Air dryer system issues
We have a pressure-swing adsorption air dryer that is identical to the one shown here on the NMR wiki (Balston 75-20, currently a Parker-Balston 75-A20):
http://nmrwiki.org/wiki/index.php?title=NANUCairdrying_setup
The dryer feeds a receiver/ballast tank. Our system appears to produce properly dried air; however, at a certain point in the cycle (presumably the vent portion) the pressure in the receiver tank declines to a level unsuitable for use with our NMR. This occurs even if the outlet of the receiver tank is shut, suggesting that stored air is backing out through the air dryer.
We are struggling to find a manual/technical information for this air dryer to help troubleshoot our issues. It appears the issue could be resolved by a check valve placed at the tank input, although it seems unlikely that the dryer was designed to require such an element. Rather, it would seem that some internal element of the dryer (i.e. within the blue control box) is at fault--possibly the solenoid valve that controls venting/re-pressurization, or the assembly at the outlet (probably a shuttle valve with a bypass).
1) Assuming it exists, could someone possibly provide technical documentation for this air dryer?2) Do most systems have an element to prevent backflow from the receiver tank to the dryer, or should a properly functioning dryer prevent this?
Any more general thoughts or comments regarding our issue are welcome, as are clarifying questions. Thanks in advance for your assistance!
A few additional details:1) House air is being supplied to the drier at 7 bar (regulated).2) The receiver tank will build to about 7 bar until one of the dryer solenoid valves switches (venting air is audible); pressure then declines to a fairly stable 4 bar.
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