VFT water level

[fredrosse]

I happen to be running a fancy Thermo-Hydraulic Computer program (GOTHIC) that makes quick work of this question.

Two identical small VFT boilers, about 24 inch diameter x 24 inch high, both filled with 358F Steam/Water, corresponding to 150 PSIA pressure. Boiler 1 has a water level 1 ft high, with 1 ft steam space above water level. Boiler 2 has a water level 1-1/2 ft high, with only 6 inches steam space above water level. No firing of either boiler, just constant steam output of 72 Pounds Per hour (typical launch steam flow) for each boiler.

The graphs below show how quickly steam pressure drops for each case, as the hot water flashes to continue supplying steam. Pressure reduces more quickly in the boiler that carries the lower initial water level. Both of them suffer a loss of level during the process.

[Lopez Mike]

I feel like I just got a message on a couple of stone tablets. It would take me all Winter to figure out how to run that program.

So the stored energy on the water is the trick. I guess it's a high glass this weekend.

The flip side of this issue for me is that when I do screw up and let the pressure drop way down, a low glass lets me get the pressure back up and get the heck out of the way of that ferry boat sooner. The smell of wood smoke is replaced at that moment by the odor of fear sweat.

Too busy tooting the whistle at babes in ski boats.

My neighbor just walked over. When I told him that we were expecting 27 boats at Blaine this weekend he said, "That will be a blast!"

Poor choice of words. Time for a quick hydro before I leave the yard.

[cyberbadger]

Mike,

Guess who wrote parts of the GOTHIC program? Fred Rosse (And he's not wrong)

barts is on the money. You may as well cut your boiler in half.

For a Vertical Fire Tube boiler, it's not very nice to the boiler life to run at low water level. (The fire-tubes don't like it, heating fatigue)

VFT's are not know for quick start up time. Maybe fill it up with an inch or two more then you typically have before.

You fill it too high and you will get carry over - (Water with the steam) and that's no good. Your engines won't like it, and any passengers or your self will not appreciate the scalding hot water.

Water in a boiler can expand up to 1700 times it's volume into steam. It's amazing. It's energy in the bank. Water tube boilers typically don't have that bank.
(Of course if you let the bank - a boiler - cool you loose the energy you have built up)

-CB

[Lopez Mike]

An interesting note is that I see very little change in the glass from cold to popping the safety. And yes, I've blown down the glass. With the hot well float system I have a small dirt line on the glass at the 'normal' level (soon to be raised!) so I have a good reference.

The glass level changes when the bow is pitched up or down on the trailer so I know it's indicating a correct level. Just no expansion with temperature changes. Maybe a VFT has so much water in it that there is less level change with heat. Dunno.

If it was all cut and dried it wouldn't be as interesting.

[Mike Rometer]

I would like to see what happens to the graph when the boiler is 7/8ths full.

[DetroiTug]

On the VFT exposed tube issue, it probably matters how hard it's fired, but there is definitely a significant amount of superheating going on. When I ran the test with low water ( I had some crummy green wood and I was trying everything to make steam), The steam temperature went high enough it burned the silkscreened lines off of the sight glass down to the water level. The lines looked like new to the top of the water level, above it black and peeled off. It came from Mcmaster carr and was a 425°F steam rated (easy view) sight glass. Only running about 50 psi. Needless to say, I've never ran it that low since.

-Ron

[cyberbadger]

An interesting note is that I see very little change in the glass from cold to popping the safety. And yes, I've blown down the glass. With the hot well float system I have a small dirt line on the glass at the 'normal' level (soon to be raised!) so I have a good reference.

That's not really that surprising. It's the whole up to 1700:1 expansion property.

I had my first dry bottom VFT (16" diam) once at Pop-Off pressure (125PSI for that boiler) - and I had an unfortunate situation occur.

This was on land in my drive way. One of the reasons I steamed up was to try a new steam siren I had bought from someone in England. It was a modern replica, and It looked great all brass, maybe had never seen steam before. It had it's own whistle valve included which looked great. This is were I made my mistake, I trusted the fancy looking whistle valve. At 125 PSI the whistle valve on it would NOT reseat. And I had not put in some kind of shut off valve between the siren and the boiler.

So I had to make a call. I didn't want to make angry neighbours with a steam siren that I couldn't stop. So I pulled the fire, and dumped all the steam to the atmosphere.


The sight glass only went down 1/4" or less from 125PSI down to ambient. All the steam I dumped which took minutes took a lot of the heat energy with it.

I learned my lesson. Don't trust a whistle valve, especially when you've never tried it before even if it looks fancy. I try to have at least two valves in series (ideally different types, or from different companies) from my boiler whenever practical/possible.

It's not very nice to a fire tube boiler to have this sudden of a thermal&pressure change, but I had to make a call. And I don't regret the call I made. It was a learning moment. Good thing I was on land. If I had been on the water things could have been a lot worse, and my call may have been different.

-CB

[Lopez Mike]

Whistle valves are a weird thing. I have one that just works. Never a wrong move. I have another that I've done everything to and it still acts up. I've recut the poppet valve on the lathe (the moving part). I've lapped and lapped. It's getting better but it's a pain and tiring. Lapping using the drill press doesn't gain me much at all. Just too fast I guess. I've got it down to a hiss on air. More grinding away when my arms recover a bit. Both are old Lunkenheimers.

I want a siren AND a calliope. Of course that will mean steaming by myself. Barbara has enough trouble with the one whistle I'm using now. The reason for the whistle valve drama is that I have a second whistle with a much lower sound level. Five notes too.

[fredrosse]

Thanks for the compliment about my having a part in the writing of the GOTHIC Computer code, however my computer programming work in these analytical areas ended in the mid-1980s. I had no hand in writing GOTHIC, but I have used this computer code in my work for almost two decades. My employer has the license to use it, and they must pay about $13,000 per year for the program. I have seen Westinghouse full page advertisements in trade magazines, the entire advert. stating that the Westinghouse Analysis Team knows how to use the GOTHIC program. A brief description of the GOTHIC program:

Electric Power Research Institute maintains the GOTHIC computer program, which can be used to simulate several power plant-related thermal – hydraulic transients. The GOTHIC program is widely used in the nuclear industry to model the effects of steam/water transients and their impact on various structures and equipment. The GOTHIC program is capable of modeling many physical conditions, including critical flow, multi-phase flow modeling, water accumulation and drainage, steam condensation and boiling, the heating of various structures or equipment, combustion, and various nuclear plant phenomenon, etc.

For myself, a steam engineer, it has lots of applications, although it is usually difficult to build complex models. Sometimes it is just easier to go out into the workshop and fire up the boiler, and run a test. Of course, that is much more difficult with a full size plant, when interrupting the machine interrupts a $700,000 USD per day revenue stream.

[cyberbadger]

Thanks for the compliment about my having a part in the writing of the GOTHIC Computer code, however my computer programming work in these analytical areas ended in the mid-1980s. I had no hand in writing GOTHIC, but I have used this computer code in my work for almost two decades.

Fred,

I misread your LinkedIn profile. Either way you have considerable industry high pressure steam experience.

-CB