How to Charge a Nitrox With M26

The M26 valve thread is a standard that was introduced by European Union regulations to differentiate between the valves on an air tank and the valve on a tank containing more than 22 percent oxygen (air contains 21 percent). The M26 valve thread has a different diameter than the thread used on a regulation DIN valve that is normally found on European scuba tanks. Filling a Nitrox tank fitted with an M26 valve means that a matching compressor regulator must be used to fill the tank.

Instructions

    • 1

      Perform a safety check of the cylinder. Check the hydrostatic test date stamped on the tank neck to check that it is within hydrostatic test dates. Ensure that the tank has markings that show it is safe to be filled with Nitrox. This typically is a green-and-yellow sticker marked "Nitrox" wrapped around the middle of the tank. Make sure that the tank's visual inspection date is current.

    • 2

      Check the working pressure of the cylinder marked on the tank neck. Set the air compressor controls to shut down when this pressure has been reached.

    • 3

      Place the cylinder in a water cooling tank.

    • 4

      Close the bleed valve. Attach an M26 valve from an oxygen cylinder to the tank valve. Open the valves and partially fill the cylinder to the desired nitrox mix. Normal air has 21 percent oxygen, so if you want a 32 percent mix, fill the cylinder to 11 percent by using the gauge to monitor the fill progress.

    • 5

      Turn off the valves. Disconnect the scuba cylinder. Attach the cylinder valve to a M26 valve from the air compressor. Fill the cylinder the rest of the way with ordinary air.

    • 6

      Analyze the mix and complete the fill logsheet.