3 questions “Funnel the Spec” to one product type.
Start at the top, follow the path down, end on the recommendation. Designed for distributors to send a customer ahead of a quote call.
Question 1
What contaminant is the customer actually targeting?
Liquid oil + water mist
Question 2a
Is the application audit-driven (Class 0 oil, food, pharma, breathing air)?
If No · general plant air
Recommend
Coalescing Filter
0.1 micron for general plant air, 0.01 micron for paint, instruments, or anything spec'd to Class 1 oil. Particulate pre-filter upstream is non-negotiable.
If Yes · audit-driven Class 0
Recommend
Activated Carbon Filter
Coalescing 0.01 micron + activated carbon in series. Carbon is the only media that captures gaseous oil vapor and gets the spec to Class 0.
Dry solids · pipe scale, rust, desiccant fines
Question 2b
Pre-filter upstream of coalescing, or after-filter downstream of a desiccant dryer?
If Pre-filter
Recommend
Particulate Filter (5 micron)
Cheap element protecting the more expensive coalescing downstream. Skipping it cuts coalescing element life from 12 months to 3.
If After-filter behind a desiccant dryer
Recommend
Particulate Filter (1 micron)
Catches the desiccant fines the bed sheds before they reach valves and air-bearing instruments. Mandatory on every desiccant install.
Specialty · medical / intake / inside the compressor
Question 2c
Which one — medical-air outlet, compressor inlet, or rotary-screw service?
If Medical-air outlet · NFPA 99
Recommend
Medical / Sterile Filter
Final stage of any hospital, surgery-center, dental, or dialysis medical-air train. Quote with CO/CO2 monitoring and the full upstream stack.
If Compressor intake · indoor near occupied space
Recommend
Intake Silencer / Filter-Silencer
Combines intake filtration and 10-15 dB acoustic attenuation in one housing. Default spec on any indoor commercial install near offices, exam rooms, or classrooms.
Two universal rules behind the tree: coalescing always installs upstream of any desiccant dryer (oil carryover ruins desiccant media fast), and activated carbon always installs downstream of coalescing (liquid oil saturates carbon in days). The rotary-screw air-oil separator isn't a stage in the customer's filter train — it lives inside the compressor package and gets quoted on the service-parts cross, not as part of a downstream build.
Filtration isn't a filter — it's a stack. Sell the stack and the customer hits their audit. Sell one element and they fail it.
SPC distributor playbook Filtration · how to spec the train