Hello All,
I’m a new poster. A couple of years back I figured out that I love working in, designing with and contributing to the natural world. Then, I discovered the term “permaculture,” and my eyes were opened. I love this site.
Now, down to the question. I have an engineering and medical background, for reference. I have also had the question about how deep to make a trompe that will produce a useful pressure. It is absolutely true that lower pressures like 30 or 40 PSI can be very useful around the homestead, but in my experience most pneumatic tools run on an average of 90 PSI, with varying flow rates. Flow rate is one of the things that really excites me about trompe technology. Because it is powered by a running (I.e. constantly replenishable) water source it is always compressing air, 24 hours a day 7 days a week. If you hook your trompe to a grid of air tanks (WITH APPROPRIATE PRESSURE RELIEF SAFETY VALVES) then you can potentially store massive amounts of useful mechanical power for free. “Mind-blowing!”
For me, a minimum of 90 PSI would be the goal. You will have to consider the needs of your homestead. As I understand it, the weight of the water atop the air bubbles is what causes the gas compression. To find our pressure, we are interested in the weight the water sitting on the air at the bottom of our system.
Here is a useful website for reference:
https://sciencing.com/convert-water-column-pounds-pressure-5666070.html
At the bottom of a column of water, a predictable pressure is generated. If you are looking at a “stack” of water molecules sitting in a hole in the ground, a pipe, or a garbage can, the 3D shape of the water doesn’t matter. It’s the height from top to bottom that matters, “head height”. Your water feature could be shaped like an upside down pyramid or a vertical pipe, but so long as they are the same height, “top to bottom” they will generate the same amount of pressure. It’s very counter intuitive.
At the bottom of a water column that is 27.78 inches tall you will create 1 PSI. Every time you go another 27.78 inches down, you pick up another 1 PSI.
So...... 90 PSI x 27.78 inches = 2500.2 inches
2500.2 inches / 12 inches per foot = 208.35 feet. 210 feet for safety in calculations.
As far as I can figure, if from the point that your water starts falling down the tube to the point that it hits the bottom of your tank inlet pipe is 210 feet, then you will get a steady stream on cool, dry, 90 PSI+ compressed air. That’s awesome!
Putting your system that far down presents some challenges, but personally with enough land, I think that is attainable for the DIY homesteader. I’m still brainstorming on the how tos, but I think with wise planning, persistence and some bravery, a lot of us can get there. May God bless your efforts.
