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Then how much pressure is it?


If voltage is like pressure, then how many hydraulic PSI equals one volt? 

Let's make a bunch of assumptions. Looking around on various pages of hydraulic backhoe pumps, I find that a 30 cubic in/sec flow rate pump can run at 1500 psi, transferring about 5 kilowatts. What are the typical hose diameters like? Maybe 1" inside? 

So, if a 5KW DC motor runs at 240v and 20 amps, and if the wires are equal in size to the hydraulic hoses above, then what hydraulic pressure "equals" one volt of potential? 

The speed of the "electron fluid" is slow, but the speed of the hydraulic fluid in the hoses is fast. Pressure will have an inverse change (since watts is proportional to fluid speed times pressure diff.: we must raise pressure while slowing the flow, so that power in both examples is the same.) The speed of hydraulic fluid in the above example is about 30 in/sec.  the speed of charge carriers for 20 amps in 2cm solid copper "hoses" is around .0002"/sec. 

Therefore, if a hydraulic system was flowing at .0002" per second rather than 30" per second, yet was still delivering 5 kilowatts, the pressure would have to be proportionally higher than 1500 psi. 

I make it out to be...

  • 1 volt potential "equals" a hydraulic pressure of 1,000,000 psi

Very rough calculations, lots of weird assumptions, might be off by 2x or 10x. 


Huh. So that's why electrons can flow so slowly in everyday circuitry. The "working pressures" in simple electric circuits are astronomical, when compared to the pressures in hoses in industrial hydraulics. And the resistance of wires is terrible, it's huge: like pumping hydraulic fluid through fine gravel or powder. Even worse than that! Electric circuits are like pumping warm tar through pipes full of packed sand. If it moves fast enough for humans to notice the motion, it would char itself from the frictional heating. Circuitry has high pressure, slow flow, and not much heating caused by excruciating slow fluid-flow in the mile-long tubes of sand, tubes called "the power grid." 

And think about AC power systems. It's not just one volt anymore. Sending megawatts down an AC line is like sending sound energy at 60Hz along a long column of fluid, with the sound pressure being hundreds of billions of PSI, and the fluid inside the pipes only vibrating microscopically back and forth. 

Now if only hydraulics behaved like wires! In that case a hydraulic motor could still turn at a decent speed, even when supplied with extreme mega-PSI pressure and almost no fluid-flow rate. The oil could move at 1mm per hour, while the oil-motor still was spinning at 1000RPM. With a setup like that, the losses in miles-long hoses would be tiny, and we could replace all of our power technology with "hydr-icity pipes" instead of "electr-icity" pipes!


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