KLC Pocket Filter F7 F8 F9: Performance Data, Pressure Drop Curves, and HVAC Application Guide

May 28, 2026

Pocket filters (also known as bag filters) are the workhorses of medium-efficiency HVAC filtration. Available in F7, F8, and F9 grades (ISO 16890 ePM1 to ePM2.5), these filters provide high dust-holding capacity and low initial resistance, making them ideal as secondary filters for AHUs and cleanroom pre-filtration. At KLC International, our pocket filters are engineered using high-strength synthetic fiber or fiberglass media to ensure structural integrity even under high airflow conditions.

Technical Performance Data (Standard 592x592mm)

Parameter	F7 (ePM1 50-65%)	F8 (ePM1 70-85%)	F9 (ePM1 >80%)
Initial Resistance	60 – 80 Pa	80 – 110 Pa	110 – 150 Pa
Final Resistance (Rec.)	250 Pa	300 Pa	450 Pa
Number of Pockets	6 – 8	6 – 10	8 – 12
Typical Airflow	3400 m³/h	3400 m³/h	3400 m³/h
Pocket Depth	380mm – 600mm	380mm – 600mm	500mm – 600mm

Understanding the Pressure Drop Curve

The performance of a pocket filter is defined by its Pressure Drop vs. Dust Loading curve.

Initial Phase: The filter has very low resistance, allowing for maximum energy efficiency.
Dust Loading: As the pockets capture particles, the "V-shape" design allows for a massive surface area, meaning the pressure rises much slower than with flat panel filters.
Replacement Point: When the pressure drop reaches the recommended final resistance (e.g., 250 Pa for F7), the filter must be replaced to prevent fan strain and bypass.

Why KLC Pocket Filters?

1. Sonic Welded Edges: Our synthetic pockets are ultrasonically welded to eliminate needle holes and prevent air bypass.

2. Internal Spacers: We use internal stay-bars to ensure each pocket opens fully, maximizing the effective filtration area.

3. Rigid Header Frame: Available in galvanized steel, plastic, or aluminum (20mm or 25mm) for easy installation in any AHU brand.

FAQ: Frequently Asked Questions

1. What is the difference between F7, F8, and F9 filters?
The difference is efficiency. F7 captures approx. 50-65% of PM1 particles; F8 captures 70-85%; F9 captures >80%. F9 provides the highest air purity but with higher resistance.

2. How often should pocket filters be replaced?
Typically every 3-6 months. However, it is best to monitor the pressure drop; replace them once they reach their rated final resistance.

3. What is a synthetic fiber pocket filter?
It is a filter made of layered synthetic media that is break-resistant and moisture-resistant, unlike traditional fiberglass.

4. Can I wash and reuse a pocket filter?
No. Pocket filters are disposable. Washing them will damage the fine fiber structure and destroy the filtration efficiency.

5. Why are there different numbers of pockets?
More pockets provide more surface area, which leads to lower initial resistance and a longer lifespan, but increases the purchase cost.

6. Do I need a pre-filter before the pocket filter?
Yes. Using a G3 or G4 panel filter as a pre-filter will protect the pocket filter from large dust, extending its life significantly.

7. Are KLC pocket filters ISO 16890 compliant?
Yes. All our HVAC filters are tested against ISO 16890 and EN 779:2012 standards.

8. What is the "V-shape" design for?
The V-shape ensures even airflow throughout the depth of the pocket, preventing the "clapping" of pockets and ensuring full utilization of the media.

Maximize your AHU performance.
View KLC Pocket Filter Specifications or Request a Pressure Drop Chart.