Pressure Relief Valve Testing and Calibration

Last updated: May 28, 2026

Pressure relief valves (PRVs) are the last line of defense against catastrophic fermenter or keg failures in a pressurized homebrewing system. I learned this the hard way when a stuck PRV on my pressure fermenter failed to open during a vigorous fermentation, the fermenter held, but it was pure luck. After that incident I developed a systematic approach to testing and calibrating every PRV in my system before each brew, and I’ve never had another close call. Correctly set and maintained PRVs are what separates a safe pressurized system from a pipe bomb.

Types of PRVs used in homebrewing

Spring-loaded inline PRVs

The most common type in homebrewing, a spring-loaded ball or disc held against a seat. When system pressure exceeds the spring force, the valve opens and vents gas. Set pressure is determined by the spring preload. Common ratings: 15 PSI for standard fermentation, 30 PSI for pressure fermenters, 45–60 PSI for carbonation rigs. These are rebuildable and the set point can be adjusted by changing the spring or adjusting the preload nut.

Spunding valves (adjustable PRVs)

Spunding valves are adjustable PRVs with a dial or knob for set-point adjustment and typically a gauge to display current pressure. Used for carbonation during fermentation (natural carbonation by sealing the fermenter at the end of fermentation and allowing CO2 to dissolve). The set point drifts over time as the spring seat wears, recalibrate spunding valves at least annually or whenever carbonation results seem off.

Testing PRV function

Bench test method

1. Remove the PRV from the vessel or line it’s installed on.
2. Connect to a regulated CO2 source through a tee with an accurate pressure gauge.
3. Slowly increase pressure from 0 PSI while watching the gauge.
4. The PRV should open (audible hiss or visible gas release) within ±2 PSI of its rated set point.
5. Reduce pressure, the PRV should reseat cleanly with no continuous bleed at 10–15% below the opening pressure.
6. If the valve opens too early, too late, or doesn’t reseat cleanly, disassemble and inspect.

In-system test

For installed PRVs, pressurize the system to just below the PRV set point with CO2. Gradually increase pressure while watching a gauge teed into the same line. Mark the pressure at which the PRV opens. Compare to rated set point. A PRV that opens 5+ PSI above or below rating should be replaced, a PRV that never opens under any pressure (stuck closed) is the most dangerous condition.

Common PRV failure modes

• Stuck open: PRV continuously bleeds at normal operating pressure. Cause: debris on seat, worn seat or ball. Fix: disassemble, clean, replace seat gasket.
• Stuck closed: PRV never opens even well above rated pressure. Cause: corrosion or hop material cementing the valve closed. Fix: Replace immediately, this is the most dangerous condition. Don’t attempt to free a stuck-closed PRV with the system pressurized.
• Set point drift: PRV opens at significantly different pressure than rated. Cause: spring fatigue (usually opens lower over time), corrosion, scale on seat. Fix: Replace spring or rebuild with kit.
• Chattering: PRV rapidly opens and closes near set point. Cause: system pressure fluctuating near set point, oversized valve for the application. Fix: Adjust operating pressure lower relative to PRV rating, or use a larger relief valve.

Calibrating spunding valves

1. Connect the spunding valve to a regulated CO2 source with a reference gauge in parallel (a calibrated gauge you trust, not the one on the spunding valve itself).
2. Set the spunding valve dial to a target (e.g., 12 PSI for 2.4 volumes CO2 at 68°F).
3. Slowly pressurize until the spunding valve vents. Read the actual pressure on the reference gauge.
4. Adjust the spunding valve’s set screw or dial until the vent pressure matches the reference gauge reading.
5. Retest, repeat until the spunding valve’s integrated gauge reads within 1 PSI of the reference gauge at the opening point.

Common Questions

How often should I replace PRVs?

Replace spring-loaded PRVs every 2–3 years as a conservative maintenance schedule, or immediately if they fail the bench test. Inexpensive PRVs from homebrewing suppliers ($5–15) are not worth the risk of testing to failure, if in doubt, replace. Keep spare PRVs in your shop. After any incident where a PRV opened under high pressure (for example, a fermentation runaway that vented forcefully), inspect the PRV and replace if the seat shows erosion. A PRV that has opened under flow may have debris on the seat that prevents clean reseating.