How to Set and Adjust a Spunding Valve for Pressure Fermentations

Spunding valves are a relatively simple but crucial bit of equipment when dealing with pressure fermentation. A spunding valve allows you to set a predefined level of pressure within your pressure fermenter which the valve will maintain by venting or releasing any pressure above this predefined level.

Kegland Blowtie Spunding Valve fitted to a keg

What Does a Spunding Valve Do?

A spunding valve is a device used in brewing to control the pressure within a fermentation vessel, such as a keg. It allows you to maintain a set pressure by releasing excess gas if the pressure exceeds the desired/preset level.

Example Scenario

If a spunding valve is set to 10psi, it will not vent any gas and allow the pressure inside the vessel to build up to 10psi after which it will begin venting any additional air/pressure that builds up so a steady 10psi is maintained throughout the fermentation. This pressure build up occurs as one of the byproducts of fermenting yeast is carbon dioxide gas (CO2).

Our Spunding Valve

KegLand Blowtie Spunding Valve

The spunding valve we'll be using is the KegLand integrated gauge blowtie spunding valve - if you have a different make/model it won't be a problem. The underlying process will be the same regardless of what type of spunding valve you have.

We do find it a little easier with the KegLand Blowtie - since you can attach a length of hose to the outlet of the valve which makes detecting when gas is being vented a little easier.

Blowtie Built-In Gauge Inaccuracy

Before we start - we've noticed on that the built-in gauge on the Blowtie spunding valve is very inaccurate, so we won't be using it as a reference point for our vessel pressure. Instead, we'll be using the low pressure gauge on the CO2 regulator attached to our gas bottle.

The built-in analog gauge is known for being inaccurate

If you're using the Blowtie, another good option is to upgrade to a digital built in gauge which is much more accurate

Blowtie Orientation

It's also worth pointing out on the Blowtie spunding valve we're using is an arrow on the side indicating the direction gas should be flowing through the valve. If you're using one of these, make sure you have it installed the right way otherwise it won't function correctly.

Note the arrow circled in black showing the direction gas should flow through the spunding valve

Instructions To Set Your Spunding Valve

1. Assemble your Spunding Valve

• If your spunding valve is brand new, make sure it's assembled and ready to use

2. Pre-Pressurise your Vessel

• Pressurise a keg or other pressure-capable vessel to the pressure you want to set your spunding valve to. A good starting point for pressure fermentations is 10psi. As previously mentioned, we use the low pressure gauge on our CO2 regular to set this pressure in the vessel as it's far more accurate than the built in gauge on the spunding valve.

The Blowtie spunding valve with digital gauge upgrade

• You can use a PCO 1881 carbonation cap tee piece (like this) in order to be able to use a smaller soft drink bottle instead of a 19L keg to save on your gas usage).

3. Close the Spunding Valve

• Ensure the diaphragm on the spunding valve is fully closed (so it won't vent any air/gas). 
• On the Blowtie this is achieved by winding the adjustment handle clockwise as far as it will go.

4. Attach the Spunding Valve

FermZilla All Rounder with Blowtie Spunding Valve attached

• Attach the spunding valve to the gas post of your keg or carbonation cap tee piece. There should now be a reading on the gauge of your spunding valve showing it has pressure (hopefully around 10psi).

5. Attach Outlet Hose

• If you're using a Blowtie spunding valve, attach a short hose piece to the outlet of the spunding valve and submerge the end of this hose piece into a glass of water.
• Alternatively, you can use foaming sanitizer such as StarSan or StellarSan instead of water.
• You can also use a soda bottle with a carbonation cap t-piece attached like in the picture below.

Blowtie Spunding Valve attached to a soda bottle using ball lock disconnects

6. Open the Spunding Valve

• Begin slowly unwinding/opening the diaphragm adjustment on your spunding valve until you start to see bubbles in the glass of water you have the hose piece submerged in.
• Bubbles appearing is an indication that gas is being released/vented by the spunding valve. 
• On the Blowtie spunding valve, this adjustment is done by slowly turning the yellow handle anti-clockwise.

Bubbles appearing indicates the valve is venting at the set pressure

• If you're using a different type of spunding valve, you can spray soapy water around the outlet of the gauge, or simply listen for gas escaping.

7. Make Final Adjustments

• Once you see the bubbles appear (or hear gas escaping), you know the valve is releasing pressure at 10psi - or whatever pressure you pre-set on your vessel. 
• You can continue to make tiny adjustments on the spunding valve again to close it until the bubbles stop. This way, it will begin releasing once pressure exceeds 10psi, not at 10psi.

8. All Set

• Your spunding valve is now set. Take care not to bump/move the adjustment on it when disconnecting, storing or reconnecting. 
• Even slight adjustments on the dial of the valve can result in big changes to the set pressure.
• If in doubt, check/adjust the spunding valve again.

Conclusion

Spunding valves are an crucial piece of equipment when dealing with pressure fermentation. Adjusting them is just as important in order to ensure the pressure within your fermenter doesn't exceed the manufacturers recommendation.

If the pressure inside were to build up too high, it could detrimental to yeast health and potentially lead to damage to the fermenter. Most pressure fermenters have a pressure relief valve (PRV) as a safety net to prevent this from happening as well.

Thankfully, the process for setting and adjusting your spunding valve is fast and easy, so we recommend it be done every time you're attaching your spunding valve.

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