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Old 08-19-2012, 12:04 PM   #14
Beastly Adventurer
Joined: Jul 2008
Location: The great state of confusion
Oddometer: 4,312

I was told that the valve was not supposed to "vent" until a certain threshold value was exceeded on EITHER side of "atmospheric" pressure -- both to the high side (some number of psi above zero-psi-gauge pressure) and to the low side some number of psi/inches of mercury below zero-psi-gauge pressure (i.e. a vacuum).

In other words there is a range of pressures above and below atmospheric at which the check valve does nothing and "holds" whatever pressure (positive or negative) that is sees in the tank.
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