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Post by Roger on Mar 1, 2019 11:33:35 GMT
I've started this separate thread from the one about Injector Design so we can keep that thread on topic. My requirements are that a boiler should be quick and easy to make and maintain, while being safe and controllable. Heating with anything other than Electricity necessarily complicates the design because heat transfer isn't as simple. My thoughts at this point are as follows... 1) Use something like this 1Kw Immersion Heater which is only 11" long and has a 2-1/4" thread. 2) Use thick walled Steel Pipe with one end blanked off and the other with a threaded piece to suit the immersion heater. 3) Use a 1Kw dimmer module to control the power. 4) Fit two safety valves and a water level gauge along the lines of those used in Locomotives. The boiler only needs to operate for a few minutes at a time, so keeping it small makes sense. Obviously it has to be big enough to provide enough steam. Any thoughts on this would be appreciated
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stevep
Elder Statesman
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Post by stevep on Mar 1, 2019 12:50:59 GMT
Will an immersion heater stand up to boiler pressure? A normal domestic water system will only have a couple of bar of pressure, whereas you will presumably want to go to about 6 bar (about 100 psi).
I don't expect that's something they include in the technical data.
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Post by RGR 60130 on Mar 1, 2019 13:01:50 GMT
My thoughts are aligned with Steve's regarding the factor of safety on the threads.
What pressure are you thinking of using Roger? 110 / 120 psi?
Reg
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uuu
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Post by uuu on Mar 1, 2019 13:21:00 GMT
DAG Brown describes a test valve, allowing you to test the delivery of an injector under back-pressure, but without the water filling up the boiler. The Pumphouse has one, and it's proved very useful when testing/comparing several injectors in sequence. You can also compare the amount of water delivered with the amount of feed water used, and derive the amount of steam consumed, and therefore the efficiency.
The test boiler used is vertical, probably designed for coal, but heated with a gas ring, hooked up to a propane bottle.
Wilf
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Post by andyhigham on Mar 1, 2019 14:03:57 GMT
An immersion heater will handle 100psi no problem. A good chunk of my work involves interfacing with industrial water heaters. They usually have a relief valve set at 7Bar to 10.5Bar to protect against over pressure from frozen pipes etc. I would fit an adjustable pressure switch to switch off the heater, something less to watch when playing with injectors. I would also fit a valve and hose leading outside to "dump" steam, otherwise you could end up with a boiler full to the brim when wishing to test an injector
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uuu
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Post by uuu on Mar 1, 2019 14:34:05 GMT
Would an immersion heater, if fitted as in a domestic hot water tank, complain if the upper part were in the steam space, rather than fully submerged?
Wilf
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Post by Roger on Mar 1, 2019 14:49:33 GMT
DAG Brown describes a test valve, allowing you to test the delivery of an injector under back-pressure, but without the water filling up the boiler. The Pumphouse has one, and it's proved very useful when testing/comparing several injectors in sequence. You can also compare the amount of water delivered with the amount of feed water used, and derive the amount of steam consumed, and therefore the efficiency. The test boiler used is vertical, probably designed for coal, but heated with a gas ring, hooked up to a propane bottle. Wilf Hi Wilf, There's a diagram of one in Bob Bramson's book too, that looks to be very useful. I'll certainly be making one of those.
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Post by Roger on Mar 1, 2019 14:52:58 GMT
Good points about the pressure suitability of Immersion heaters. From what Andy says, they seem robust enough, 100psi or so isn't that much on any seals really. The force on the thread is quite large, but the thread is massive so I can't see it being an issue. I'll do a hydraulic test anyway before going to steam.
That's a good idea about pressure control, that's probably worth doing.
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Post by David on Mar 1, 2019 23:08:23 GMT
We have tiny little threads in our boilers, like on the gauge glasses, etc. The dome is a pretty large area for the pressure to work against and is only held on by small screws. As for the opening for the element surely a flanged bronze fitting with suitable o-rings will work. Given your skill with CNC you could machine the flanges to match the inner and outer radii of the shell.
You could put one or more vertical stays in, with just nuts flanged at each end.
An electric pump driven by a level sensor to control the water level?
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Post by Roger on Mar 1, 2019 23:52:10 GMT
We have tiny little threads in our boilers, like on the gauge glasses, etc. The dome is a pretty large area for the pressure to work against and is only held on by small screws. As for the opening for the element surely a flanged bronze fitting with suitable o-rings will work. Given your skill with CNC you could machine the flanges to match the inner and outer radii of the shell. You could put one or more vertical stays in, with just nuts flanged at each end. An electric pump driven by a level sensor to control the water level? Hi David, The immersion heaters in the UK all have 2-1/4" BSP threads which are pretty coarse. If the end of the boiler is a thick steel plate, that thread could be cut directly into it. I've just sent a message to a local Steel Stockholder for a quote for some 6" diameter Seamless Steel pipe with 6mm wall thickness and long enough to take an 11" immersion heater. The current thought it to weld some 8mm plate on the inside at the ends and thread the end for the immersion heater so it's as close to the wall as possible. The idea is to rest it on its side. I'll see what they come back with. I want to keep it as simple as possible really. I'll use an injector and a manual pump for maintaining the level. I don't want to add any stays if I can help it, I'll just use thick materials instead.
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Post by David on Mar 2, 2019 0:07:24 GMT
I wasn't suggesting you needed stays. I assumed you'd use thick material for the ends with good threads or good-enough welding.
Because a heating element is in use to heat the water rather than heating the boiler shell itself to do the job there isn't the same worry about stainless breaking down over time with repeated high temp/cooling cycles we got so twisted up about down here a few years ago. Didn't seem to worry the US or Europeans and I don't think anyone died over there yet.
Your idea sounds good for a low effort way to get a testing boiler. Both ME and EIM have vertical boilers on the go at the moment with threaded stays and all sorts of carry-on that look way more work and expense than they're worth.
This could be a fun way to upset the purists... have an electric motor driving a generator to power the element and an electric water pump. Stick it on wheels. :)
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Post by steamer5 on Mar 2, 2019 7:46:43 GMT
Hi Rodger, I’m in catch up mode so finding an injector thread & a testing one is great!
One of the guys on the Model Makers forum published an article in Engineering in Miniature pre 2014, sorry havent got a year/date.....I’ll have to visit my Dad for a hunt or ask him to have a look thru his collection, for an electric boiler. He has put up some videos of it running his engines, he also included the control circuit with the PCB for its construction. I’ll get on to finding the article, maybe a day or 6!
Cheers Kerrin
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Post by doubletop on Mar 2, 2019 8:19:59 GMT
Roger
Someone has to say that whatever you do should attempt to meet the relevant boiler regs. Even if only for your own safety.
A 6" end plate at 100psi is going to be subject to 2,827lbs force and the 2.25" immersion mounting plate nearly 400lbs. That's without any safety factor applied.
Pete
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Post by Roger on Mar 2, 2019 8:44:26 GMT
I wasn't suggesting you needed stays. I assumed you'd use thick material for the ends with good threads or good-enough welding. Because a heating element is in use to heat the water rather than heating the boiler shell itself to do the job there isn't the same worry about stainless breaking down over time with repeated high temp/cooling cycles we got so twisted up about down here a few years ago. Didn't seem to worry the US or Europeans and I don't think anyone died over there yet. Your idea sounds good for a low effort way to get a testing boiler. Both ME and EIM have vertical boilers on the go at the moment with threaded stays and all sorts of carry-on that look way more work and expense than they're worth. This could be a fun way to upset the purists... have an electric motor driving a generator to power the element and an electric water pump. Stick it on wheels. I wouldn't completely rule out a stay near the middle, I'll see how it looks when I get that far. I was planning to use Steel tube rather than Stainless, purely because of cost. If it's really thick material and I take care of it, it will last for as long as I need it. This is not Model Engineering, it's just a means to an end. If you've got a boiler that can be pressed into service then that's fair enough, but I don't have anything suitable.
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Post by Roger on Mar 2, 2019 8:47:48 GMT
Roger Someone has to say that whatever you do should attempt to meet the relevant boiler regs. Even if only for your own safety. A 6" end plate at 100psi is going to be subject to 2,827lbs force and the 2.25" immersion mounting plate nearly 400lbs. That's without any safety factor applied. Pete Hi Pete, I share your concern, and that's why it will be tested as if it's an ME boiler. I won't be taking any unnecessary risks, it needs to be very solidly built.
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Post by Roger on Mar 2, 2019 8:55:38 GMT
Hi Rodger, I’m in catch up mode so finding an injector thread & a testing one is great! One of the guys on the Model Makers forum published an article in Engineering in Miniature pre 2014, sorry havent got a year/date.....I’ll have to visit my Dad for a hunt or ask him to have a look thru his collection, for an electric boiler. He has put up some videos of it running his engines, he also included the control circuit with the PCB for its construction. I’ll get on to finding the article, maybe a day or 6! Cheers Kerrin Hi Kerrin, I'm glad it's peeked your interest. Although an awful lot has been written over the years, from what I've seen so far, it's mostly repeating what's already out there, with a liberal helping of anecdotes. It's all interesting, so I'm curious to see if there's anything that hasn't already been said. I'm just surprised that there's been so little experimentation with things like End regulation and overflow valve arrangements. It seems like we've been stuck in a rut for 40 years. I suppose it's a bit intimidating, and the main reason people seem to get involved is because of the poor performance of commercial products. Scale appearance and experimenting with new ideas doesn't appear to be the driving force. Personally, I think there's a lot of room for experimentation for anyone interested in grappling with it. Much as I like Electronics and designing things, I aim to keep the test boiler crude and as simple as possible. I'll probably have some sort of feedback but I don't want it to turn into a major project, there's enough work in even a simple design.
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don9f
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Post by don9f on Mar 2, 2019 19:47:53 GMT
Roger Someone has to say that whatever you do should attempt to meet the relevant boiler regs. Even if only for your own safety. A 6" end plate at 100psi is going to be subject to 2,827lbs force and the 2.25" immersion mounting plate nearly 400lbs. That's without any safety factor applied. Pete Hi, just to clarify the thread, if it is a 2 1/4” BSP size, the actual major dia. of the thread is 2.587”, or 65.71mm. At 100psi, this equates to a force of around 525lbs. For anyone not familiar, BSP “sizes” relate to the nominal bore of the pipe, hence the apparent greater dia. of the thread. I know Roger will build it strong! Cheers Don
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Post by steamer5 on Mar 3, 2019 4:51:22 GMT
Hi Rodger, My Dad is on the case to find the date of the article! I’ll post up the date for anybody interested.
While talking to Dad he reminded me that one of the guys had built an electric boiler. So I rang him & had a chat. He built it to test safety valves he was making at the time, in this part of the world boiler pressures are typically 100 psi. So his boiler was about 150 to 175 mm dia by approx 400 to 500 long, he thinks it was 6mm wall with he thinks 5mm end plates with no stays....I was a little surprised at that. Fitted with a 1 kw element, he suggest go for a 1.5 kw one. He said to make sure when the element is installed that it’s horizontal so it’s as low as possible in the boiler to give max water level above. It has its own pressure gauge & safety(s), plus 2 steam takeoffs with isolation valves to fit remove & adjust the safety’s without depressurization the boiler etc. water gauge & drain valve, steam point for a pressure switch. He said he filled it thru the drain & vented via 1 of the isolation valves. He insulted the barrel but not the ends. I asked about a water pump but didn’t get an answer.....I borrowed the boiler to check my safety’s but can’t remember if one was fitted, guess with injector testing you will have that covered! He no longer owns the boiler but is happy to answer any questions, I know were the boiler is & could ring a friend there to help out if that is of any help.
Cheers Kerrin
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Post by Roger on Mar 3, 2019 7:56:44 GMT
Hi Rodger, My Dad is on the case to find the date of the article! I’ll post up the date for anybody interested. While talking to Dad he reminded me that one of the guys had built an electric boiler. So I rang him & had a chat. He built it to test safety valves he was making at the time, in this part of the world boiler pressures are typically 100 psi. So his boiler was about 150 to 175 mm dia by approx 400 to 500 long, he thinks it was 6mm wall with he thinks 5mm end plates with no stays....I was a little surprised at that. Fitted with a 1 kw element, he suggest go for a 1.5 kw one. He said to make sure when the element is installed that it’s horizontal so it’s as low as possible in the boiler to give max water level above. It has its own pressure gauge & safety(s), plus 2 steam takeoffs with isolation valves to fit remove & adjust the safety’s without depressurization the boiler etc. water gauge & drain valve, steam point for a pressure switch. He said he filled it thru the drain & vented via 1 of the isolation valves. He insulted the barrel but not the ends. I asked about a water pump but didn’t get an answer.....I borrowed the boiler to check my safety’s but can’t remember if one was fitted, guess with injector testing you will have that covered! He no longer owns the boiler but is happy to answer any questions, I know were the boiler is & could ring a friend there to help out if that is of any help. Cheers Kerrin Hi Kerrin, That's very interesting and is very much along the lines of what I'm proposing, although I think the diameter is a bit on the small size if you're trying to keep the element below the water line. That's why I was thinking of 6" pipe rather than 4". Do you know if it used a standard immersion heater? I can get one that's 3Kw in the size I can fit. I like the idea of a pressure switch, I'll have to look into that.
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Post by steamer5 on Mar 3, 2019 8:21:25 GMT
Hi Rodger, Um the pipe is either 6” or 7”.......he’s not sure were he got it from....7” is an odd ball size except in the oil & gas industry were they use some very strange sizes!
Yep the heater is a standard house hold element, would think 3 kw would be more than enuff! Yep a pressure switch would be a great addition, tweak the switch so that it cuts out say 5 psi below the safety lift point, means one less thing to remember to keep an eye on! The other option could be use 2 elements, you would need a controller, were you could have it switch both on / off or just one to help controll the steam generation, maybe of 2 different wattages.
Cheers Kerrin
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