10 inputs determine the right filtration.

A distributor-facing pre-quote checklist. If the customer answers most of these at the first call, the second call is the quote.

1. 01
   What ISO 8573-1 cleanliness class does the application actually need?

   The class determines the stack. Class 1 oil (liquid only) = 0.01 micron coalescing. Class 0 oil (liquid + vapor) = coalescing + carbon in series. Sterile-grade = full medical or pharma stack with sterile filter at the end. Customers who say "oil-free air" without citing a class usually mean Class 1 — confirm before quoting.
2. 02
   What's the system SCFM and operating pressure?

   Sizes every housing in the train. Oversize is fine (lower pressure drop, longer element life); undersize is the consistent failure mode — elements blind early, pressure drop spikes, downstream tools starve. Verify pressure rating against actual system pressure including any boosters.
3. 03
   What's the upstream filtration today — and what's the current element-replacement cadence?

   Coalescing elements lasting 3 months instead of 12 means the particulate pre-filter is missing or undersized. Walk the existing train before quoting; the right fix is usually adding the missing pre-stage, not replacing the symptom-stage with a premium brand.
4. 04
   Is there a regenerative desiccant dryer anywhere in the system?

   Desiccant beds shed fines into the downstream air — a particulate after-filter (1 micron) immediately downstream of every desiccant install is mandatory. Refrigerated dryers don't shed; refrigerated installs only need pre-filtration, not after-filtration.
5. 05
   Is the system feeding a medical-air outlet under NFPA 99?

   Different product, different code, different validation. Medical-air requires a sterile filter + CO/CO2 monitoring + alarm panel + dedicated medical-air compressor. NFPA 99 installs are inspection-driven — the documentation matters as much as the hardware.
6. 06
   Is the compressor indoors, near occupied space — offices, exam rooms, classrooms above or adjacent?

   That's the qualifier for a filter-silencer at the intake. Bare intake filters on a piston compressor in a mechanical room routinely test at 95-100 dBA at three feet — past the OSHA hearing-conservation action level. A filter-silencer knocks 10-15 dB off the intake contribution at the source.
7. 07
   What's the compressor brand/model/HP and when was the air/oil separator last replaced?

   For rotary-screw fleets, the separator is the anchor of the annual service kit. Cross-reference to KELTEC is typically 40-60% of OEM list pricing with same-day delivery. Bundle separator + oil filter + intake filter + oil onto one PM visit.
8. 08
   Does the customer have a differential-pressure gauge across each filter housing?

   DP is the only honest indicator for element replacement on every stage except carbon. Replace at 8-10 PSI DP, not on calendar guess. Retrofit DP gauges to existing housings as a paid service for customers running calendar replacement.
9. 09
   Where does the filter-sump condensate discharge — floor drain, sewer, or oil-water separator?

   Oil-bearing condensate to sanitary sewer is a regulatory violation in most jurisdictions ($25K-50K/day EPA fines). Every filter housing collecting liquid needs an automatic drain routed to an OWS, OWS effluent to permitted discharge.
10. 10
    Is the install indoor heated, or outdoor / unheated mechanical room?

    Outdoor or freezing installs need heated housings or insulated enclosures — water in the sump turns to ice, blocks the drain, and over-pressures the housing. Outdoor coalescing without freeze protection ruptures during the first cold snap.