air-preparation

name	air-preparation
description	Compressed air preparation — filtration/regulation/lubrication (FRL), drying (refrigerant/desiccant), air quality ISO 8573-1, dew point, pressure drop, compressor selection, ISO 4414.
metadata	{"priority":7,"promptSignals":{"phrases":["air preparation","FRL unit","compressed air quality","air dryer","ISO 8573","desiccant dryer","refrigerant dryer"],"minScore":3}}

Compressed Air Preparation — Complete Skill

ISO 8573-1 Air Quality Classification

Three quality parameters:

Class	Particles (max)	Water (pressure dew point)	Oil (total)
1	0.1 μm; 0.1 mg/m³	-70°C	0.01 mg/m³
2	1 μm; 1 mg/m³	-40°C	0.1 mg/m³
3	5 μm; 5 mg/m³	-20°C	1 mg/m³
4	15 μm; 8 mg/m³	+3°C	5 mg/m³
5	40 μm; 10 mg/m³	+7°C	25 mg/m³

Notation: ISO 8573-1:2010 [solid:water:oil] e.g., Class 1.2.1

Application requirements:

Application	Typical class
Pneumatic cylinders (no lube)	3.4.3
Spray painting	1.2.1
Food contact	1.2.1
Air bearing	1.1.1
Instrument air	2.2.2
Breathable air	1.2.1 + CO check

Compressor Selection

Reciprocating (piston): Flow: 0.5–30 m³/min; Pressure: up to 40 bar; Pulsating flow → needs receiver tank Oil-lubricated or oil-free (for clean air applications)

Rotary screw: Flow: 0.5–500 m³/min; Pressure: 6–13 bar (single stage); most common industrial Oil-flooded (oil separator required downstream) or oil-free (no separator needed)

Centrifugal (turbo): Flow: > 100 m³/min; Pressure: 6–10 bar; oil-free; best for large industrial plants

Power estimation: P_comp = (m_dot × c_p × T_in / η_iso) × [(P_out/P_in)^((γ-1)/γ) - 1] [kW; c_p = 1.005 kJ/(kg·K); γ = 1.4 for air] η_iso = 0.65–0.80 (isentropic efficiency)

Receiver tank volume: V_tank = (Q_comp - Q_demand) × Δt / ΔP [m³; Q in m³/s at working pressure; ΔP = pressure band [Pa]] Minimum: V_tank ≥ 5–10 × Q_comp [L; Q in L/min] for pressure stabilization

Filtration

Coalescing filter: Removes liquid water and oil aerosols; 0.01–5 μm particle removal Efficiency: 99.999% at rated flow; replace element every 4000–8000 hr Pressure drop: 0.1–0.3 bar new; replace at > 0.5 bar

Particulate filter: Removes solid particles; 5–40 μm rating typical Pre-filter before coalescing; protects expensive downstream elements

Adsorption filter (activated carbon): Removes oil vapors; reduces oil to < 0.003 mg/m³ Place downstream of coalescing filter; limited capacity → replace regularly

Filter sizing: Use manufacturer flow curves; verify ΔP < 0.2 bar at max flow Size for 110–120% of nominal flow to extend element life

Drying

Refrigerant Dryer (most common)

Operation: cool air below dew point → condensate out; reheat to reduce downstream humidity Pressure dew point (PDP) achievable: +3°C to +10°C (ISO Class 4 or 5 moisture) Power: 0.5–5 kW (depends on flow) Limitations: cannot achieve PDP < +3°C; not suitable for outdoor or below-freezing conditions

PDP at system pressure: PDP_at_P = PDP_at_1bar + ΔT_correction [ΔT = 15°C per bar increase approximately] At 7 bar: if dryer gives +3°C PDP, actual PDP at line ≈ +3°C (dryer already accounts for pressure)

Desiccant Dryer (heatless or heated)

Heatless (PSA): two towers with activated alumina or molecular sieves; one drying, one regenerating Purge air: 15–20% of inlet flow used to regenerate (net output = 80–85% of inlet) PDP achievable: -20°C to -70°C (ISO Class 2 or 1) Cycle time: typically 5–10 min per tower

Heated desiccant (HOC — heat of compression): uses compressor heat for regeneration; zero purge air loss; energy efficient

Desiccant life: 2–5 years (activated alumina); replace when PDP rises 5°C above spec

PDP calculation (desiccant): PDP_required = lowest ambient operating T - 10°C safety margin [e.g., outdoor at -20°C → PDP = -30°C → Class 2]

Pressure Regulation

Pressure regulator: Set at 10% below system minimum required pressure (to account for line pressure drop) Select Cv for ΔP at maximum flow: Q = Cv × √(ΔP/SG) [Q in US gal/min; SG = 1 for air]

System pressure drop budget: Filter: 0.1–0.3 bar; dryer: 0.1–0.2 bar; regulator: 0.2–0.5 bar; piping + fittings: 0.2–0.5 bar Total: allow 1.0–1.5 bar pressure drop from compressor to point of use

Example: System requires 6 bar at tools; losses 1.2 bar → set compressor to 7.5–8 bar

Lubrication (FRL — Filter/Regulator/Lubricator)

For lubricated pneumatic tools only: Oil mist injected into air stream; flow-dependent injection Setting: 1 drop/min per 10 L/min flow (typical starting point)

When NOT to lubricate: Servo valves; air bearings; food/pharma; any instrument that will be damaged by oil Modern pneumatic cylinders (ISO 15552) often rated for unlubricated service

Piping and Distribution

Velocity limits: Mains: 6–9 m/s; branches: 3–6 m/s; drops: 1–3 m/s

Pipe diameter (simplified): D = √(Q_max × L / (490 × ΔP_allowed)) [mm; Q in m³/hr; L in m; ΔP in bar] Use ring main (loop) topology to reduce pressure drop and allow bidirectional flow

Slope: pipe pitched 1:200 toward drain points (condensate removal) Isolation valves: every 30–50 m for maintenance; quick-connects at point of use

Standards

Standard	Scope
ISO 8573-1	Air quality classes
ISO 8573-2	Particle measurement
ISO 4414	Pneumatic fluid power safety
CAGI/Compressed Air Challenge	Best practices for energy efficiency

Output

Provide: ISO 8573-1 air quality class required [solid.water.oil], pressure dew point [°C], compressor type and delivery pressure [bar], flow rate [m³/min], receiver tank volume [L], filtration stages (particulate → coalescing → activated carbon), dryer type (refrigerant/desiccant) and achievable PDP [°C], regulator set pressure [bar], system pressure drop budget [bar], pipe sizing [mm], and applicable standard (ISO 8573-1, ISO 4414).