It's probably my explanation, it is hard to make a technical description quickly.
I'm wondering if you're referring to the valve in the quick coupler on the LP hose, but that makes this puzzling:
Maybe it's just a matter of terminology? There are three valves all together, and none are identical to the schrader valve on a car tire. I probably wouldn't have thought of any of them as schrader valves, other than hearing so many references to BC's using schrader valves. I'd describe them as poppet valves (Schrader being a type of poppet valve), but whatever term is used all three are fairly similar as I understand them.
The Schrader valve (also called American valve) is a brand of pneumatic tire valve used on virtually every motor vehicle in the world today. The Schrader company, for which it was named, was founded in 1844 by August Schrader. The original Schrader valve design was patented in the United States in 1893.The Schrader valve consists of a valve stem into which a valve core is threaded, and is used on virtually all automobile tires and motorcycle tires and most wider rimmed bicycle tires. The valve core is a poppet valve assisted by a spring.
The Schrader valve is located in the inflator hose, and can be replaced by a tire tube valve. It is opened and stays open when connected to the BC, providing IP to the inflator valve.
There's the dump valve (clearly irrelevant to the discussion), the valve in the quick coupler, and the inflator valve. If the LP hose is connected and there hasn't been some kind of failure then the valve in the coupler will be open whether IP is correct, incorrect, or 0 psi as a result of an empty tank.
You are correct.
I was under the impression that the inflator valve is (at least similar to) a schrader valve. The only question is whether it opens upstream or downstream. The dump valve would also appear to be a schrader-like valve, though obviously larger than the standard tire valve. I haven't taken one apart, but the design certainly appears to open upstream against pressure in both cases. In that case too-high IP will close the inflator valve with more force rather than cause a free flow, which was the relevant point of my post.
The ones I have pulled apart open upstream and, in that way, act like Schrader valves. In that case too-high IP will close the inflator valve with more force rather than cause a free flow.
The quick coupler on every non-integrated BC I've seen appears to be similar to the one for my air tools. Though it doesn't apply to my equipment I'd be curious how the connector on an Air2 prevents airflow if it doesn't use a shrader valve or something that's quite similar.
Externally the Schrader connector looks like the air tool connector, but notice on the male connection there is a tab, which also would restrict airflow, that engages the Schrader valve in the female connector, except the Schrader valve restricts the air more. On an air tool male connection there is no restriction and as you look into the female connection there is no schrader valve mechanism, they use a different valve in order to pass more air that is necessary to run the tool. It is the same in function as a Schrader valve but is different in design and use, however this type of connector is used in Air 2 type applications because of the need for greater airflow.
Check out this manual for the inflator:
http://www.aqualung.com/militaryandprofessional/product_information/Powerline_DualValve_rev09_09.pdf
Bob
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There is no problem that can't be solved with a liberal application of sex, tequila, money, duct tape, or high explosives, not necessarily in that order.