Gas fittings - end cap

[richc]

I've got a CO2 tank with a simple regulator that seems to be measuring input pressure. I want to connect this to a 3 way secondary regulator. The secondary regulator has a 4th output that connects directly to the input, I think I need to be able to seal this output as I have no way of knowing what the pressure is. All the outputs have threads that fit the conventional John Guest connectors.
Can anyone give me any advice on what part to use to cap this output?

Thanks

 

[Sean_Mc]

I guess you could use an isolation valve, maybe a better option on Harmony hut