What Information Do You Need for an Initial Filter Selection?
In a lot of industrial plants, filter selection still starts with phrases like “send me something similar to this” or “give me the cheapest option”. It may work once or twice, but over time this approach usually shows up as poor air or oil quality, higher energy consumption and recurring failures that nobody is really happy with.
For a reasonable initial filter selection, the first step is not the catalogue – it is having the right information about your system on the table. This article summarises, in practical terms, which data and parameters you should collect before choosing a filter: from fluid type, pressure and flow to contamination profile, downstream sensitivity and installation and maintenance constraints.
1. Basic information – what are we filtering, and for what purpose?
The first group of information is about the fluid and the application itself. Without this, no selection is truly reliable.
1.1 Fluid type
- Compressed air, gas, lubrication oil, hydraulic oil, cooling water, process fluid, etc.
- Approximate density and viscosity (if available or known from the fluid specification).
Fluid type drives the choice of media, housing material and seals, as well as the acceptable temperature and pressure ranges.
1.2 Filter location and role in the system
- Compressor inlet filter, line filter, pre-/post-dryer filter, point-of-use filter, return line oil filter, etc.
- Main purpose: protecting equipment (compressors, pumps, valves, instruments) or protecting product quality at the process / end user?
A filter that protects equipment focuses on preventing damage and downtime, while a filter linked to product quality must also respect customer or regulatory requirements.
1.3 Sensitivity of the downstream user
- General tools, simple actuators → medium sensitivity,
- Paint lines, final packaging, instrumentation → high sensitivity,
- Food, pharma, lab equipment → very high sensitivity.
The higher the sensitivity, the more carefully filtration class, number of stages and media type must be chosen.
2. Hydraulic and operating data – pressure, flow, temperature and pattern
The second group of information describes how the system actually runs. Many problems with pressure drop, rapid clogging and noise have their roots right here.
2.1 Operating and maximum pressure
- Normal operating pressure (for example 7 or 10 bar for compressed air),
- Maximum design pressure and any expected pressure spikes.
Pressure rating of the housing and connections must match these values; otherwise, long-term safety is compromised.
2.2 Average and peak flow
- Normal flow (Nm³/h, m³/min or L/min, depending on the fluid),
- Peak flow during high-demand periods,
- Operating pattern: continuous, shift-based, intermittent, load/unload, etc.
For correct sizing, peak flow is crucial. An undersized filter may work on paper but will drive up pressure drop and wear in real operation.
2.3 Fluid and ambient temperature
- Approximate minimum and maximum fluid temperature,
- Ambient temperature at the installation point and possible rapid changes,
- Presence of corrosive vapours or special conditions (outdoor installation, proximity to heat sources, etc.).
Temperature range is a key input for selecting the right media and seal materials and must be known at the initial selection stage.
3. Contamination profile and required quality level
Filters exist because of contamination, so it makes sense to have at least a basic picture of what you are trying to remove.
3.1 Dominant contamination type
- Solid particles (dust, wear particles, rust),
- Oil (droplets, oil aerosols, vapours),
- Moisture and condensate,
- A combination of the above.
This information points us towards the right type of filtration: particulate, coalescing, oil removal, adsorption, or a staged combination.
3.2 Approximate particle size and loading
- Are we dealing mainly with fine particles (micron and sub-micron) or coarser solids?
- Is contamination relatively stable, or do we see occasional shocks (for example after maintenance, start-up, or process upsets)?
You may not always have precise numbers, but even a qualitative description is very helpful when choosing filtration class and element type.
3.3 Standards and quality classes
- For compressed air: any required classes under standards such as ISO 8573 (if applicable),
- For other fluids: internal company specifications or customer requirements.
Knowing the target quality helps avoid both over-filtration (unnecessary cost and pressure drop) and under-filtration (quality and reliability issues).
4. Installation and maintenance constraints
The “best” filter on paper is not a good choice if it is difficult or unsafe to install and service in the real plant. Some important points to clarify early:
4.1 Connection type and line size
- Connection type: threaded, flanged, clamp, etc.,
- Nominal line size (e.g. ½", 2", DN50).
This avoids surprises during installation and reduces the need for extra reducers and adapters that increase complexity and pressure drop.
4.2 Space available for installation and element changes
- Usable height and width for opening the housing,
- Access direction (from above, below or from the side),
- Mechanical obstacles or structural elements nearby.
Understanding physical constraints helps you choose a filter that can actually be serviced easily in its real location.
4.3 Service schedule and available manpower
- Expected service interval (monthly, quarterly, based on running hours, etc.),
- Number of people and time typically available for inspections and replacements,
- Possibility of planned shutdowns versus need for quick, on-the-fly changes.
If element replacement is too complex and time-consuming, it tends to be delayed – and delayed replacements almost always show up as quality and reliability issues.
5. Additional information when you care about life-cycle cost
If you want your initial selection to be more than just “today’s lowest price”, it helps to also consider a few pieces of life-cycle cost information:
- Approximate cost of energy on site (especially for compressors and pumps),
- Cost of line stoppage or failure of sensitive downstream equipment,
- Past experience in the plant with specific filter brands or models,
- Supply constraints: lead times, local availability of spare elements.
With these data points, you can compare options not only by purchase price but also by the overall mix of quality, pressure drop, maintenance effort and long-term operating cost.
Once you have collected these basic parameters, turning them into a concrete product choice becomes much easier. You can, for example, review suitable filtration products in the PowerSep product range and share your system details with the technical team to narrow down the options for an appropriate initial filter selection.