Compressor Filter Size - Compact or Standard?

[rossn]

I'm looking to purchase a filter for my compressor, and am looking primarily at Wilkerson/Dixon and Norgren.

Each mfg seems to make miniature, compact, standard, and (sometimes) jumbo sized bodies for their filters. My use of compressed air will generally be intermittent, and given I may mount them on the portable 7.4CFM@90 compressor, I'm leaning towards the compact models (Wilkerson=F18, Norgren=F73C) over the next (standard) size up.

Is there any reason I shouldn't consider these compact models over the standard models?

CFM seems pretty high on the compact models, but it is at 150psi, which is hard to interpret at 90psi. I'm also curious in general information about filter longevity and replacement costs in the compact size versus standard size.

 

[cvairwerks]

Simply look at the maximum flow rate and pressure, and flow rate and the pressures you need to run. As long as the FRL's is larger than what you need, you are ok.

Sizing needs to be based on flow rate, location and how much coin you are willing to drop on it. No need for a regulator that's running 1" ports to regulate a line for an air brush and conversely, running a 1/4 port unit for a system that will be running near max capacity won't cut it.

Pick a brand that has decent support and is within your price range. Some of the cheap stuff out there has no real product support and you can't get parts for them this month, let along a couple of years down the road.

We used to change filters about once a year, unless we got some big slugs of crud out of the system. I would advise keeping one element and a set of seals on hand so that you are not down for long, should you need to change the element our or have a seal start leaking.

 

[rossn]

Good points on product support, and good to know that even under heavy use the filters only get changed annually (that probably means I'll change them once a decade

I think it's a little different in that you have to look at the pressure drop to determine what is a reasonable pressure drop and what is not. Furthermore, flow rate seems to be a little more complicated than meets the eye... specifically, I don't think it should be based of the CFM of the compressor, rather the CFM that may get pulled by the tool, even if for a short period until the tank pressure drops. If not sized for that, then the pressure drop will be too great due to resistance in the system.

In these cases, it comes down to if I use the mini or compact units, and I'm inclined to think that I could see short bursts of 30-40CFM, meaning the compact (F73G or F18) units are probably a better fit.

My understanding is also that an oversize filter can actually decrease the performance due to the velocity of the air being too low. This gets trickier when thinking about a compressor being used for a spectrum of uses (nailer through small die grinder).

So, that's what I was trying to get to, though I'm still trying to confirm if I do F08/F72G vs F18/F73G.

 

[cvairwerks]

Unless you assemble the FRL stack backwards, the filter is before the regulator, so the drop across the elements is not a factor, unless you are regulating the pressure to within the drop limits of the filter and supply line. In that case, you are looking at the wrong size equipment. Until you get into stuff like some 3/4" and 1" impacts or blast equipment, you aren't going to see flow rates that high in the average garage shop, and a 1/4" line won't handle that for more than a couple of seconds anyway.

In Colorado, I doubt that there are going to be very many days in a year that you will see humidity high enough that the filter is going to be heavily taxed. I live where the humidity swings between 40 and 80% on average, and in running air drills and die grinders most of the time. I can count on one hand the number of times in the last year or two, that I had water in the tool exhaust, and I'm not running a filter on my compressor right now.
You didn't mention a blast cabinet, but that's a whole 'nuther rabbit hole.