Im working on a project where i want to control my waste oil heater with an arduino.
The main controls will stil be manual overrideable.
But i want things like blowers that spread the heat and that can make the heater put out more power to be controlled by the arduino.
That part is pretty easy, just using a few temperature sensors will get me the data i want and i have a relay board that can switch the fans on, no problem.
But now comes the part where i want it to control the flow through a heat exchanger too.
The heat exchanger is on a secondary flue that i want to have some kind of valve in. That valve controls the amount of hot gasses to pass through the heat exchanger.
But now comes the part where i was hoping some of you might be able to help out.
I can make the mechanical valve, thats the easy part.
But i want a failsafe valve since i want no chance at all of boiling that water.
That means i want the valve to have a spring return but still be controlled by electronics.
My first tought was using some kind of servo.
But will that work?
The thing where i want the spring return for is if there is a power outtage and my arduino stops working it wont detect that the water in the exhanger is getting hot, and the pump also wont work.
That means there i a risk of making steam.
So if you guys have an idea how i could open a spring loaded butterfly valve with an arduino it would be really nice.
O and i might have forgotten to tell this, but i dont want to spend 300$+ on an industrial valve that has everything i want, i dont have that kind of money for this project.
Hi,
Im working on a project where i want to control my waste oil heater with an arduino.
The main controls will stil be manual overrideable.
But i want things like blowers that spread the heat and that can make the heater put out more power to be controlled by the arduino.
That part is pretty easy, just using a few temperature sensors will get me the data i want and i have a relay board that can switch the fans on, no problem.
But now comes the part where i want it to control the flow through a heat exchanger too.
The heat exchanger is on a secondary flue that i want to have some kind of valve in. That valve controls the amount of hot gasses to pass through the heat exchanger.
But now comes the part where i was hoping some of you might be able to help out.
I can make the mechanical valve, thats the easy part.
But i want a failsafe valve since i want no chance at all of boiling that water.
That means i want the valve to have a spring return but still be controlled by electronics.
My first tought was using some kind of servo.
But will that work?
The thing where i want the spring return for is if there is a power outtage and my arduino stops working it wont detect that the water in the exhanger is getting hot, and the pump also wont work.
That means there i a risk of making steam.
So if you guys have an idea how i could open a spring loaded butterfly valve with an arduino it would be really nice.
O and i might have forgotten to tell this, but i dont want to spend 300$+ on an industrial valve that has everything i want, i dont have that kind of money for this project.
Sorry but point mode and spread will make it easier to read and get more forum members to read it.
Tom..... 
Thank you. I tought i put in the spaces in between, but sometimes thay disapear when i post. Strange things happen in my browser sometimes.
But i put your version in the main post now thank you for the help with that allready.
the solution could be as simple as a pressure temperature relief valve used on all hot water heaters as far as a solenoid valve you use a normally closed with power to open no power no flow
Yes but there are no normal solenoid valves that work with 0 pressure difference in 3 inch. I dont want to close the waterline, i want to close the pipe that brings the heat to the exchanger.
Closing the water line would be easy, a water accepting solenoid in 3/4" is available for as little as 10$. But a 3inch zero pressure difference valve starts at 300$ and they probably dont like flue kind of temeratures. That would probably add another 100$ to the price.
And a pressure/temperature relief wont be used as it will be open vented. But that still makes steam a dangerous thing. If it builds pressure to fast inside the heat exchanger it might break and spray water inside my oil burning furnace. The results wil probably be pretty bad, but im not even wanting to find out.
Can you draw a picture of your system? I do this sort of thing for a living but am having a hard time understanding what you are trying to control and how and if it's even a good idea - Not boiling water sounds like a good start, but taking too much heat from the exhaust can also cause problems with corrosion when the gases begin to condense. It's an air heater but you're adding a water heater? How far away is this "secondary flue?" What does the water heat exchanger look like? Is there a water pump for that or natural circulation? Is there a big external reservoir? Where does the heat go?what are you using it for? What type of heat exchanger? Tubular? Coil? A big pot? Are you saying the Flue pipe is a 3inch sheet metal?
What about a car thermostat - you can get various temperatures...
regards
Allan
I have added a very bad mobile drawing. But the burner tank and normal flue is a working system allready. I want to add the heat exchanger wich is an ulumium block like what you find in a central heating system. The reservoir wil be 10L first and might be made up to 60L if needed.
The point is to get hot water to the radiators at the far end of the building.
The second flue will be 3inch 2mm wall mild steel or stainless and the whole thing is used in a well ventilated space so not really scared of possible fumes going in the shed.
And what needs control is the valve from the big tank in to the pipe that go's trough the heat exchanger. That way it could quickly shut off 90+% of the heat if the water is going to hot. That is needed because the burner takes about 15min to die from the moment its turned off. And 15minutes is very long if you are scared of boiling the water.
And in the event of a power outtage the valve should shut itself because the pump wont work either so chances of it boiling are bigger. It should have some natural flow, but i dont want to rely on that.
i got a better looking drawing, still not great, but this probably shows what im trying to do. So as you can see the heat exchanger is on a secondary flue that needs to be opend and closed according to water temprature, but also needs to be closed in a power outtage, and that is where the hard part starts i think. Else i could just use and electric motor and 2 limit switches that it would touch and then stop at it or use a servo motor to control it. But i dont think that wil work against a spring load that is constantly trying to close it. And if it wil hold it open then it probably wont let the spring close it when the power go's down. And this thing is going to be in the shed so welding is being done there too, and that sometimes trips the breaker.
OK..sounds like a fun project. In full disclosure: I say it sounds fun but it is probably illegal and certainly comes with some danger. Many (most?) people I work with would call it idiotic. I'd be triple-checking everything for safety and still be nervous I missed something and I've been extensively trained in combustion and boilers, etc. Still...this kind of homebrew project ALWAYS comes with unexpected results even when I do them. I don't recommend making these mods as a good idea, but if it were me and I was determined to (because that's how I am) Here are some thoughts...
Before we get to answering your question I'd like to throw out a couple of thoughts before I forget:
Depending on how it's piped, I don't know that the main flue needs to always be open - you can divert more gases to the heat exchanger and always send it back tot he main flue as the water temp is satisfied. That will likely require another "valve" as you are calling it, but would be more typical for waste heat recovery systems. Since we're on the subject, I am going to change your terminology in this from "valve" to "damper." In the matter of ducts for moving air and flue gases we in the industry call things that close and open and divert the flow "dampers." Finally - as time and money permit I urge you to go to a closed system. An open system sucks air into the water. Water in your heated water causes all manner of problems not the least of which is carbonic acid corrosion of the piping/metals. We go through great lengths to keep air out of our circulated water systems and use chemicals to counter the effects. You'll need a expansion tank and a relief valve or preferably two because I'm a huge fan of redundancy. Probably legally would also need some inspections and such but I'm no lawyer nor do I work for the city, so I'd probably never bother in my own garage but it would be the safe thing to do - you seem bright enough to know that boiling or even just heated water can be dangerous as heck.
OK, so what you are looking for is a powered open, spring return damper actuator. They sell them for heating systems with a damper attached although I see them less commonly nowadays either because we've gone to smaller flues and powered vents or because I've gone to the commercial world and less often into homes. Google for flue gas dampers and see what you find. I don't recall - they might pricey. If you are like me and like to hack and do things yourself, you might take a 3 inch damper (or a 6 inch and cut it down because they're easier to find) and stick it in your pipe and make your own actuator. Many ways to get creative since this is for personal use even though most people would panic and think you a madman - I respect you, sir. A few thoughts on DIY auto-closing flue gas damper:
First thought is to have it arranged to gravity closes the thing - either by using vertical pipes or a weighted lever. From there - you just have to nudge it open when the water temps fall. My first idea for connecting the linkage is to make the physical connection between servo and damper with an electromagnet. Now power and the damper automatically falls closed. (also useful because you can add an extra over-temperature and/or overpressure safety switch that cuts power to the electromagnet).
BTW Are the flue gases powered by a fan? That can make life easier because if you do anything that reduces flow you can soot up your heat exchanger real quick and waste oil is already dirty stuff. That will kill your heat recovery efforts by coating everything with a layer of insulating soot. A powered vent makes it easier to divert without restricting too much. Also if flue gas temps drop...I mentioned those gases condensing? Not only can that eat your flue pipes/primary heat exchanger (at least you aren't sleeping in the shed? Still, please put a CO detector in there. Worth $20) but it can eat your damper - I've seen them fall right off and then you can't control output. Something to consider - frequently inspect that damper.
It sounds like you need what i think is called a thermal damper.
Basically a mechanical device which uses expansion and contraction of a material to control the valve.
Old idea and very reliable.
Close but I wouldn't say exactly that - as you need it to respond to water temp not the flue gas temp. They do make electric ones that you can then make a control for or you can use a regular manual damper and homebrew your own actuator for it.
ElEscalador:
Close but I wouldn't say exactly that - as you need it to respond to water temp not the flue gas temp.
I thought they existed.
My Granny had an old coal back boiler for water heating.
2 Position pull handle, in one position the temp was regulated, second position (boost ?)steam was easy to get.
elescalador i like your idea about gravity closing the damper, i didnt think of that yet. And i was thinking about using an electro magnet on a servo too. But then i tought maybe its even possible to have an electromagnet just open it by itself, that way eleminating even more parts and making it less likely to fail.
And the flue gasses are sort of powerd by a fan, its much like a normal natural gas powerd heating in that point. Its force fed with air in the burner.
And if i can get a working system for the secondary flue i might make a second damper in the main flue to get more out of the water to air heat exchanger. But i first want to see what happens like this. If it is allready giving me enough power then i wont bother with closing the main flue. But if it needs to put more heat in the water faster then i might try it.
And for the closed system, it would be better probably, but i want to run it like this first because if it fails for some reason this is probably the safest way to do it. No valves that might not be working, no chances of it really building pressure, and no surprise hot shower, you can see it coming this way. And if the controls are working well and nothing crazy happens im going to try and put in 1 or 2 pressure/temprature safety valves and an expansion tank. But for the testing purposes this seems the safest way for me. And if it all fails ill just reweld the hole in the heater and throw all the other parts in the scrap bin. That is also the reason i dont want to spend big money on parts for a testing setup. If it was a proven thing then it might be worth investing the money, but if there is about 50% chance it will never really work then its to much of a gamble.
