Filters for equipment
These are not filters on a shop duct but inside the machines themselves: hydraulic power units, compressors, diesel gensets, gearboxes and lubrication systems. They are rarely written into a project as a separate line, yet they decide whether a pump or a bearing survives to its scheduled overhaul. The consumable costs orders of magnitude less than the assembly it protects.
Every filtration point inside the machine
- Hydraulics: suction, pressure, return, off-line and breather filters
- Lubrication: oil filters for gearboxes, turbines and compressors
- Fuel: filters and water separators for gensets and boilers
- Air: intake filters for compressors and combustion engines
- Compressed air: coalescing, particulate and carbon filters
- Air-oil separators for screw compressors
Four types of filter — four different jobs
In hydraulics it is not pressure that wears parts out but particles. The clearances in a servo-valve spool and in a pump’s piston pair are measured in single microns, so a particle invisible to the eye acts as an abrasive. Here the filter is not an accessory of the circuit but the condition of its life.
- Suction — coarse pump protection, 60–150 µm, mesh
- Pressure — protects the valves after the pump, at full working differential
- Return — catches the wear generated by the circuit in a cycle
- Off-line loop — a separate pump cleans the tank outside the working cycle
- Tank breather — without it, air enters the tank together with dust
The lubrication system of a gearbox, turbine or compressor runs for years without being opened. The oil in it ages and collects wear debris, and the only thing standing between those particles and the bearing is the filter. What matters here is not only the rating but that the element survives a cold start.
- Pressure and return elements for lubrication systems
- Duplex housings switched over without stopping the machine
- Off-line fine filtration loop
- Air-oil separators for screw compressors
- Desiccant breather filters for tanks
A diesel genset most often fails to start not because of the engine but because of the fuel: water and dirt from the bottom of the tank reach the injectors first. Modern fuel equipment runs at high pressure with micron clearances and does not forgive water — which is why a filter and a water separator are fitted as a pair.
- Pre-filter — coarse cleaning and water separation before the pump
- Water separator — a coalescing element with a sediment drain
- Fine filter — protects the high-pressure pump and injectors after the pump
- Heating on cold sites — against wax formation
- A water sensor in the bowl, signalled to the panel
A compressor or engine passes thousands of cubic metres of air through itself every shift. Everything the intake filter fails to stop settles on the screw pair or ends up in the cylinder. Further down the line comes a second task — bringing the already compressed air up to the purity class the process requires.
- Intake filter — protects the machine itself, panel or cartridge
- Line particulate filter — solid particles in compressed air
- Coalescing — oil aerosol and moisture
- Carbon — residual oil vapour and odour
- Sterile — where air touches the product
Which standards we work to
| Parameter | Value |
|---|---|
| Hydraulics and oil | ISO 16889 — multi-pass, βx(c) |
| Fluid cleanliness | ISO 4406 — a code at ≥4, ≥6 and ≥14 µm |
| Fuel: particles / water | ISO 19438 (multi-pass with particle counting) / ISO 16332 |
| Intake air | ISO 5011 — efficiency, dust capacity, restriction |
| Compressed air | ISO 8573-1 (class: particles / water / oil) · ISO 12500 (oil aerosol carryover) |
| βx(c) and efficiency | β = 2 → 50%; β = 20 → 95%; β = 200 → 99.5%; β = 1000 → 99.9% (the «absolute» rating) |
| Rating range | hydraulics 3 · 5 · 7 · 10 · 16 · 25 µm; oil 1–25 µm; fuel 2–30 µm by stage |
| Media | glass fibre, cellulose, synthetic, wire mesh |
| Fuel flow range | ISO 19438: 50–800 l/h · ISO 16332: 50–1,500 l/h |
| Screw compressor separator | oil carryover about 2 ppm and below; ΔP when new 0.15–0.2 bar; replace at 0.5–0.7 bar; life 2,000–4,000 hours |
Target cleanliness code
The target code is set by the most sensitive component in the circuit, not the largest.
| Component | Target code |
|---|---|
| Servo valve, above 210 bar | 15/13/10 |
| Axial piston pump, 140–210 bar | 17/15/13 |
| Axial piston pump, above 210 bar | 16/14/12 |
| Directional valve, 140–210 bar | 20/18/15 |
| Gear pump, up to 140 bar | 20/18/15 |
Fresh oil from a drum is usually dirtier than the target code and needs filtering as it is filled.
What is most often forgotten in practice
- The rating is chosen not by eye but by the most sensitive component in the system
- A cross-reference is chosen from the element’s data sheet, not from how it looks
- Differential pressure is the only honest signal to replace; change by condition, not by calendar
- The bypass valve saves the pump, but at that moment the oil goes past the filter
- The clogging indicator lies on cold oil: viscosity alone creates the differential
- On a cold start viscosity is several times higher — the element must withstand the differential, not collapse
- Water in oil is more dangerous than dust: it kills the additives and starts corrosion
- A sharp ΔP rise after an oil change is almost always old sludge washed out of the system
- Water in diesel is not only corrosion but a growth medium for microbial fouling in the tank
- Saving on the pre-filter is paid for by repairing the fuel equipment; sediment is drained on schedule, not on alarm
- A coalescing element ages even without a ΔP rise: oil carryover grows before the differential does
- A carbon filter goes only after a coalescing one, otherwise it saturates instantly
What the right selection gives
- Pump and valve life instead of premature wear
- Stable flow and pressure in the circuit
- Replacement by condition, not by calendar
Industries
Equipment filter questions
How do you select a cross-reference filter?
From the element data sheet: rating, βx(c) efficiency, target ISO 4406 code, flow capacity and differential-pressure strength — not from how it looks. The rating is set by the most sensitive component in the system.
When should a filter be replaced?
On differential pressure — the only honest signal. But the indicator lies on cold oil, a compressor separator is changed at a ΔP of 0.5–0.7 bar, and a coalescing element ages even without a ΔP rise — oil carryover grows before the differential does.
What is an ISO 4406 code?
A fluid cleanliness code — three numbers for the particle counts at ≥4, ≥6 and ≥14 µm. The target code is set by the most sensitive component in the circuit: for example 15/13/10 for a servo valve above 210 bar and 20/18/15 for a gear pump up to 140 bar.
How is an ISO 8573-1 class read?
A notation such as 1 : 4 : 1 gives separate classes for particles, water and oil. The class is chosen for the process: painting, pneumatic tools, instrumentation and food production each need something different.
Why are a fuel filter and a water separator fitted as a pair?
Water and dirt from the bottom of the tank reach the injectors first, and modern fuel equipment runs with micron clearances and does not forgive water. ISO 16332 tests pressure-side separators with fine droplets and suction-side ones with coarse droplets: their working conditions differ.
Does new oil need filtering when it is filled?
Yes: fresh oil from a drum is usually dirtier than the target code. A sharp ΔP rise after an oil change is almost always old sludge washed out of the system.
Compressor filters in 3D
Compressor air intake filter, oil filter, air-oil separator and compressed-air line filter — construction and operating principle.
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