A spending valve is an adjustable pressure relief valve with a gauge attached to show internal vessel pressure. The relief valve can be adjusted to release pressure from 0 ~ 60 psi.
Homebrew Applications of a Spending Valve:
1) Pressurized fermentation. Ferment is a 5 or 10-gallon corny keg and uses your spending valve instead of an airlock. This allows you to ferment at your desired pressure.
2) Dry hop under pressure. This allows you to dry hop earlier while reducing oxygenation. Active yeast is more likely to metabolize oxygen that’s introduced during dry hopping during active fermentation. Since CO2 is not exiting beer as vigorously under pressure, wanted compounds, flavours and aromas are more likely to stay in your beer under pressure.
3) Naturally and accurately carbonate beer right in the keg.
4) Keg to keg transfers. Use the spending valve to allow excess gas to exit the receiving keg as you transfer under pressure. Helps you achieve a slow, controlled and pressurized transfer.
5) Test for keg leaks. Pressurize your keg to serving pressure. Put the spending valve on and note the reading. The gauge should remain steady. If pressure drops, you know you have a keg leak.