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I am trying to create a prototype for a gravity energy storage system, and I need to release potential energy stored in a heavy load of mass M, raised to a height *H.

I intend to use the mass traversing the length, to drive a piston, which pushes upon a hydraulic fluid to turn the P.E into K.E.

I am at a loss as to what mechanism I can use to efficiently (and simply) translate the descent into a vertical movement of the piston - since the piston will be contained in a sealed cylinder.

I have included a rather crude sketch below:

Mechanism

Where:

  1. The parallelogram represents the load bearing surface,
  2. The two dark circles represent the piston/plunger

My question is this: Is there a mechanism that allows a plunger/piston to be moved along an axis WITHIN a cylinder, by means of external force applied OUTSIDE the cylinder containing the piston?

I think what I'm looking for is some kind of telescopic mechanism.

Homunculus Reticulli
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2 Answers2

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Yes there is, it is a magnetically coupled hydraulic cylinder. Here is how it works:

The piston inside the sealed cylinder is a very strong permanent magnet, sealed against the inside of the cylinder walls with an O-ring or two. the cylinder walls are thin stainless steel through which the magnetic field can penetrate. outside the cylinder is a second set of permanent magnets encircling the cylinder which strongly attract the piston magnet inside, and instead of O-rings this magnet assembly is mounted on a set of linear ball bearing slides. Any movement of the piston inside the cylinder will be translated to the slider outside by the magnetic attraction, and the slider can b easily connected to the machine element of your choice.

niels nielsen
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Energy storage is a fairly common feature in hydraulic systems. Storing energy via nitrogen compression in accumulators is far more cost efficient than storing via mass/gravity. Personally I would just use something off the shelf. Here are a few popular brands:
https://ph.parker.com/us/en/piston-style-accumulators-parker-a-series
https://www.boschrexroth.com/en/xc/products/product-groups/industrial-hydraulics/topics/cylinders/large-hydraulic-cylinders/products-and-features/hydraulic-piston-accumulators/index
https://www.hawe.com/en-us/products/product-search-by-category/hydraulic-accessories/accumulators/hps/
https://www.hydac.com/shop/en/hydraulic-accumulators
I'm highlighting piston type accumulators since you specifically asked for that style. Other varieties such as diaphragm type or bladder type are usually cheaper per kJ of storage. Piston type accumulators are really for specialty applications such as extreme pressure (700+ bar), corrosive fluids that dissolve bladder materials, narrow installation dimensions, horizontal installation (bladder type service life is best with vertical installation), etc.

Note that with any type of energy storage, there are many safety considerations regarding how to dissipate energy in machine failure situations. Don't simply throw together an accumulator + pump + hoses. You need additional valves for pressure relief, accumulator dump, pump outlet check valve, etc. Further reading - https://www.machinerylubrication.com/Read/30331/hydraulic-accumulators-dangers

jrbe228
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