Sintered Porous Bronze Fuel Filters – Part 2
About depth filtration and the porous filter elements used in fuel filters
Some Details About Bronze, Depth Filtration, Porous Bronze Filter Elements and How to Make Them
What is bronze?
Bronzes and tin bronze
Traditionally, bronze is an alloy of copper and tin. Tin bronze is still the most common bronze alloy, and it usually has about 10 to 12% tin with copper making up most of the balance. Quite a few modern bronzes do not contain any tin at all.
Bronze alloys vary by the metals or non-metals added to the copper. Metallurgy groups different types of bronzes by the primary metal added to the copper. Some examples of this are aluminum bronze, phosphor bronze and silicon bronze.
The tin bronze alloy used for small sintered metal filters tends to be around 89 to 91% copper and about 9 to 11% tin.
What are sintered porous metals?
When small openings in metals are not defects
Fine, uniform metal powders are formed into useful shapes and then fused to make porous sintered bronze filter elements. The sintering powders are shaped by dies and fused by heat.
Carefully controlled particle fusion causes enough metal to diffuse between particles without allowing the part to become dense and solid. The result is a single piece of porous metal explicitly designed for filtration applications.
These porous metal filter elements are mechanically strong but have a capillary-like network of interconnecting pores running through the metal.
Why use sintered porous bronze as a filter element?
Porous bronze benefits
Sintered porous bronze filter elements are extremely tough and able to provide both surface and depth filtration. They provide
- High strength
- Uniform porosity
- High corrosion resistance
- A self-supporting structure
Greater particle-holding capacity
Depth filtration and particle capture
Porous sintered bronze filters provide both surface filtration and depth filtration. Depth filtration is all the interconnecting and winding pores and passages within the filter element's walls. Filter elements use depth filtration to capture and hold smaller particles not stopped at the filter element's outside surface.
Depth filtration captures smaller particles and holds onto more of them. It also does this without diminishing flow too much. Depth filtration is what makes sintered porous filter elements more efficient.
Over time though, the buildup of fine particles reduces flow through the filter element.
Sintered porous bronze depth filtration is efficient because of
What is porosity?
Porosity is the ratio of open space in a filter element compared to its total volume. Typically, a filter with high porosity has a more open structure and a higher flow rate. Together these increase its efficiency.
What is tortuosity?
Depth filtration is also efficient because of tortuosity. Tortuosity is the complex network of winding, interconnecting pores or passages through the filter material (filter media).
What are the advantages of porosity and tortuosity for depth filtration?
A larger number of interconnecting winding passages through the porous bronze (tortuosity) creates more opportunities for a filter element to capture small particles that would otherwise pass through the filter.
Particles small enough to not be captured on the filter's outer surface encounter many more potential obstacles down inside the filter media. Tortuosity gives depth filtration its higher particle holding or loading capacity.
Higher porosity means lower pressure drops across the filter
Porosity provides depth filters with lower pressure drops across the filter elements even as they hold onto more particles. They are considered efficient because of this.
Paper, actually polymer treated cellulose, and porous sintered bronze filter elements take advantage of depth filtration to capture finer particles. Porous sintered bronze is especially good at doing this while still allowing a relatively good flow rate through the filter.
Bronze filters are relatively compact, but paper filter elements need larger filter bodies. The surface area of paper elements needs to be large enough to provide usefully high fuel flow rates while still capturing fine particles.
Metal and plastic mesh screen filters only stop particles on the filter element surface. They cannot capture finer particles than their micron rating, but they do provide very good flow rates.
What is the process used to make sintered porous bronze filters?
Sintered porous bronze filter elements are made with bronze powders using the pressureless sintering process. Pressureless sintering is a type of powder metallurgy.
Sintered bronze filter elements start with a specific type of metal powder:
- Deoxidized particles
- Pre-alloyed bronze metal
- Very consistent particle sizes
- Highly spherical shaped particles
The powder is poured into dies and placed in specialized furnaces. Precisely controlled sintering conditions fuse the particles into porous but mechanically strong finished parts.
Some General Information About Plastic Inline Filters That Use Porous Sintered Bronze Filter Elements
Can sintered porous bronze filter elements be cleaned?
Engineers design small plastic inline fuel filters for easy replacement
Generally, plastic inline fuel filters need to be changed out regularly. The need to replace them is why OE small engine manufacturers and OEM aftermarket distributors provide so much support for OE replacement parts. They know the importance of protecting sensitive components that could be clogged or damaged by contamination. They also know that end users need replacement filters over the lifetimes of their machines.
Many manufacturers and aftermarket distributors recommend replacing plastic inline fuel filters at least once a year. Some go further and recommend replacing fuel filters as a part of routine maintenance after an internal combustion engine-powered machine comes out of storage.
Backwashing can extend the useful lives of both screen and sintered porous bronze filter elements, a definite design advantage for end users.
ITW 8411 (natural) and 8408 (red) Visu-Filters use a stainless steel mesh screen
Backwashing plastic inline fuel filters
What is backwashing?
Backwashing or backflushing is reversing flow through a filter or filtration sub-system to clean it and restore flow.
Backwashing a fuel filter can blow out accumulated particles and debris. This backwashing is an attempt to temporarily restore or at least improve fuel flow through the filter. Generally, backwashing with fuel or pressurized cleaning solvent successfully dislodges loose debris on the surface of both mesh screen and porous sintered bronze filter elements.
How well does backwashing a plastic inline fuel filter work?
Backwashing a mesh screen and sintered metal filter may restore much of its filtering capability. If necessary, they can backflush it to provide a temporary hold-over until they can find and install a replacement. Because sintered metal filters are depth filters, there is always a gradual buildup of finer particles that, bit by bit, clog up more and more of the tiny passages in a porous metal filter.
For this reason, plastic inline fuel filters with sintered bronze filter elements should be considered consumable items that end users must replace at some point. Recommended best practice is to replace plastic inline fuel filters as part of routine preventive maintenance.
Still, the ability to backwash a mesh screen or porous sintered bronze fuel filter and restore flow, even a reduced flow, reassures end users that they won't get stuck. Many Powersports users ride their machines into the backcountry. Backwashing a filter to restore or improve fuel flow means there is a much better chance they can return from the wild even if a filter begins to clog up.
Transparent and semi-transparent inline filter housing materials make it easier to inspect fuel filters for particle buildup. The benefits of visually inspecting filters are why many small plastic inline fuel filters use plastics that make it pretty easy to see particle accumulation on the filter element.
End users can tell just by looking if they should probably replace a filter. If necessary, they can backflush it to provide a temporary hold-over until they can find and install a replacement.
Because backwashing is useful, at least in the short run, sintered bronze fuel filter elements tend to be considered more practical than paper filter elements for off-road Powersports and Outdoor Power Equipment (OPE) used in remote locations.
ITW 8443 and 8416 Visu-Filters use a stainless steel mesh screen
Cross-section of flexible tubing pushed over a hose barb
Connection type is important for small plastic inline fuel filters
Why use hose barb connections on inline fuel filters?
Most plastic inline fuel filters use hose barb connections. These easily replaceable filters have hose barb connections (barbed inserts) designed to work with flexible hose and plastic tubing.
What about the fuel lines?
General-purpose gas-powered internal combustion engines and Powersports machines are likely to be exposed to gasohol (gasoline-ethanol blends) and even methanol now and then. Because of this, machine designers know it is probably best if their flexible fuel lines use materials that can stand up to a variety of fuels and fuel additives.
Flexible fuel line choice and durometer
Flexible fuel lines also need to be soft enough that the barbed hose connections can grip the fuel line's inner surface and create a tight seal.
Engine and machine design engineers are familiar with durometer ratings. They choose the right fuel line durometer and inner diameter (ID) to match the power system's barbed fittings. And they also opt for material compatibility with a variety of fuels and fuel additives.
Flexible fuel line fuel resistance
Experienced small engine designers and manufacturers build their engines always with the end user in mind. This perspective extends to their choice of fuel line tubing or hose. It is usually Tygon or a comparable fuel-resistant transparent tubing that does not turn brown and brittle after extended use.
The style of hose clamp matters
Most original equipment (OE) manufacturers provide pre-installed plastic inline fuel filters with hose barb connections. Their installation should include properly sized spring band clamps.
This clamp style ensures a durable leak-free connection because it can compensate for the fuel line's compression around the hose barb shank.
Spring band clamps also do a good job coping with the fuel line and hose barb diameter changes caused by temperature swings.
Original equipment small engines and high-quality OEM filters
Why plastic fuel filter quality matters
Original equipment (OE) machine manufacturers want to offer plastic inline fuel filters made by highly reputable original equipment manufacturers (OEM). Consistently high-quality replacement parts provide manufacturers with an economical way to increase end-user satisfaction.
Manufacturers do this by ensuring users can find the correct and best quality replacement parts when they need them. Using high-quality, consistent replacement parts and making them widely available enhances both the machine manufacturer and their engines' reputations.
Aftermarket distributors and original equipment replacement part suppliers have access to the same lineup of OEM plastic inline fuel filters as the OE manufacturers. This range of choice allows them to market OEM filters both as replacement parts and as aftermarket add-ons. They do this knowing they are offering highly reliable, durable parts that are less likely to fail unexpectedly.
Quality plastic inline fuel filters marketed as replacement and aftermarket parts provide
- Adequate filtration that protects engines
- Sizes that can be guaranteed to fit (genuine parts)
- Technical specifications that match engine requirements
- Materials and manufacturing methods that help prevent sudden failures
Plastic inline fuel filters that incorporate porous sintered bronze filter elements meet all of these requirements.
There is a bonus with fuel filters manufactured to meet industry standards like ANSI/OPEI B71.10-2018. Industry standards like this provide even greater assurance of sturdiness and durability in real operating conditions.
About this three-part series on sintered porous bronze fuel filters
Sintered Porous Bronze Fuel Filters - Part 1: Benefits of porous sintered bronze filter elements and how they are made >>
An overview of porous bronze filter elements, why they are so effective in small plastic inline fuel filters and what it takes to produce high-quality sintered porous bronze fuel filters.
Sintered Porous Bronze Fuel Filters - Part 2: About depth filtration and the porous filter elements used in fuel filters >>
More detail about bronze, porous sintered bronze filter elements as depth filtration, how to make them, and their installation and use.
Sintered Porous Bronze Fuel Filters - Part 3: Porous sintered bronze elements FAQ, applications beyond filtration plus references >>
An FAQ about sintering, porous sintered bronze fuel filter elements and depth filters. It also includes an overview of other applications that use porous bronze filter elements, plus a list of references.
Selected ITW Fastex Filtration Visu-Filter fuel filters
ITW Fastex Filtration and ITW Powertrain Components Visu-Filter fuel filters are compliant with ANSI/OPEI B71.10-2018.
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