For in a few minutes the street was filled with persons trying to get tickets. Altogether 10,000 people showed up as the riot last night was reported in the papers and the public wanted in on the fun. I managed to get my ticket and get in the theater just in time to see the 10,000 start another riot. The police were called in again. So much for explosive situations, just a little music boiling a little too much.

Of course, this all pleased Stravinsky a great deal.
 

Steamchick

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Hi Richard, While I enjoy tall tales, if you were born in 1913 you would be 106 years old. Not unreal, just rare...
But for you to go "early to get in line for tickets " suggests you must have been at least 14... so that puts you about 122 years old? - So did you serve in the Great War? A couple of my teachers did.
Are you sure you are not simply recounting another's tale? - you look younger in your photo! And the tale reminds me of a tale my Grandfather told me - but I thought he said it was New York. But the records show you are right, it was Paris, so maybe he was just recounting a tale?
The riot at the Rite: the premiere of The Rite of Spring
He had sailed on the RMS Titanic, but in 1913 was on the RMS Olympic doing the New York run... having transferred from Titanic's working-up trials off Belfast, just a couple of weeks before Titanic sailed her maiden voyage, as his oppo on the Olympic went sick. He wrote in his journal how sick he was to miss the first trip on Titanic! - How lucky I am that he didn't! He was "4th Eng'r." running the Dynamos... - And that's NOT a tall tale.
While he did sail on many ships that foundered, I am sure he never experienced a boiler explosion! But his Father was the Lloyds Boiler Inspector for all the boilers manufactured in Sunderland, so maybe that influenced him to safe practices?
Our history is written, but we must write our future.
K2.
 

Richard Hed

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Hi Richard, While I enjoy tall tales, if you were born in 1913 you would be 106 years old. Not unreal, just rare...
But for you to go "early to get in line for tickets " suggests you must have been at least 14... so that puts you about 122 years old? - So did you serve in the Great War? A couple of my teachers did.
Are you sure you are not simply recounting another's tale? - you look younger in your photo! And the tale reminds me of a tale my Grandfather told me - but I thought he said it was New York. But the records show you are right, it was Paris, so maybe he was just recounting a tale?
The riot at the Rite: the premiere of The Rite of Spring
He had sailed on the RMS Titanic, but in 1913 was on the RMS Olympic doing the New York run... having transferred from Titanic's working-up trials off Belfast, just a couple of weeks before Titanic sailed her maiden voyage, as his oppo on the Olympic went sick. He wrote in his journal how sick he was to miss the first trip on Titanic! - How lucky I am that he didn't! He was "4th Eng'r." running the Dynamos... - And that's NOT a tall tale.
While he did sail on many ships that foundered, I am sure he never experienced a boiler explosion! But his Father was the Lloyds Boiler Inspector for all the boilers manufactured in Sunderland, so maybe that influenced him to safe practices?
Our history is written, but we must write our future.
K2.
Well, I was just a little tyke when I got to see the battle of Shiloh from a hilltop. I remember it well.
 

Steamchick

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Hi Richard,
And there was I hoping I was really talking to Methusalah's brother! You would be older than Goldstar!
If only our genetic heritage could capture memories from our ancestors... - but even then we could only inherit memories of youth and love. None of the memories of ageing and off-spring growing-up, work, adult stuff and retirement.... So maybe that is not such a bad thing?
But some of my favourite memories are things told me by people older than my parents, when I was a child. That folklaw has more veracity than "modern politics and the press"! - But that is another topic!
Cheers mate!
K2
 

goldstar31

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Of course, this all pleased Stravinsky a great deal.


And here was me enjoying Shakespeare's Midsummer Night's dream in the middle of yet another pandemic.
But for those who want to grasp anything about the Rite of Spring, might I suggest that you witness a variation on it from Walt Disney's Fantasia.
Of course if you think about the Spring of1913 anf then Spring 1914, you are looking at the death of the Archduke Ferdinand-and we know what happened- or do we?

Well history does repeat itself? So Richard - your story please
 

Richard Hed

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And here was me enjoying Shakespeare's Midsummer Night's dream in the middle of yet another pandemic.
But for those who want to grasp anything about the Rite of Spring, might I suggest that you witness a variation on it from Walt Disney's Fantasia.
Of course if you think about the Spring of1913 anf then Spring 1914, you are looking at the death of the Archduke Ferdinand-and we know what happened- or do we?

Well history does repeat itself? So Richard - your story please
Of course, just for you. So I went several times to the Rite and got used to that supremely strange music and was enjoying Paree when the Archduke was killt. We all thot it would blow over, but later we found that certain international banksters WANTED war--$$$$. I didn't want to join up when the war came, but I had to defend gay old Paree so I did join up. It just so happened that the unit I was in had a captain that I had known on the outside. He hated me ferociously, for why, I never knew, probably because of my humility and good looks and smarts too, of which he was most likely jealous.

I saw him first so fastidiously hid from him but eventually he spotted me in his company and I was partially undone. After that, I was put into the dirtiest and most dangerous positions he could put me. Oddly, he was poorly liked by all and one day in the feild when he had given us a particularly odious order of passing over an open field which the huns had their new water cooled machine guns trained on, an order which we could easily have avoided those guns by going thru the trees which surrounded the field, an order which was both incompetent and suicidal to perform . . . well somebody fragged the bastud--and it wasn't me but truthfully, I was relieved at that. A leuitenant took over and we went thru the trees, taking a couple casualties. We were turned back because of the machine guns but the next day . . .
 

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