I agree with the check valve before the filter but don't understand your reasoning to have the moisture indicator before the filter. I use the moisture indicator to tell me when I should be replacing the filter.
I agree but am a tad confused with this thread the way its going. Its very far away for a optimal Rix SA-6 build
The reason for having two visual indicators on a SA-6 is
A. When two filter towers are used or
B. When a diesel or petrol engine drive is used.
The first visual indicator is fitted with a 20/40/60% indicator card and is fitted after the first molecular sieve tower in between filters 1 and filters 2. The second visual indicator is fitted with a 10/20/30% relative humidity card fitted downstream (after) the second filter tower. A non return valve can also also be fitted between the two filters in addition to the one fitted at the inlet side of filter 1. In addition a 2Mu in line particulate filter is also fitted after the second tower
Filter 1. Contains Activated Alumina as the first contact chemical from the separators at 20% by volume the balance being 13X molecular sieve.
Filter 2. Contains first 13x again 20% by volume as the first contact chemical, then Hopkalite for CO removal, then a balance "plug" of 13x again 20% by volume the balance filter being Molecular Sieve 13x
Two (2) 7Mu x 6mm thick minimum polyester filter pads are used to separate the chemicals in both towers.
The chemical in filter one is changed when the 20/40/60 reaches the 20 to 40 mark for ease of use.
Alternativly using a 10/20/30 in the first tower is OK but its very hard to see the 10 to 20 change due to the sensitivity of the indicator card
For an electric drive a single tower would be used with 13X only if using retail throw away cartridges
or a mix of 20% Activated Alumia and 13x if using a self fill re pack cartridge.
The height of the tower would be dependant on the required filter chemical life expectancy.
This would also depend on the indended operational cycles of the compressor and use it would also be calculated at requiring around 3 to 4 filter changes a year to ensure attention to purity and avoid long lags between use.
Adsorbsion is a complex subject with breathing gases, one reason why I'm so interested why many of the oil lubricated air compressor experts on the forum seem to make it such a simple undertaking.