Remote gas storage offers flexibility in large and small systems, Figure 5. The gas bottle concept is often described with this formula: accumulator size minus required fluid output equals gas bottle size. For example, an application that calls for a 30-gal accumulator may require 8 to 10 gal of fluid output. This application, therefore, could be satisfied with a 10-gal accumulator and a 20-gal gas bottle.

An accumulator used with remote gas storage generally has the same size port at the gas end as at the hydraulic end to allow unimpeded flow of gas to and from the gas bottle. The gas bottle has an equivalent port in one end and a gas charging valve at the other. These two-piece accumulators can be configured or bent at any angle to fit available space.

The gas bottle concept is suitable for bladder and piston accumulators. Bladder accumulators require a special device called a transfer barrier at the gas end to prevent extrusion of the bladder into the gas bottle piping.

Again, a piston accumulator should be sized to prevent piston bottoming at either end of the cycle. Bladder designs should be sized to prevent filling to more than 85% or discharging to more than 85% empty. The flow rate between the bladder transfer barrier and its gas bottle will be restricted by the neck of the transfer barrier tube. Because of these drawbacks, bottle/ bladder accumulators should be reserved for special applications.

This article was excerpted from the 2010-2011 Fluid Power Handbook & Directory, and updated by Bonnie Trowbridge, of Lightning Hybrids. Contact her at bonnie@lightninghybrids. com or (303) 519-4144 or visit www.lightninghybrids.com.

For more on accumulators, visit our Tech Zones at http://bit.ly/HPAccumulators and our Fluid Power Basics eBook and our Fluid Power Circuits Explained eBook chapters on accumulators.