Actually, Ive got two regulators, both have four ports other than the inlet. The four ports are:

1. LP Outlet (Pushfit adapter)
2. Low pressure gauge (0-15 bar)
3. High pressure gauge (0-400 bar) on one regulator, blanking plug on the other
4. Looks like a relief valve of some sort, its a small fitting with a spring visible inside - on both regulators. These are much smaller than the Technobots 1000psi regulators, though.

Now that youve made me think about it, the High pressure gauge must be attached to the HP inlet. Is it acceptable just to screw the relief valve into that?