Your King Fermentor should be pressure tested every two years for your own safety.
The simple way to do this is:
1 Fill the tank completely water and attach the lid.
2 Connect CO2 and slowly increase the pressure until the red safety valve is triggered
3 wait 2 minutes
4 Vent the tank and empty it of water
5 Write the new pressure test date on the tank with marker
The method is approved by Keg King
For the record, King Fermentors come with a 2-year warranty from the date of purchase, regardless of what it says on the tank and whether you pressure test it yourself.
The following is now included with all King Fermentors sold:
Information from Keg King regarding. pressure test date.
The date is NOT a warranty period. It is also NOT the useful life of the tank.
The date printed on the tank is the point at which we recommend retesting the container at 5 bar to ensure it is safe to continue using as a pressure vessel.
This test must be performed with pressurised water. DO NOT USE GAS. Once this test is completed, the existing date can be removed with isopropyl alcohol and 2 years from the test date can be marked on the tank with permanent ink.
Unfortunately, we cannot guarantee the conditions under which the tank has been stored and used, as we cannot guarantee the safety of the tank for an extended period of time.
However, we do have some fermenters still in use that are over 5 years old and still working under pressure regularly. The King Fermentors you have are almost certainly still safe to use, but we cannot guarantee it.
The date is a safety precaution and designed to keep users aware that they are handling a pressurised tank and not to be careless with its handling. As these tanks have the capacity to hold up to 10 bar before breaking, there is potential for real danger if mishandled.
Translated from:
The date is NOT a warranty period. It is also NOT the usable lifespan of the tank.
The date printed on the tank is the point at which we recommend re-testing the vessel at 5 bar to ensure it is safe to continue using as a pressure vessel.
This test needs to be done using pressurised water. DO NOT USE GAS. Once this test has been completed, the existing date can be removed with isopropyl alcohol and 2 years from the date of test can be marked on the tank with permanent ink.
Unfortunately, we cannot guarantee the conditions which the tank has been stored in, used, or operated under, as such we cannot guarantee the safety of the tank for an extended period.
We do have, however, some fermenters that are still in use in use that are over 5 years old, and still working under pressure regularly. The FKJNR tanks you have are almost certainly still safe to use, however we cannot guarantee that.
The date is a safety precaution and designed to keep users aware that they are handling a pressure vessel and not to be blasé with its handling. As these tanks have the capability to hold up to 10 bar before rupturing, there is potential for real danger if they are mistreated severely.

