First off, playing with steam – especially under pressure is a dangerous thing. Failure to use common sense and a healthy dose of caution can melt the flesh from your bones.
However, if channeled properly steam can transmit a lot of power and turn heat to torque.
I have already shown you my weed-eater conversion to a basic single acting steam engine, now I will show my home workshop boiler. This portion of the project caused me the most sleepless nights and research, and I fully expect you to do your own research if you plan to create your own boiler. As I am not there to ensure you take the necessary precautions, I cannot be held liable for your actions.
That being said I used a pressure cooker for my boiler. I did this because I know it is tested to the pressures I plan on using for my boiler. I flirted briefly with a firetube boiler, but in the end, I feel much careful using something that was designed and constructed to boil water under pressure.
My pressure cooker (as well as every other cooker I have seen) has a pressure release that is designed to rupture well before the pressures inside the cooker endanger the integrity of the cooker itself. If this every goes off cut the heat immediately and get AWAY.
The pressure cooker has a pressure gauge on it also. The Agricultural extension office will test your gauge to ensure it is accurate (for food safety purposes) This calibration should be done annually, for food preservation and I would suggest you get it checked BEFORE you modify your boiler, as I doubt they will test it with a roll of copper pipe coming out the end. They may even call the revenuer’s thinking you have built a still… (By the way, my boiler is aluminum, and that reacts with alcohol so my steam boiler is in no shape, form, or fashion an alcohol distillation device.)
The other thing your pressure cooker should have on it is a weight of some kind to let steam out during the cooking process. This is the only thing of the three you should mess with. I used some tools and unscrewed it from the cooker lid. I replaced the weight with a brass ¾ mpt fitting and used hard copper line to attach the fitting to a ball joint and a quick release coupling. (Before I use this for more than testing I will also plumb in a 150 psi safety valve).
From the quick release coupling I attached an air tool line – I looked into using soft copper ¼ tubing, and even though the burst pressures were 900psi which was plenty strong enough, for testing I wanted the flexibility of a hose.
When filling the pressure cooker/boiler do not overfill it, don’t go more than 1/3 full or you could have dangerous overpressure. Believe me just a small amount of water will run weed eater steam conversion a long time, especially considering this is something you cannot fire and forget. If you have heat to your boiler you HAVE to be present at all times.
So in closing, a pressure cooker makes a pretty decent steam boiler, but you have to take into consideration the strength of all the components and realize that you are dealing with extremer heat and pressure, and if a failure occurs it will be at the weakest link. You have to think through the process and ensure that precautions are taken to keep that weakest link in a safe place.
Please watch the video, as it will explain things a lot better, as well as show the engine working.