Strainers vs. Filters

Key Differences in Particle Retention and Efficiency

Industrial filtration is the separation of solids from fluids (liquid or gas) to protect or improve a downstream process. Most applications clearly fall into either “coarse” (strainer) or “fine” (filter) categories, but there is a gray area of overlap. This article explains the practical differences and how to choose correctly.

 

Determine the Particle Size to Retain

Particle size is defined by your process and the equipment downstream. We typically recommend targeting particles that are 33% to 50% of the maximum allowable size. Multiple smaller particles can sometimes agglomerate into larger ones in low-velocity areas of the pipeline, so a finer target helps reduce that risk.

 

Also consider particle shape, deformability, and concentration. Choosing a finer retention increases housing and element complexity (and cost).

 

Straining or Filtering?

Pipeline strainers can be supplied with mesh-lined perforated screens as fine as 400 mesh (~38 microns). However, just because it is possible does not mean it is the best choice.

 

As a practical guideline:

• Strainers are best for particles you can see with the naked eye — generally larger than 50 microns.
• Filters become the preferred option for particles finer than about 150 microns, especially when higher efficiency is required.

Nominal vs Absolute Retention

All filtration ratings are considered nominal unless specifically stated as absolute. Nominal means approximate efficiency. Absolute typically means 99% or greater efficiency at the stated micron size.

 

This is one of the most misunderstood topics in industrial filtration. Overall efficiency depends on both the element design and how it seals inside the vessel.

Most pipeline strainer elements rely on a metal-to-metal seal and do not provide reliable sealing much finer than 100 mesh (~150 microns). If your process cannot tolerate particles finer than 100 mesh, a filter is the better choice.

 

Filter bags and cartridges use elastomeric or crush seals to prevent bypass. Nominal-rated media often relies on a particle “cake” to improve efficiency over time, while absolute-rated media maintains high efficiency from the start.

 

More detail is available in our Filtration Efficiency article.

 

Filtration Ratio and Element Design

The ratio of element surface area to pipe cross-sectional area is especially important in the 100–200 micron range where either a strainer or filter could be used.

Pipeline strainers typically use a perforated substrate with wire mesh welded to the surface. Particle accumulation is mostly limited to the surface of the element.

 

Filters (cartridges or bags) provide both surface and depth filtration. Multiple layers capture progressively finer particles, increasing both efficiency and solids-holding capacity.

 

If solids are normally very low and the device is only protecting against an upset condition, a pipeline strainer may still be acceptable even below 100 microns. When continuous particle removal is expected, or when even a few larger particles would cause problems downstream, the added complexity of a filter is usually justified.

 

Common Features of Strainers and Filters

Both can be supplied in duplex configurations so the process never has to stop for cleaning or element replacement. Both can also be automated for self-cleaning when personnel are not available or when differential pressure must be tightly controlled.

 

Information Needed for Proper Selection

To recommend the most cost-effective and reliable solution, we need:

1. Common fluid name
2. Particle size to remove
3. Estimated solids concentration (PPM)
4. Description of the solids
5. Maximum flow rate, pressure, and temperature
6. Inlet/outlet pipe size, connection type, and material
7. Whether the process can be interrupted for cleaning or element change-out
8. Overview of the application, the problem you are solving, and any special requirements (coatings, documentation, NDT, etc.)

9. Our product-specific inquiry forms are designed to capture exactly this information so we can prepare an accurate proposal.