I talked to a gentleman yesterday about hydropnuematic flushing. They made their own machine, using the picture in NFPA 13 as a guide.
The machine was made from an air compressor with the compressor removed. A fitting were welded on the top of the tank for a compresor connection. Garden hose fittings were welded lower on the tank. The end of pipe fitting was removed from the pipe and a garden hose fitting and a shut off valve was installed. NFPA 25 2011 Edition, Fig D.5.4a shows the machine. Hydro testing the machine prior to use would be a good idea.
The main control valve was shut and the main drain was opened. The clapper was was removed or latched open. The end of line valve was opened and 100 PSI of air was pumped into the lower tank. The water under pressure removed the rust and scale from 10 pipes at a time. Amazing what one can learn by attending a class.
We have flushed a couple of systems using garden hoses, not backflushing. We ran the hoses outside. We have found 1", 1.25' and 1.5" pipes plugged solid with rust. We have also found you need to make the customer aware that when you remove the rust and scale, you may develope large enought leaks to soak through sheet rock and tile very quickly. Have plastic sheeting ready to cover equipment.
You should have pipe, fittings and the equipment ready to machine pipe as needed. Make sure your contract protects you against leaking pipe.
We paint the ends of the flushed and/or replaced pipe with white paint. We then use a magic marker to write the date,company name, and what we did on the fresh paint.
Google "Hydropneumatic Flushing"