youare mixixng references. it will always be 100% RH hitting the filters. if the environment is30% RH you may or may not get much if anything form the first separator. once the RH hits 100 it goes no higher. You saying that the filter is .7% may be true so long as you reference the gas to 1 ata and not the 150 bar it is under in reality. for sake of argument all RH's are reference to what you are going to breath not what is in the tank. your tank may have 80% RH in it at 200 bar. as bar drops so does the RH because as the Bar drops the gas is capable of holding more.So you are saying the article is wrong.
The article states, by example, that the amount of water in the air reaching the filter stack is relative (0.7%) to the water in air at the intake of the compressor. You are saying this is not true.
Until some one educates me difrferently there is but 2 reasonss to have the BPR or PMV as you called it is this.
1. to prpovide a back presure such that the force on the final piston equals teh force of hte other cylendars. that keeps it runn8ing vibration smooth instead of like a tire on your car that threw a weight.
2. It provides a back pressure on the final moisture separator so that it constantly is under say 140 bar when the tank is only under 50 bar. the higher the back pressure the more moisture is removed. ( relate to squeezing a SPONG) With out it you would try to remove water with 20 bar and then 50 bar etc going higher as tHE tank fills resulting in higher Moisture content in the tank THAN IF TEH SEPARATOR WAS SALWAYS at 140 bar untill the tank got 141 bar. 140 bar as I have read ; purges 99+ percent of the water. That should perhaps be volumn but that translates to RH also when decompressed through the regulator. With out the filter stack you would be breathing perhaps 1/5% RH at 1 ata. The desicant is what removes additional water that the mechanical separator can not do. You can help out the situation by cooling the final stage temp using a heat exchanger or 50 ft of hp pipe coil in a water bath befor hitting the final water separator. lowering the temp raises RH and causes more water to come out. You have 3 factrors --------- RH temp Pressure----------. RH become moot once teh gas first hits 100%. lower temp get out more water .., raise pressure get out more water.
The next phase in getting dry air is to have a large volume filter canister. the larger the canister the longer the gas is in fie filter stack. the longer time the more it filters. It is called dwell time. you can calaulate it by saying what is the cuft of the filter at psi and divide it by your compressor output. so I have a say 4 inch 3 ft filter can. it ( for arguments sake) at psi is 30 cuft. my compressor pumps 5 cuft. dwell time is 6 minutes. that dwell time is controlled by the back pressure onthe filter output just like teh compressor moisture is dependent on the PMV. You put a PMV on the final output of the filter stack for best air.