Since Windward's B2M research is funded either internally or by True Fans of this work, our primary focus is on what can be done with mass produced materials that are appropriate for re-purposed applications. The major exception is when safety concerns require new or purpose-designed materials. For example, it's fine to use rebuilt hydraulic cylinders for compressing air, but not for compressing pure oxygen.
We're especially delighted when we can repurpose materials that otherwise were on their way to the landfill or to be melted down as scrap metal.
the blue tank is a bladdder-type water pressure tank
Twenty years ago, water pressure tanks would start off empty with water entering and exiting the bottom. As the pump built up pressure, the air above the water would occupy a progressively smaller volume. When water was drawn out, it was that air pressure that pushed the water through the pipes to the point of use.
These days, water pressure tanks commonly contain bladders that are similar to the rubber inner tubes that tires used to use to maintain air pressure. They even have the same sort of inflation stem that you find on inflatable tires. This allows the pressure tank to be precharged with compressed air, thereby allowing the tank to function as though it were a notably larger tank.
After some period of service, it's common for the bladder to fail. Given the disposable mindset of the mainstream culture, instead of replacing the bladder, what most people do is to have a plumber replace the entire unit. Consequently, the metal shells are a common and readily available component of the waste stream.
While the most common household water pressure maxes out at around 4 bar, these bladder-type storage tanks are rated for pressures up to almost 6 bar. That makes them ideal for use as pressure accumulators at the output of the first stage of the hydraulic compressor.
Another example of obtainium for low pressure applications is an obsolete home-heating oil tank which we can use to hold the heat transfer fluid (HTF) that will use store heat gathered using solar collectors and used to drive a flash boiler.
a TLUD gasifier made from a 25 gallon propane tank with a heat shroud made from a water pressure tank
Once appropriate precautions have been taken to ensure that all combustible materials (such as propane vapors) have been displaced with non-combustibles (such as water), cylinders that originally held propane can be cut apart and welded back together in a variety of useful ways. One thing that should not be done with a former propane cylinder that been cut or welded is to attempt to return it to use as a pressure container. Because it's been modified, it's not a propane cylinder any more‒it's just a useful form of scrap metal.
And appearances can be deceiving--the fact that a pipe fitting (for example) can screw into an application is no guarantee that it can handle a higher pressure than it was designed for. When using obtainium, it's very important to take advantage of the "known characteristics" aspect. In this age of the Internet, there's really no excuse for not taking the time to look up the specifications on components you're thinking of using in some novel way.
