Nothing Feels Better than Pressure Relief
Another bad gas joke. The latest blockbuster film? Sorry, I’m talking about the mundane, but much more important, topic of tank pressure relief in breweries.
Beer vessels usually operate at a modest pressure, typically around 1 atmosphere above normal pressure, what we call 15 psig, bright beer tanks possibly up to 30 psig. The manufacturer constructs tanks to a higher pressure than is expected in normal use as a margin of safety, say 2-4 times the operating pressure. Tanks may be tested to a test pressure of 1.5 times the operating pressure. While some tanks are ASME-rated, most simply come with a manufacturer’s statement.
It is up to the brewer to make sure the tank pressure never exceeds the test pressure, or else a catastrophic rupture of the tank could occur. To help avoid this, tanks should always be fitted with at least one pressure relief valve (PRV) set to maximum operating pressure, i.e., less than the test pressure. The PRV device is normally mounted to the tank with a standard tri-clamp fitting, commonly on the dome or on the CIP sidearm.
PRVs come in two varieties: spring-loaded valve and rupture disk. The spring type opens to relieve pressure when the pressure is high enough to push a rated spring. Some PRVs are factory-set, while others are user adjustable. Spring-type PRVs open and close as needed, hence are reusable. With a rupture disk, a frangible disk of steel splits open and needs replacement as soon as the pressure problem is resolved.
Some PRVs can also act like a vacuum relief valve (VRV). Certain transfer and cleaning mistakes by the brewer can create a vacuum in the tank — the result, the vessel crumples like a very expensive beer can. All beer vessels should have protection from both excess pressure and vacuum.
Two other essentials are gauging and cleaning. Fit every tank with a pressure gauge, typically 0-30 psi, and follow a frequent cleaning regimen for the pressure devices. There have been serious tank failures that were due to residue in the PRV causing the device to stick. Keep in mind, without proper pressure protection, your day could either really suck or really blow.