It's gutter all the way up to the stars.
There I am, innocently* looking on Amazon for vacuum relief valves - the equivalent of overpressure failsafes, only underpressure - and I find one that perfectly fits my specs, amazingly. Only one, though. So I search manufacturer's name and product designation for vacuum relief to see if there are any competitors: "Control Devices VR".
Well.
*Gosh* but there's a lot of computer-assisted mind control smut out there. o.O
*'innocently'. Eeyup. Heh.