When to Change Your Filters
How to know when a filter needs replacement—and why changing too early or too late both cost you money.
The Two Costly Mistakes
Changing Too Early
Wasting money on filters that still have life. A filter isn't "used up" just because time has passed.
Changing Too Late
Bypass opens, unfiltered fluid damages components. One pump failure costs more than years of filters.
The Right Way: Differential Pressure
The only reliable way to know when a filter needs changing is differential pressure (ΔP)—the pressure difference between the inlet and outlet of the filter. As the filter loads with contaminant, ΔP increases until it reaches a point where the filter should be changed.
How It Works
Filter Change Indicators
1. Visual Indicators (Pop-ups)
Many hydraulic filters have a visual indicator that pops up when differential pressure reaches a set point (typically 25-30 psi). These are useful but have limitations:
✓ Pros
- • Easy to see during walkarounds
- • No additional cost
- • Works without power
✗ Cons
- • Cold oil can trigger false alarms
- • Only shows "change now"—no warning
- • Must physically check the filter
2. Electrical Indicators
These send a signal to the control panel when ΔP reaches the setpoint. Better for remote monitoring and machines with enclosed filter housings.
3. Continuous ΔP Gauges
The best option—shows actual differential pressure at all times. Lets you trend filter loading and predict when changes will be needed.
Cold Start Warning
Differential pressure increases dramatically when oil is cold. A filter that shows 30 psi ΔP at startup may drop to 10 psi once the system warms up. Always check indicators at operating temperature.
Typical Filter Change Intervals
If you don't have ΔP monitoring, here are starting-point intervals. Adjust based on your actual conditions:
| Filter Type | Typical Interval | Factors That Shorten Life |
|---|---|---|
| Hydraulic & Lube Oil | ||
| Hydraulic return line | 500-2000 hours | Dirty environment, worn components |
| Hydraulic pressure | 1000-3000 hours | Pump wear, system contamination |
| Hydraulic suction | 2000-4000 hours | Tank contamination, poor breathers |
| Lube oil (engine) | 250-500 hours | Fuel quality, duty cycle, age |
| Compressed Air | ||
| Particulate filter | 4000-8000 hours | High dust intake, undersized compressor |
| Coalescing filter | 4000-8000 hours | High oil carryover, dryer issues |
| Carbon/adsorption filter | 4000-8000 hours | High vapor load, upstream filter failure |
| Compressor inlet | 2000-4000 hours | Dusty environment, poor pre-filtration |
| HVAC & Air Filtration | ||
| HVAC panel filter (MERV 8) | 30-90 days | Outdoor air quality, construction dust |
| HVAC bag/rigid filter (MERV 11-15) | 6-12 months | High occupancy, poor pre-filtration |
| HEPA filter (MERV 17+) | 2-5 years | Inadequate pre-filters, process dust |
| Dust Collection | ||
| Cartridge collector | 6-24 months | Fine dust, poor pulse cleaning, high loading |
| Baghouse filter | 2-5 years | Abrasive dust, moisture, chemical attack |
| Engine & Fuel | ||
| Fuel filter | 500-1000 hours | Fuel quality, water contamination |
| Engine air filter | 500-1500 hours | Dust, debris, poor pre-cleaners |
Signs You're Changing Filters Wrong
Changing on calendar time only
"Every 3 months" ignores actual usage. A machine running 24/7 needs changes more often than one running 8 hours a day.
Ignoring bypass indicators
Once bypass opens, you're sending unfiltered fluid through your system. Every minute of operation is causing damage.
Filters always look "clean"
If removed filters look spotless, you're changing too early. Some discoloration and visible loading is normal and expected.
Filters always collapsed or damaged
If filters are collapsing, you're waiting too long OR using undersized filters. Check your ΔP limits and filter sizing.
Maximizing Filter Life
Keep contaminants out
Use desiccant breathers, seal reservoir openings, filter new oil before adding. Every particle you keep out is one the filter doesn't have to catch.
Use the right filter size
Undersized filters plug faster. If you're changing filters frequently, you may need a higher dirt-holding capacity element.
Add offline filtration
A kidney loop filter cart continuously polishes the oil, taking load off system filters and extending their life.
Track and trend
Log filter changes and hours. Over time you'll see patterns and can predict changes instead of reacting to failures.
Need Help Optimizing Filter Changes?
We can help you evaluate your current filter program and find opportunities to reduce costs while improving equipment protection. Send us your filter specs and change intervals.
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