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Pore size refers to the diameter of the openings or passages in the porous structure of a metal sintered filter. Because sintered metal filters are made by bonding metal powder or mesh layers under high heat, the resulting pore structure is three‑dimensional and tortuous—not simple straight holes like a drilled plate.
Two terms are commonly used:
Nominal pore size – The pore size at which the filter captures a stated percentage of particles (e.g., 98% at 10 µm). Useful for non‑critical applications.
Absolute pore size – The pore size at which the filter captures 99.9 % or more of particles of that size or larger. Required for critical systems such as servo hydraulics, pharmaceutical processes, or aerospace fuel systems.
For most industrial applications, absolute pore size is the safer, more reliable specification.
Choosing the wrong pore size affects every aspect of filter performance:
| If pore size is too fine | If pore size is too coarse |
|---|---|
| High initial pressure drop | Contaminants pass through |
| Rapid clogging | Downstream components wear out faster |
| Frequent cleaning or replacement | Fluid cleanliness targets not met |
| Higher energy costs | System reliability reduced |
The goal is to select the largest pore size that reliably captures the contaminants you need to remove. This gives you the longest service life and lowest pressure drop while still protecting your equipment.
Before selecting a pore size, analyze the contaminant you need to remove:
What is the particle size distribution? Obtain a sample or use historical fluid analysis. If most particles are 10 µm and larger, a 10 µm absolute filter will work. If there is a significant fraction at 5 µm, you might need a 5 µm rating.
What is the particle shape? Sharp, angular particles are easier to capture than spherical ones. Soft, deformable particles (like gels or rubber) may require finer filters than their nominal size suggests.
What is the contaminant load? High loads need more dirt‑holding capacity. A coarser filter with larger pores can hold more contaminant before clogging.
Pro tip: If you don’t have detailed particle data, look at the component sensitivity. Servo valves often require 3–5 µm absolute; standard hydraulic pumps can tolerate 10–20 µm; gearboxes and bearings may be fine with 25–40 µm.
Different hydraulic and lubrication components have different tolerances to particle contamination. Use these general guidelines:
| Component Type | Recommended Absolute Pore Size (µm) |
|---|---|
| Servo valves, proportional valves | 3 – 5 |
| High‑pressure piston pumps | 5 – 10 |
| Vane pumps, gear pumps | 10 – 15 |
| Directional control valves | 10 – 20 |
| Rolling element bearings | 10 – 15 |
| Journal bearings, gears | 20 – 40 |
| Turbine lube oil systems | 10 – 20 |
| Fuel injection systems | 5 – 10 |
These are starting points. Always check your equipment manufacturer’s recommended cleanliness code and select a filter pore size capable of achieving that code.
Finer pore size increases resistance to flow. A metal sintered filter with 3 µm absolute pores will have a significantly higher clean pressure drop than a 20 µm filter of the same dimensions.
Calculate your acceptable pressure drop – For most hydraulic systems, a clean pressure drop of 0.5–2 bar (7–30 psi) is acceptable. Higher pressure drops waste energy and may open the bypass valve prematurely.
Check the filter’s rated flow – The manufacturer provides flow vs. pressure drop curves for each pore size. Use these to confirm the element can handle your system’s flow rate at an acceptable ΔP.
If your system requires high flow and fine filtration, consider using a larger filter housing or a sintered filter with more surface area (longer length or larger diameter) to reduce face velocity and pressure drop.
One of the main advantages of metal sintered filters is that they can be cleaned and reused. However, cleanability is affected by pore size:
Coarser pores (20–100 µm) – Easier to clean via backflushing or ultrasonic cleaning. Particles are less likely to become deeply embedded.
Finer pores (1–10 µm) – More difficult to clean. Particles can lodge deep in the tortuous pore structure. Ultrasonic cleaning or thermal burning is often required.
If you plan to reuse the filter many times, a slightly coarser pore size that still meets your cleanliness requirement will make cleaning easier and prolong total life.
Sintered metal filters derive strength from the interparticle bonds at the pore walls. As pore size decreases for a given material and thickness, the “solid to void” ratio increases; finer filters are actually stronger per unit thickness because there is more metal.
Conversely, a very coarse sintered powder filter (e.g., >100 µm) may have lower burst strength and be more susceptible to damage from pressure spikes. For high‑pressure applications, always consult the manufacturer’s pressure rating for the specific pore size.
For critical applications, do not rely solely on calculations. Perform a bubble point test (for absolute-rated filters) to verify that the actual pore size matches the specification.
If you are replacing an existing filter, the safest starting point is the OEM’s specified pore size. Then monitor pressure drop and fluid cleanliness to see if a coarser or finer rating would work better.
| Absolute Pore Size (µm) | Typical Applications |
|---|---|
| 1 – 3 | Ultra‑clean hydraulics (servo valves, aerospace), pharmaceutical filtration, ultrapure water |
| 5 – 10 | High‑pressure piston pumps, precision industrial hydraulics, turbine EHC systems |
| 15 – 25 | Standard industrial hydraulics, mobile equipment, lubrication circuits |
| 40 – 70 | Return line filters, coarse pre‑filters, fuel filtration |
| 100 – 200 | Pump inlet strainers, coarse separation, catalyst recovery |
Selecting the correct pore size for your porous metal filter or sintered filter requires balancing equipment sensitivity, contaminant characteristics, flow requirements, and operating conditions. Start with the component manufacturer’s recommendations, then use the guidelines above to refine your choice.
Selecting the right pore size is only half the battle. You also need a manufacturer who can deliver a metal sintered filter that meets your exact specifications – consistently, reliably, and at a fair price. That is where Huahang Filter comes in.
1. A full range of pore sizes
We manufacture sintered filters with absolute pore ratings from 1 µm to 200 µm, using 316L stainless steel as standard, plus 304, 310s, Hastelloy, Inconel, and Titanium for extreme environments. Whether you need a fine 3 µm absolute element for servo valves or a coarse 100 µm strainer for pump inlets, we deliver.
2. Multiple construction technologies
3. Custom pore size and dimensions
Your application may demand a non‑standard pore rating or unusual shape. We produce custom sintered filter discs, cartridges, sheets, cones, and complex geometries to your exact drawings or sample.
4. Engineering support for pore size selection
Not sure whether you need a 5 µm or 10 µm absolute rating? Our technical team will review your fluid analysis, component sensitivity, and operating conditions.
6. Reusable and sustainable
Many of our sintered stainless steel filters are designed for backwashing, ultrasonic cleaning, or thermal regeneration. One filter can last for years, dramatically reducing consumable costs and environmental waste.
