A hydraulic filter can be cleaned and reused only if it features surface-type metal media, such as stainless steel wire mesh or sintered metal. Conversely, disposable depth filters manufactured from cellulose or synthetic micro-glass fibers cannot be cleaned or reused, because liquid flushing permanently collapses their internal pore structure and Beta ratio.
Cleaning disposable hydraulic filters leads to catastrophic component damage, pump cavitation, and premature valve failure.
Hydraulic Filter Cleanability by Media Type
Before attempting maintenance, technicians must identify the internal filter media. Hydraulic filters are classified into two distinct engineering categories: surface-type filtration media and depth-type filtration media.
Why Disposable Cellulose and Micro-Glass Filters Cannot Be Cleaned
Modern industrial power units rely primarily on synthetic micro-glass filter elements to protect proportional valves and axial piston pumps. These elements function through depth filtration, trapping contaminants within an intricate microscopic matrix.
Attempting to clean depth filters with compressed air or chemical solvents causes two irreversible mechanical failures:
1. Structural Channeling and Fiber Fracture
High-pressure air streams rupture the fine borosilicate fibers within micro-glass elements. This fiber fracture creates microscopic channels through the media. While the filter exterior may appear clean, particulate contamination passes directly through these enlarged channels, circulating abrasive silts into precision-fit directional control valves.
2. Collapse of the ISO 16889 Beta Ratio
Filter capture efficiency is governed by the Beta Ratio (β) under the ISO 16889 multi-pass test standard:
A new micro-glass element exhibits a rating of β10 ≥ 200, representing an efficiency of 99.5% for particles 10 microns and larger. Chemical solvent cleaning strips the resin matrix, reducing the rating to β10 < 2 (less than 50% efficiency). The cleaned filter ceases to provide fluid power protection.
Protocol for Cleaning Reusable Stainless Steel Mesh Elements
Stainless steel wire cloth filters serve as surface filters where contaminants collect solely on the exterior wire face. These elements are standard in suction strainers and low-pressure return lines.
Safe Ultrasonic Cleaning Procedure:
- Solvent Pre-Rinse: Submerge the wire mesh element in a clean petroleum-based degreaser to dissolve outer grease cakes. Avoid using chlorinated hydrocarbons.
- Ultrasonic Agitation: Place the stainless element into an ultrasonic cleaning tank filled with an aqueous surfactant solution. Ultrasonic cavitation dislodges embedded silt from wire intersections without physical distortion.
- Reverse Flow Flushing: Flush filtered compressed air or clean solvent from the inside of the element outward (back-flushing).
- ISO 2942 Bubble Point Integrity Testing: Submerge the cleaned filter element in isopropanol and apply regulated internal air pressure. Verify that air bubbles do not emerge below the rated pore threshold pressure, confirming zero mesh punctures.
The Bypass Valve Risk in Reused Hydraulic Filters
Every inline filter housing contains a mechanical differential pressure bypass valve. When a contaminated or improperly washed filter element is installed, high differential pressure (ΔP) develops rapidly across the clogged internal pores.
This pressure spike forces the housing bypass valve open. Once open, unfiltered hydraulic oil circulates directly from the reservoir into your hydraulic piston pumps and valves, accelerating abrasive wear according to ISO 4406 cleanliness codes.
Economic Evaluation: Replacement Element Cost vs. Component Overhaul
Reusing disposable filter elements to reduce operational expenses introduces disproportionate financial liability into fluid power management:
- Cost of New Micro-Glass Return Filter: $60 – $150
- Cost of Piston Pump Rebuild (e.g., A10VSO Series): $3,500 – $8,500
- Unscheduled Manufacturing Downtime Loss: $800 – $4,000 per operational hour
- Hydraulic Fluid Flushing and ISO 4406 Remediation: $1,500 – $3,000
Engineering Recommendation:
Do not wash disposable elements. To optimize operating costs, monitor fluid health using scheduled fluid analysis rather than cleaning spent media.
For technical sizing data, micron ratings, and compatible housing specifications, review our complete guide on industrial hydraulic filter elements (including direct equivalents for Hydac and Pall). Contact our engineering team for replacement cross-reference support.