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Compatibility of Filter Media with Hydraulic Fluids

The Filter Guys

Compatibility of Filter Media.

Filter media can be divided into two broad categories, natural fibres (usually cellulose) and synthetic or man made fibres (usually fibre glass or woven wire mesh), although many different variations and types of media do exist, many filters fall into one of these two categories.

Fluid to be Filtered Recommended Media
Petroleum-based Cellulose, Glass fibre
Phosphate Ester Glass Fibre
Diester Glass Fibre
Water Glycol Glass Fibre
Water-Oil Emulsion Glass Fibre
Biodegradable Fluid HWCF* Glass Fibre
Course Filtration Wire Mesh

* High water content filtration

Notes on seals:

Filters with seals made of BunaN are appropriate for most applications involving petroleum oil and some high water content fluids. Filters with seals made of Viton® of Fluorel® (both fluoroelastomers) are required when using diesters, phosphate ester fluids.

(Viton and Fluorel are registered trademarks of DuPont Dow Elastomers and 3M)

How Filter Media Functions In a Filtration System

The Filter Guys

How Filter Media Functions. The job of the media is to capture particles and allow the fluid to flow through. For fluid to pass through, the media must have holes or channels to direct the fluid flow and allow it to pass. That’s why filter media is a porous mat of fibers that alters the fluid flow stream by causing fluid to twist, turn and accelerate during passage.

The fluid changes direction as it comes into contact with the media fibers, as illustrated above. As the fluid flows through the media, it changes direction continuously as it works its way through the maze of media fibers. As it works its way through the depths of the layers of fibers, the fluid becomes cleaner and cleaner. Generally, the thicker the media, the greater the dirt-holding capacity it has.

Looking at a cross-section view of the fibers:

we can see how the flow stream is accelerated as it flows into the spaces between the fibers.

This is applies to all liquid filters, be they oil, fuel, water of water glycol. For more information on filtration products and replacement elements please contact us for a chat. We’re here to help.

How Filter Media Collects Particles

The Filter Guys

How Filter Media Collects Particles. There are four basic ways media captures particles.

The first, called inertia, works on large, heavy particles suspended in the flow stream. These particles are heavier than the fluid surrounding them. As the fluid changes direction to enter the fiber space, the particle continues in a straight line and collides with the media fibers where it is trapped and held.

The second way media can capture particles is by diffusion. Diffusion works on the smallest particles. Small particles are not held in place by the viscous fluid and diffuse within the flow stream. As the particles traverse the flow stream, they collide with the fiber and are collected.

The third method of particle entrapment is call interception. Direct interception works on particles in the mid-range size that are not quite large enough to have inertia and not small enough to diffuse within the flow stream. These mid-sized particles follow the flow stream as it bends through the fiber spaces. Particles are intercepted or captured when they touch a fiber.

The fourth method of capture is called sieving and is the most common mechanism in hydraulic filtration. As shown at right, this is when the particle is too large to fit between the fiber spaces.