trevormc Senior Member Joined: 11 Jul 2013 Posts: 27 Location: Cape Town, South Africa Expertise: I love coffee
Posted Thu Feb 13, 2014, 11:02pm Subject: Steam boiler design
I am busy designing a dual boiler machine, and need some help with the steam boiler design. It will be an upright standing boiler
The pipe diameter is 100mm internal, and currently it's height is 200mm This makes 1.57L
My element is likely to be a spiral design about 100-120mm in height and about 90mm in diameter (will get it custom built to be 2Kw) - unless someone has some good advise for about that power? This leaves about 60-70mm for steam volume - 0.55L Is this enough to produce good long lasting steam pressure?
I will obviously use a pressure-stat and level sensor - Set to 1.2 bar I'm told..
I have not studied boiler design but I must wonder why you are going through this. If it is just because you enjoy it, that's fine, be my guest but if it is to try to get a dual boiler machine, for less than they sell for on the open market, it is very unlikely that is going to happen, custom designs esp when custom to this level, nearly always cost twice as much as you guess and take 3 times as long to make.
A scrap used commercial machine would be a great source for parts and has the advantage of having all the design work done for you, then again, you may find that the scrap used commercial machine requires a lot less work to be brought back to life than making a machine from scratch.
Like I said, if you just enjoy the process, go right ahead and knock yourself out!
In real life, my name is Wayne P. Anything I post is personal opinion and is only worth as much as anyone else's personal opinion. YMMV!
Feed the newbs, starve the trolls and above all enjoy what you drink!
Yip, it's because I can.. and I enjoy it. It gives my brain something to focus on and de-stress with..
I have a contact for used parts, and I will be using and modifying parts from my existing machines as well.
I'm mainly going to be building the boilers, and the casing. The electronics aren't a problem, and pipes + fittings are easily obtainable too.
Yea I know it'll work out more expensive in the long run, but living in the part of the world where I do, with an exchange rate of 10 to the dollar and 14 to the pound.. buying used machines isn't that affordable for me as it is for you guys - unless I find a rare bargain at some point. Also, it's easier on the wallet spending little amounts as they become available, than all in one go for a decent 2nd hand machine.
It's a long term project, so I'm not in a major rush to get it done.
Tonight I'm hoping to finish the wiring of the PID I bought for my Carezza, and that will do quite nicely until my new machine is ready.
Back to the original post's question. I have decided to reduce my brew boiler to 1.3L, and make my steam boiler a 2L. I'm limited by the length of stainless pipe I have..
Hi, Trevor, sounds like an interesting venture. May I suggest: you really should be consulting an engineer versed on thermodynamics for this. There are ratio's of volume of water to wattage output to look into, but there are many many other factors to take into consideration as well. However, why not use an already accepted and successful machines design specifications and use the same parts they have used as a starting point? Take, for a good example, the La Marzocco GS3. The steam boiler is 3.5 liters, and the 110 volt versions use a 500 watt element (the 200 and 220 volt versions use 800 watt elements).
That is interesting about the LM's boiler + element.. Trying to find an engineer to talk to about thermodynamics, is going to be interesting.. ;)
I'll certainly look into other machine designs as well... "The Brewtus III's 1.7 litre brew boiler is the largest in its classó which is also great for temperature stability. The greater the water mass, the less other factors affect the temperature. The boilers have a high-quality foil-faced foam insulation and each boiler is rated at 1250-watts (@125 V) with each boiler operating separately." - which is roughly in the same ball park as the LM So I'm not too far off with the brew boiler's potential design at the moment..
The steam boiler is the interesting one for me.. So I'll do some more research :)
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