What is the Red plastic dust cap fitted in the big brass valve on the tank?

Within the black aluminium airbox, as fitted to our GAS IT tanks, you will see a red plastic cap that's stuck in a brass valve in the tank.

This red plastic cap is a dust cap in the pressure relief valve ( PRV ) and the red cap is designed to protect the valve from dirt and dust and is not to be removed from the pressure relief valve.

No extra pipes or fittings are needed to be screwed into the PRV.

All gas bottles, like exchange bottles and gas tanks have a PRV of some sort as it controls the safe release of gas pressure in the event of a fire