More for Less with Accumulators

As a prolog to the following let me just say, as I may have said before in this blog, that being an engineer is both a blessing and a curse.  A blessing because you intuitively understand how things work (or at least think you do) that other people see as magic, and a curse because it is not possible to turn off being an engineer, which can be frustrating.  Also, interesting engineering is sometimes found in the least expected places.  This one, which I feel has a potential use in cleaning system applications, I first discovered at Epcot Center in Disney World.  Should I be surprised?

In the center of the Innovations area of Epcot Center, there is a huge fountain which performs in synchronization with music.  Multiple jets of water spurt up into the air at least 150 feet with microsecond timing and cascade back down over the edge of the fountain.  Looking at the fountain (as an engineer) I was at first impressed with the capacity of pumps that must be required to pump all that water.  During a later trip when the fountain was drained for maintenance and the workings were revealed, it became clear to me that the pumping requirement wasn’t as huge as I had at first imagined.  The “trick” is that each nozzle is fed by an “accumulator” consisting of a pressure canister.  During the time that the nozzles are not functioning, the accumulators are filled with water which pressurizes the air within them.  Then, at the proper moment, the accumulated water, pressurized by the trapped air, is released to the nozzle.  In short, the pumping capacity required is only a fraction of what I had first thought since it is water under pressure from the accumulators that actually propels the jets and not a pump.  Since each jet is on for only a short period of time, there is time for refilling and pressurizing the accumulators between bursts.  In fact, this is not unlike a toilet which accumulates water in a tank which is released during flushing in a large volume to achieve the desired result.

Subsequently, it has occurred to me that this same concept might be used in cleaning systems in cases where a relatively large volume of water or water under high pressure (as in a deluge rinse or spraying application) is required for only a short period of time.  Instead of having a pump that can, for example, deliver 10 gallons per minute at a pressure of 100 pounds per square inch, why not have a pump that can deliver 1 gallon per minute at 100 pounds per square inch (at lower cost) and accumulate it for use at the appropriate time propelled by the pressure of air from an accumulator?

Accumulator System
In the lower of the two illustrations above, a short burst of high pressure liquid can be supplied using a lower capacity pump thereby reducing the pump capacity and short term energy requirement as pressure is built up in the accumulator(s) during the time that the nozzle is not in use.

The pragmatist might counter that as the air in the accumulator expands, the available pressure decreases.  Although true, many applications will tolerate reducing pressure.  If not, there are a couple of options.

  • Size the accumulator(s) so that the pressure will be adequate even despite the pressure drop at the end of the anticipated requirement.  This can be accomplished by increasing the size or number of devices.
  • Pressurize above the required pressure and use a pressure reducing valve to control a constant pressure to the nozzle.

Again, I believe this arrangement has potential use in cleaning system applications where significant amounts of liquid are required for only a short period of time.

–  FJF  –

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