Filter Performance Metrics

Beta ratio (β)

β at particle size x(c) = upstream particle count ÷ downstream particle count at ≥x µm. Efficiency = (1 − 1/β) × 100%. β₁₀(c) = 200 → 99.5% efficiency. β₁₀(c) = 75 → 98.7%. Measured per ISO 16889 with ISO 11171 calibrated counter. Always requires the "(c)" suffix for valid comparison.

Dirt holding capacity (DHC)

Total grams of standardized test contaminant captured by the filter from initial restriction to terminal restriction. Measured per ISO 16889 (fluid filters) and ISO 5011 (air filters). DHC determines service interval — the element reaches the service threshold when DHC is exhausted at the application ingress rate.

Initial differential pressure

Pressure drop across a clean element at rated flow and fluid viscosity. Lower initial ΔP means more available headroom before the service limit. Initial ΔP is higher for finer media (better Beta) and decreases with increasing media area (higher DHC). There is a fundamental efficiency-capacity-restriction tradeoff in media design.

Collapse pressure

Maximum differential pressure an element withstands without structural failure (media collapse, end-cap separation, or center tube buckling). Must exceed maximum possible system ΔP — bypass valve cracking pressure during cold start with high-viscosity oil. Minimum collapse rating: 2× maximum bypass valve opening pressure.

Fractional efficiency

Efficiency measured separately at multiple particle size ranges (0.5, 1, 2, 3, 5, 7, 10, 20, 40, 80 µm in ISO 5011) to characterize the complete efficiency curve. A filter may have high efficiency at ≥10 µm but poor efficiency at 2–5 µm — the critical wear range. Fractional efficiency reveals which particle sizes are not being controlled.

β₁₀(c) = 75[ISO 16889]

98.7% efficiency

β₁₀(c) = 200[ISO 16889]

99.5% efficiency

β₁₀(c) = 1000[ISO 16889]

99.9% efficiency

Synthetic DHC vs cellulose

2–4× at equivalent efficiency

MACROCORE™ DHC advantage[ISO 5011]

Up to 2× cellulose

Minimum collapse pressure

2× bypass valve opening pressure