[Hansfragger]

Originally Posted by Sunwong

Then, correct me If I am wrong, but there are no quick disconnect couplings that support 1/2''' internal flow.

This is unacceptable for me, I'm afraid. Why use 1/2''ID tubing and components if I am going to restrict the whole circuit to 3/8'' ?

I will be looking for an alternative but I am not very optimistic....

2) Colder products FL series. http://www.colder.com/asp_main/flfbind.asp . These are the highest flow, lowest pressure drop, valved couplings offered I have been able to find. These are beautiful, machined aluminum. You can order them with valves in both sides of the coupling. Downsides are weight, $$$$$$$$$!!!, and these are the only couplings of the group that are not manufactured in panel mount. When I spoke with Colder they were willing to manufacture a run of them in panel mount if the quantity were high enough, or a proposal could be submitted to them to add this configuration to their catalog.
I believe these are 1/2" or larger internal flow. Colder claimed that these are as good as it gets. Remember that ANY type of a quick release valved fitting is going to have some restriction. If you want the least amount of restriction possible, get the quick release fittings without the valves, or at least less valves. Instead of setting up your system the way you explained with 8 valves, drop down to 4 or 2 valves as each valve adds resistance. You have 2 other options:

1) The gas valves(also as bigben2k so gratiously added come in pvc) use a ball valve which would have zero practical resistance to flow when open, and as I measured, .472 ID.

2) You can take a PCI plate and modify it to accept 1/2" barbs with no restriction, but no valves also. This is the most compact setup (see enclosed photos) I didn't realize until Bio-Hazard so hilariously pointed out, the NSH fittings are "monsters"