How to Read Scuba Tanks - Hydro Stamps

How to Read Scuba Tanks - Hydro Stamps

Posted by Dive Professional: Will Taylor on on Mar 27th 2023

If it has been five years since your last thorough inspection, federal law now requires you to have your air tank tested. In the US, the Department of Transportation regulates this, while other countries have their own rules for pressurized vessel maintenance, use, and transportation. Due to the risks associated with pressurized air cylinders, regulations are similar across the board. A hydrostatic test is used to address these risks and locate any flaws that could put a diver in danger.

How to check for Hydro:

It is important for any diver to be able to read the stamping on any tank. Even if you are renting, always check the stamping as a safety precaution. Around the top of every tank, you can find vital specifications stamped. Keep in mind that the location and arrangement may differ depending on the manufacturer. Through practice, you'll be able to identify important specifications and understand their meaning.

To ensure safety, every cylinder is required to undergo a hydrostatic test once every five years. When a cylinder passes inspection, the test date is permanently stamped on it. In the given example, the test was conducted in March of 2023. An added "+" symbol after the test date indicates that the cylinder can be filled up to 10% higher than its maximum service pressure. As this test is conducted every five years, the cylinder may have multiple hydro dates stamped on it.

During a hydrostatic test, a technician looks for leaks in the tank, filling it with water and submerging it into a sealed chamber. The tank is pressurized to 5/3 of its normal pressure, causing it to inflate and displace water from the chamber into a burette. The amount of water displaced during pressurization is recorded, and the tank is held at this pressure for 30 seconds. The water is then returned to the chamber, but not all of it, as the tank has stretched slightly even though the pressure has been released. The amount the tank has stretched is called permanent expansion, and the difference between total and permanent expansion is elastic expansion. If the elastic expansion exceeds the limits set for your cylinder, it will be marked as condemned or with Xs over the DOT specifications. If the tank passes the hydrostatic testing, it will be stamped with the date and ID number of the shop that carried out the testing.

Public safety is the reason hydrostatic testing is mandated and regulated on such a high level. While Scuba tanks are made of durable metals, there are inherent dangers in dealing with highly pressurized gasses within a metal container. Compromised tanks can cause trouble underwater or injury if dropped or torn, causing the gas to propel the tank around a room. These tests not only keep people safe, but they keep people alive.

We are a scuba tank drop off point for Hydro and Tumble. We do visual inspections in-house.

If you have any questions call us at (310) 398-5759 one of our pros will be happy to help you out.