Power Water Networks
lowtechmagazine.com
lowtechmagazine.com
Other relationships are inverted. Electricity must be generated continuously. Unused generation is wasted. Hydraulic pressure is retained in a system (absent leaks) until tapped, a periodic re-setting of a concentrator load is sufficient to re-charge the system. Tremendous forces can be made available over wide areas with little energy input.
Oh: and city-wide grids of this existed. Until the 1970s in some cases.
Not quite: You can use a capacitor to store electrical energy. In fact, a capacitor corresponds to a water tower in the electricity/water analogy.
Turns out caps are kind of hard and expensive and finnicky. But yes, that's the analogue.
700 psi is enormously high compared to current municipal water systems which rarely go over 150 psi. Maintaining and working on a pipeline of this size and pressure is more dangerous and very expensive. Over time, age will cause the network to lose pressure(through leaking, scaling, etc). How can facilities maintain power when a main line breaks? They would need their own water supply, tank and pumps in lieu of a diesel generator.
Electrical systems are generally much easier to install and work on. Piping is underground, large (compared to transmission wires) and much more prone to failures. A powerline going down can cause an inconvenience for a few days at most, but a broken water main will flood everything in its vicinity.
Also where will the water be sourced from? Municipalities are permitted to only draw a certain amount from their water supplies. This will definitely cause contention especially in drought conditions.
As with electricity, hydraulic circuits are high-pressure, low-flow, and are largely self-contained. An advantage of water-based hydraulic systems over synthetic hydraulic fluids is that the water can be bled from the system without contamination. But these are pressure rather than throughput systems. Actual water draw is minimal.
Pipelines themselves are small -- an inch or two in diameter. Not much larger, if that, than electrical conduit.
You're almost certainly right that there would be ongoing maintenance issues over time. Subcircuit isolation would have to be part of this, as well as perhaps redundant pressure circuits.
Early designs were widely distributed because prime movers / energy sources were scarce. We do use hydraulic systems extensively today, but they're largely small and self-contained. An automobile braking system, front-end loaders or other construction equipment, elevator systems, and the like.
A thought is that such systems would be useful, on a localised scale, where energy inputs are variable, but uses are relatively occasional. A home or factory power hydraulic system could operate small or occasional machinery (lifts, presses, punches, door mechanisms) without requiring 24/7 electrical supply.
I also recall that the Amish make use of air-powered tools in certain situations, possibly not unlike those described here.
http://www.heindl-energy.com/hydraulic-rock-storage/overview...
Another avenue is compressed-air energy storage (CAES). Here the problem is Boyle's Law: compressing a gas heats it. Over time, that heat will leak out through containment walls (even in underground spent gas field storage). Releasing the gas cools it, to the point that icing over of equipment is a problem. One solution is to introduce a natural gas (or biogas) jet to the release stream, with additional heat of combustion not for energy so much as to prevent icing.
This scales in theory, though it's still a tad complicated.
To that point I'll respond with a quote from Hendl's site: A storage with a radius of 250 meters could store 124 GWh, which would correspond to the worldwide storage capacity of all pumped storage power stations.
http://www.heindl-energy.com/hydraulic-rock-storage/idea-fun...
There are literally millions of these in Asia, for exactly that reason (pressure fluctuations).