FYI - The Solberg intake filter cans are the same size whether you order the large or the small... I know because I mistakenly ordered the large one first. It required an adaptor and kept vibrating loose. The smaller 1/4" model fits directly into the RIX SA3 port. The cans are the same size and take the same #07 filter. I think its the size if the intake hole in the compressor that dictates the flow rate capacity of these filters.
We can reply in two parts I hope.
First are you sure about 1/4" it's proberbly a typo as the air intake fitting on the SA-3 is 3/8" NPT female not 1/4".
The only 1/4" NPT ports on the 1st stage head is on the discharge side and for the relief valve.
I will look up the Solberg can numbers (and filter number) later suitable for the SA-3 at 3 ACFM flow but it is not a direct fit into the 1st stage head. Again from memory if a Solburg is used it's bigger both taller and wider and has a 3/4" male thread and intake hole. Hence you need to reduce down with a PTR adaptor, a brass fitting 3/4" female one end and 3/8" NPT male the other. Also as the 1/2" threaded Solberg thread limits out for a 2.2 SCFM flow with the paper element from the design point we have to calculate for all options.
I also note that the Rix Mil Spec filter is much better but I appreciate too expensive for you guys hence my explanations but you all need also appreciate that this information is more from the "Custom Shop" end of the compressor build and that these parts are not available from Rix so while there may be alternative we need also to understand the complex application.
Having said that I would proberbly also settle for a 1/2" thread reduce to 2.2 SCFM and split the difference.
Now if you really whant to see the difference. Measure the head temperature with an infrared gun as see the difference the increased port size makes going from 3/8" to 3/4" . Also test with and without the polyester and the paper filter as it makes my point way better than I can describe in text.
Also consider that using the 10Mu polyester filter is much better for ease of flow for a given cross section area of filter than the same size 2Mu paper element but the finer 2Mu paper element attracts more particulate and for example parking the thing in your garage with the air intake under a tree will result in burnt sap and pollen cooked onto the discharge side of the discharge valve over very little time using polyester but be clean as a whistle using paper.
I know your not pumping nitrox so I cant pull a safety warning but these are application aspects not covered in the manual or at the factory at the customer level.
If an extension hose is used as per the yellow "Gas Bag" reclaim pump in the photo then its a 3/4" OD by 1/2" ID food grade non off gassing hose. The other material we use is called Tygon Tubing.
For pulsation dampening and pressure drop problems using too long a hose length is another problem. 10 foot is the maximum length for the 1/2" bore intake hose at 3 SCFM and the "penalty" can again be demonstrated by the infrared gun test.
Lowering the RPM and flow from 3.0 SCFM to 2.2 SCFM also shows some clear benifit.
But making the minimum of presure restriction at the intake side of the pump is critical.
Even more in hot climates, the Dessert Chiller version of the miltary SA-6 has a monster Air intake filter, granted more for the reasons on fine dust clogging all and sundry
Compared with a SA-6 Navy Built for the navy applications in clean air at sea.
But you raise an important aspect of the compressor design that maybe needs a better fuller explanation than I have given so far but I hope we all get the drift. Iain