Duotight Flow Stopper Automatic Keg Filler

Stop Guessing When Your Keg is Full

Filling a keg without overflow usually means standing there until liquid hits the gas post. The Duotight Flow Stopper removes that step. Mount it on the keg's gas-out post and it cuts liquid flow the moment the keg is full. A ball float rises with the liquid level and seals the path, so beer or other beverage stops exiting the gas post on its own.

Use it for keg-to-keg transfers, fermenter-to-keg fills, or straight filling from a pump or counter-pressure setup. The shutoff action is the same in each case: fill until full, then flow stops. You don't need to hover over the keg or time the transfer by ear.

How the Float Shutoff Works

Liquid enters through the Duotight push-in path and moves past an acrylic sight glass, so you can see fill progress in the line. When the keg reaches capacity, liquid backs into the gas post and lifts the ball float against its seat. The stainless spring helps the float reseat cleanly when you break the connection and drain residual liquid. There's no electronic sensor and no power requirement—just a mechanical float that responds to liquid level.

Because the assembly uses the Duotight 8 mm push-in system, you connect and disconnect fittings without clamps or tools. Push the tubing home until it seats. To release, press the collet and pull. That matters when you're swapping kegs mid-session or breaking down the setup for cleaning.

Pair With a Spunding Valve for Controlled Fills

Open filling can kick up foam, especially with carbonated beer or when you're pushing liquid hard from a higher vessel. The Flow Stopper pairs cleanly with a BlowTie spunding valve on the outlet side. The BlowTie holds back-pressure on the receiving keg, which slows inlet speed and reduces foaming as the keg fills. Connect the BlowTie to the Flow Stopper outlet with a short run of 8 mm OD EVABarrier tubing. Ball lock fittings and the BlowTie valve itself are sold separately—this kit covers the flow-stopper body and the Duotight adapters you need to plumb it.

If you're running closed transfers under CO2 or nitrogen blanket, head pressure plus the float shutoff gives you a cleaner fill and less product loss at the gas post. Set the spunding pressure for the style you're packaging, start the transfer, and let the float handle the cutoff when the keg is full.

The acrylic sight glass is the window into the fill. You'll see liquid move through the line and know when the float is about to seat. After use, flush the assembly, pull the tubing free of the Duotight fittings, and clean the float and sight glass so residue doesn't stick the ball on the next run.

Practical Setup Notes

Install the Flow Stopper on the gas post of the receiving keg—the same post that would otherwise vent or spill when the keg tops out. Liquid supply still goes in through the liquid post (or your chosen fill path). When the keg is full, liquid reaches the gas post, the float rises, and outflow stops. Relieve pressure, disconnect, and you're done.

Tubing is 8 mm OD throughout the Duotight portions of this kit. Match that with EVABarrier or other 8 mm OD line rated for beverage use. The 5/8" FPT adapters and 1/4 in. flare piece give you options for ball lock tails, gauges, or spunding hardware depending on how you build the outlet side. Keep spare joiners on hand if you reconfigure often; push-in systems reward clean, square-cut tubing ends.

This is a hands-off cutoff for anyone who fills kegs regularly—homebrewers running closed transfers, small taprooms packaging from bright tanks, or shops that move product keg-to-keg without wanting a constant watch on the gas post. It won't carbonate for you and it won't replace a proper counter-pressure filler for bottle work. What it does is simple and reliable: fill the keg, shut the flow, and free you from staring at the post until liquid appears.

Highlights

• Ball float automatically stops liquid at the gas post when the keg is full.
• Works for keg-to-keg, fermenter-to-keg, and direct keg fills.
• Acrylic sight glass shows fill progress in the line.
• Duotight 8 mm push-in fittings—no clamps or tools to connect.
• Outlets pair with a BlowTie spunding valve via 8 mm OD EVABarrier tubing.
• Kit includes float, spring, sight glass, elbow, flare, FPT adapters, and joiners.

What's Included

• 2 × Duotight 8 mm × 5/8" FPT (DUO104)
• 1 × Duotight 8 mm elbow (DUO107)
• 1 × Duotight 8 mm × 1/4 in. flare (DUO106)
• 1 × Ball float
• 1 × Stainless spring
• 2 × 8 mm OD EVABarrier joiners
• 1 × Acrylic sight glass

Specifications