Pressure Fermentation Device - Homemade

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Active Member
Jan 20, 2023
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Southeastern US
Hello BrewCrew!!

I had a brainfart idea this morning, that I thought I would share with y'all. This will work really well with bucket brewing, or Fermonsters, etc.

This will also serve as an Airlock Bubbler and Blow-off Tube.

Materials needed:

A) 2x4's, woodscrews or nails, hammer or electric screwdriver, saw and measuring tape (6ft min) - for building a "Fermenter Platform" and "Tubing Frame".

B) 1/2" ID clear or translucent brew tubing or food/water safe tubing. For 2 psi fermenter pressure, your going to need about 20 ft.

C) Smallish container with sanitizer in it for the air seal and possible Blow-Off collection.

D) Hose clamps or zip-ties to secure the tubing.

General Instructions:

1) Build the Fermenter Platform in whatever style and height you like. It can be as fancy or simple as your creativity, space and budget will allow. But, as a example, let's use 5" off the floor - base 2x4 on edge (3.5") with 2x4's flat (1.5") on top of the base for your Fermenter to sit on... think wooden pallet style. For me, I'm thinking 24"x24" square for a 5 gallon to 7 gallon bucket.

2) Add two verticals to the back of the platform to support your tubing. These need to be well secure to the platform and braced, but they could be 2x2's instead of 2x4's. They should be about 60" long.

3) Add a horizontal brace (HB) across the top of the verticals

4) Attach the tube to the top of the Fermenter and take it over to one of the verticals and attach with clamp or zip-ties. Run the tubing up to the top of the vertical and attach it at the top with a clamp or zip-tie.

5) Let the tubing run about 6" across the HB and attach with clamp or ZT.

6) Let the tubing droop down about 65" and back up to the HB about 12" from the previous attachment point and attach with clamp or ZT. You have now created a long "U Tube" in the middle of the vertical frame.

7) Run the tubing over to the other vertical and down that same vertical so that it will reach your sanitizer container, which will probably be on the floor. You have basically made a large manometer. Roughly an M shaped tubing run with SMOOTH BENDS... NO KINKS.

8) For this step you will need to temporarily disconnect your tubing from the frame on the exit side... Using a funnel or large syringe - turkey baster ? - fill the tube with sanitized water until you have a column that is about 27" tall from the bottom of the U to the top of the water column. There should be two equal "vertical" water columns, 27" tall from the bottom of the U. MEASURE VERTICALLY... NOT ALONG THE LENGTH OF THE TUBING. Mark your tubing levels for future use, but always double check your water column heights from the BOTTOM OF THE "U" (NOT THE FLOOR).

The CO2 pressure in your Fermenter will have to push the water column down on the "entrance" side until you have about a 54" tall water column on the "exit" side. This equals approximately 2 psi. Just like a bubbler, when the pressure exceeds 2psi, some of the CO2 will "escape" around the bend in the U tube and the press will drop back to about 2psi, and the cycle will repeat itself until fermentation slows to where you are not making enough CO2 to bubble anymore... and, assuming no leaks, you should still be holding about 2psi on the fermenter.

14.7psi = 33 feet of water column (Not exact but very close.) ==> 33ft/14.7psi ~ 2.25ft (27") of water column per psi. Therefore 2psi x 27" = 54" of water column.

At 2psi, you should still have about 8"-11" of clear space above your water column on the exit side. You can design this to have more, if you like; it's just more height and tubing and frame.


1) Be sure to use smooth bends with no kinks.
2) You can use any combo of Beer Tube, PVC, PEX, rubber hose etc. But the Middle "U" Tube should be translucent/clear so that you can see the water columns.
3) Any size tubing will work. A 33ft water column is always only about 14.7psi static pressure regardless of diameter/size. E.G. a pressure gauge in the ocean at 33ft below the surface will measure about 14.7psi, and a pressure gauge on the end of a vertical piece of 1/2" ID Pipe, 33ft tall, full of water, will measure about 14.7psi. Altitude CAN have an effect, but, for our purposes it is negligible.
4) I would recommend a minimum 1/2" tube size for the system: easier to clean and, if necessary sanitize.
5) This system ASSUMES that you have NO GAS LEAKS in your fermenter or lines. If you do, you will not maintain the 2psi design pressure.

I will try to upload a sketch, for those that are interested. But please be patient... I do have a fulltime job... and yes, I are an Inguneer! :D:D:D

Fire away with questions. I'll try to answer in a timely manner.

Good Brewing and God Bless!

Last edited:
Interesting idea. I think you would have to keep a very close eye on the fluid level in the U bend. I have noticed when this same situation happens spontaneously in coiled tubing, the escaping CO2 tends to carry away some of the liquid over time and eventually the U runs dry. Might help to make the tubing as large ID as possible to increase the total amount of liquid acting as the airlock.
Out of curiosity, what is this trying to accomplish that a plain blow off tube into a jar of sanitizer can’t do?
I’m no expert on fluid pressure but couldn’t you just run a blow off tube into the bottom of a tall vessel filled with water or sanitizer like an empty corny keg?
With large Dia tubing, @Whisky River , I think it would work, but I too would worry about "push out". StarSan often bubbles out but that specific substance is built to make sustaining bubbles to eek into small cracks and areas, whereas water has diff surface tension. I was thinking use a bit of PVC pipe as the part holding the water column. But then you're really Rube Goldberging connections of tubing to the bottom, etc. And even if two swallows carried it between them with a bit of creeper, it's still more trouble than running ferment gas through an empty keg to CO2 purge it during fermentation, and put a spunding valve on the output of the keg. One Monty Python fan's opinion, of course.

[Edit: and you beat me to it. But you didn't have creeper. So I win.]
I’m no expert on fluid pressure but couldn’t you just run a blow off tube into the bottom of a tall vessel filled with water or sanitizer like an empty corny keg?
^^ what he said. If I understand, the goal is to create a 54" vertical column of liquid for back pressure. Can you get a piece of 4" PVC pipe, cap one end, and fill to 54" ?
Must have the "M" or "U" shape. Acts like an S trap to prevent water column from flowing back into your fermenter.

OR.. put the BOTTOM of your fermenter 27" above the bottom of your 54" tube... Actually that's a great idea... Makes the system simpler. But still creates the "U" shape in the tubing.
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I edited my last post, because I realized I had made an error.

For a simple manometer, you cannot have different ID's of your vertical legs. That would create a differential volume, such that 1" of movement in one leg would NOT = 1" of movement in the other leg. Example: 1" ID on entrance tube and 2" ID on exit tube would create a 4:1 hydraulic ratio (πr^2). Entrance height would have change 4" to cause a 1" change of the exit height.

Sorry for the confusion. I got caught up in the idea and didn't do the math first.

Good Brewing and God bless!


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