Inline Flare Check Valve via William’s Brewing. About: “This German-made one way gas check valve features 1/4″ threaded flare fittings, to fit standard threaded ball and pin lock gas connectors. Prevents beer from backing up into gas lines. This releases at 3psi, and is a great way to add a one way valve to your threaded ball or pin lock keg connector.”
As of this posting, this is selling for $9.99. Check product page for current price and availability.
William’s Brewing also carries a Gas Ball Lock QD with a built check valve – CMB GAS BALL LOCK FITTING WITH CHECK VALVE
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