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Job van der Zwan


Funny that you post this just as a Hydraulic Press channel on youtube is going viral.




A great read as usual !

Jim Baerg


For another use of hydraulics see:
I've stopped & watched it operate a few times when driving through that part of Ontario.



Interesting article (as usual! was never diappointed here).
When you write your next chapter about compressed air, will you be writing about "trompes"? I have seen some non-scientific posts about the "trompe", but nothing else yet.



Thanks for yet another insightful, well-researched, and thought-provoking article.

You articles remind me of the "Connections" television program hosted by James Burke




As electronic and electric equipment is so advanced and available off the shelf a competing power network will not have a chance. Electricity will be needed anyway.

Hydraulics are used in car jacks, automatic transmission and in many tools or machinery. And on many construction vehicles such as excavators there is a motor driving the hydraulic pump while forward movement is by hydraulic motors and equipment is driven by hydraulics too.

I was in an amusement park and they run many small excavators from one hydraulic pump. So hydraulic power transmission is still in use today although with oil as medium and not city wide.

For any alternative energy conversion of existing hydraulic equipment is easier as only the hydraulic pump has to by replaced.



At construction sites, workers use pneumatic nail guns, not electric. Car mechanics will use impact wrenches. Very local power networks.

And the Amish convert many electrical tools to pneumatic. They last longer too.



The page I wrote about compressed air on the OSE wiki:



I need to make a hydraulic accumulator for my rain barrel!

William Couper


In Newcastle upon Tyne the Swing Bridge, built at the Elswick works of Sir William Armstrong nearly 150 years ago, is still operated using a hydraulic accumulator of water. It is now recharged using an electric motor. The system uses a small motor to accumulate the large amount of energy that is used to swing the bridge. It spreads the load and uses a much smaller and less expensive motor.https://en.wikipedia.org/wiki/Swing_Bridge,_River_Tyne

Boris Doderer


Hello Kris,

a great article. A modern usage of hydraulic power for lifting purposes is todays Mannheim Planetarium. When it was built in the 1980's, the lift mechanism for the lowerable star projector was built to use the groundwater pressure of the planetarium's location. No electricity necessary, and no noise during the shows. Sadly, I can't find any information about its construction.

Concerning your proposition to rethink the use of water hydraulics today:
We have electricity eveywhere, starting with lighting. Even electrical installations for heavy duty purposes are by several magnitudes lighter and smaller than applications for pressurized water to provide the same amount of energy. Installation and maintenance are much easier to be done with cables than with pipes. Not to mention the danger of leakage and pipe burst and the consecuting damages.

Water based hydraulics are a most interesting topic, but I think today their use will rather be limited to exotic individual cases as the one I mentioned above, than as a standard application.

Paul Holden


When I started at the Metro Cammell railway works in 1988, the hydraulic system was still present in the buildings but had not been used since the early 1980's. A large brick tower contained the accumulator weight and piston and a header tank for the pumps.

There were two 500 kW electric pumps each using three cylinder reciprocating machines which kept the accumulator charged. The water main was used to operate the forge shop presses, which made the steel beams for specialist railway vehciles like "well wagons", or London Underground trains.

The current Piccadilly and Bakerloo line trains still have structure made on the water powered presses. The older staff told me that expriments were made to convert one of the presses to modern oil hydraulics but they found it was too slow when compared to the old water system, there is sometimes no substitute for a lot of stored energy.

I find in 2016 engineering that we often have to resort to fabricated designs because so few people can forge or cast large objects like they did in the 20th century.

Paul Holden


You have forgotten Joseph Bramah's most important hydraulic work - the beer engine


Herman Vanmunster


I calculated the storage capacity of Armstrongs' hydraulic accumulator which is described in this article and came to the very stunning conclusion that only 3 regular 12V batteries are needed to store the same amount of energy as Armstrong's accumulator with its 100 tonnes of ballast and 7m stroke ! That immediatly shines another light on the ecological footprint of hydraulic accumulators. I saw foto's of ballasts made of metal. Metals are much to precious to be used as dead weight. Considering the huge amount of energy which is needed to mine ores and draw metals from it, we must conclude that the ecological footprint of such an installation is much to high to be acceptable. If sand or rocks are used as ballast (provided that they are available locally), then the footprint will decrease dramatically, but the volume of the installation will increase likewise. So the conclusion could be that this type of accumulation is only acceptible if we are able to reduce our hunger for enegry so dramatically that we don't need to store huge amounts of energy.

Energy capacity of the battery:
A regural battery as used in common cars has a storage capacity of 50 Ah (= 50 Amps can be delivered during 1 hour while the battery maintains its 12V output). Thus such a battery can deliver 12V x 50A = 600W during 1 hour. 1 Watt = 1 Joule per second. So 600W x 3600 seconds = 2,160,000 Joules stored in 1 battery.

Energy capacity of the hydraulic accumulator:
For potential (gravitaional) energy the formula is:
Energy (Joule) = m x g x h, where m = the mass in kg, g is the gravitational acceleration (= 9.81 m/s2) and h is the height of the mass in meter. The ballast weighs 100 tonnes = 100,000 kg. The stroke of the accumulator = 7m max. So the maximum amount of energy that can be stored is:
100,000 x 9.81 x 7 = 6,867,000 J

Both relate to each-other as : 6867000 / 2160000 = 3.18.
So only 3 small car-batteries are needed to store the same amount of energy as the 100 tonnes installation.

kris de decker


@ Herman

That's correct, I made the same calculation before. But if you make a comparison between electric accumulators and hydraulic accumulators, there are more things to take into account. One: lead-acid batteries have to be replaced every few years, while a hydraulic accumulator could last for a century or longer. Second: the charging/discharging efficiency of a hydraulic accumulator is 98%, while for lead-acid batteries it's 70-80%. Three: electric batteries lose energy when they are not in use, but there is no self-discharge in a hydraulic accumulator.

The difference between electric and hydraulic accumulators is thus considerably smaller than your calculation shows.

That doesn't take away the fact that electric accumulators are better energy storage devices than hydraulic accumulators. In the nineteenth-century high pressure systems, hydraulic accumulators mainly acted as regulators of pressure and water flow, their storage power capacity being much smaller than that of a water tower.

The hydraulic accumulator excells at force multiplication, not at energy storage. It is a much better force multiplicator than the electric accumulator.

Herman Vanmunster


Thanks Kris for clarifying this.

I am still convinced that a metal ballast is a bad idea from the ecological point of view because a huge amount of energy is needed to produces 1 kg of iron or any other metal. Things change when the ballast is made from material that is locally abundant and easy to retreive: sand, ground, stones, rocks, etc...

This hydraulic accumulation is a very interesting topic to brainstorm about!

Boris Doderer


@ Herman

Using rocks or stones as a weight surely seems to be the most ecological way to do things, considering their production. But how about the design of the whole system? A stone weight will be rather large in size. It needs an additional structure for balance, guideway and support. With iron as a weight, the whole design becomes much smaller and simpler, which will again save energy in its production. Not to mention the cost being ALWAYS involved in things.

When iron is a material being produced in abundance, it is perhaps more ecological to cast a few extra blocks in the iron foundry around the corner than putting someone to the task of breaking stones somewhere in the country and transporting them by long distance to where they are needed.



In the port of Trieste, Italy , this system for 100 port's crane and 50 goods lifts worked till 15 June 1988. http://www.archeologiaindustriale.org/cms/la-centrale-idrodinamica-del-porto-di-trieste/



Aún estamos esperando el artículo acerca de la trasmisión de energía mediante aire comprimido.



Dear Authors,
Thank you so much for your astonishing work on low-tech!
I have a question.
I plan to mill wheat in my farm (with stone mills), with a dream: not using any electric energy.
I think direct water power is a promising way to do so, as direct wind mills have strong disadvantages due to intermittence when you are no a full time miller. And unfortunately, I live in a flat region with no posibility of wheel water mills.
So, water power seems a nice way to do so, because relying on height is hopeless to have the required power.
Do you know any of such experience in small farms (and not at an industrial level). I understand that this technique need a close system. Is it possible to have the same demultiplicators in an open system? I guess I have to revise my physics.
Your faithfully



There is one more advantage to electric power transmission, that has to do with powering moving vehicles like trams, trains and trolleybuses.



One advantage of water power networks I have not seen discussed is that if the source for pressurizing the water is not electric, or internal combustion powered, the water power network would not be vulnerable to EMP attack, or disruption from powerful solar flares, as current electric power grids are.

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