Keg King Inline Regulator via William’s Brewing. About: “This in line regulator features 1/4″ hose barbs, and can be adjusted with a flat head screwdriver. It can reduce incoming pressure from 150 PSI to 1 PSI. It is very handy to use when you want to use a single output C02 regulator in a draft system, but supply different kegs with different dispensing pressures. 4.75″ long with included brass hose barbs installed.”
This is basically an inline secondary regulator. You still need a primary regulator attached to your CO2 tank. The idea is, you set the primary to the highest pressure you will use (without exceeding specifications of any component of your system) and then use these regulators inline (one per line) to fine tune pressure and carbonation [See: Balancing Your Draft System]. As an example, you could set your primary to 25 PSI for faster force carbonation and set each line to a different pressure based on desired carbonation level.
As of this posting, these are selling for just $8.99. Check site for current price and availability.
The inline regulator is adjusted by a screwdriver and does not have pressure markings or a gauge. You could use something like this inline gauge, manually check pressures with something like this keg pressure tester, rig up something with a t-fitting or (my least favorite) use trial and error.
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