Coalescer Cartridges for Aviation & Industrial

Velcon Coalescers

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Coalescer Cartridges - Data Sheet #VEL1732


Velcon Coalescers

Coalesced water drops releasing from the knitted sock at the outside surface of the cartridge

Velcon Coalescers

Velcon Coalescers


Coalescer cartridges are employed as the first stage in filter/separator vessels for hydrocarbon fluids. They perform two functions: (1) coalesce (combine) highly dispersed, emulsified water particles into larger water drops and (2) filter-out particulate contaminants.


The top photo shows a highly magnified view of the coalescing process. Tiny droplets of water contact and adhere to strands of fiberglass. Flow pushes the droplets along the strand until they reach an intersection of strands where they combine with other droplets (coalesce) into large drops.

These large drops are then carried to the outside surface of the cartridge. Having a higher specific gravity than the hydrocarbon fluid, they release and settle to the bottom of the vessel. The larger the drops, the faster and more efficiently they fall out. (See photo to the right.) In general, particle removal efficiency increases with coalescing efficiency. This is accomplished by employing a tighter, finer filtration media.

Flow direction is from inside to outside of the cartridge. This minimizes surface velocity and helps prevent the water drops from breaking up and being carried downstream.


Coalescer cartridges are used primarily to coalesce emulsified water and remove particles from hydrocarbon fluids. The largest single application is the filtration of aviation jet fuel. They are also used with other types of fuels, process in refineries and petrochemical plants, and condensate

Other liquids can be separated if they are immiscible, the specific gravities differ, and high concentrations of surface active agents are not present. As a rule of thumb, if a sample of the mixture readily separates in an hour or two, a coalescer can probably be used. If the mixture hasn’t separated after 24 hours, coalescing probably won’t work.


Velcon single-unit coalescer elements are offered with Threaded Base or Open Ends and with Fiberglass Media or Fiberglass and Pleated Media combinations.

Threaded Base Coalescers are recommended for use in most applications. They simplify installation and replacement by eliminating the need for cover plates, center plates, nuts, washers, and gaskets. They are for use in Velcon and other make filter/ separators. Threaded base adapters are available to convert vessels presently using open end elements.

Open End Coalescers are offered with single unit construction which reduces the number of gasket seals and improves overall reliability.

All-fiberglass Media Coalescers combine depth particulate filtration with a deep coalescing structure. All-fiberglass designs have successively finer media layers to achieve depth-type filtration of particles.

Combination Fiberglass and Pleated Media Coalescers remove particles primarily in the high surface area pleated core. They have one or more layers of pleated media inside a cylinder of molded fiberglass laminations to provide an extended surface area for particulate filtration. Pleat corrugation and separation materials are used to keep pleats open for full utilization.

Coalescing and filtration performance depends largely on the fiber diameter and bulk density of the fiberglass media. Both the All-Fiberglass and the Combination coalescer cartridge designs incorporate phenolic resin impregnated fiberglass media. Several grades with fiber diameters ranging from 1 to 10 micrometers are used in various combinations to achieve desired results. Velcon’s latest coalescer designs (85, 87 and C5 series cartridges) achieve even higher filtration and coalescing efficiency by incorporating pure micro-glass fibers with diameters of less than 1 micrometer in the pleated media.

Velcon Coalescers     Velcon Coalescers


Model Number System. Refer to the box at right. The one or two digit Series Designator relates to the approx­imate micron rating of each model coalescer cartridge. Note that this is a nominal rating and should be used for reference only.

The “0”, “2”, and “4” Series all-fiberglass cartridges are rated at 25, 5, and 3 microns respectively. The “2” and “4” Series are commonly used with diesel and other fuel oils, and are a compromise between filtration efficiency (cart­ridge life) and water removing capability. They coalesce gross water, but normally do not remove fine water haze.

The all-fiberglass “6” Series was originally developed for jet fuel service (the original MIL-F-8901 specification). With a 2-micron rating, it has proven to be the most cost effective design in some jet fuel applications. “6” Series cartridges are also used in gasoline filtration service. However, it should be noted that the powerful detergent additives in most automotive gasolines reduce the coalescing capability of this and other cartridge designs.

“83” Series Cartridges. The 1-micron rated “83” Series is a pleated media/fiberglass cartridge. The very practical “83” Series cartridges have become the most widely used design in applications including gasoline, condensate, and insulating oil filtration.

“85” and “87” Series Cartridges. The “85” Series is rated at 0.5-micron while the “87” Series is rated at 0.3 micron. Both incorporate multi-layered pleated media. The “85” Series has consistently shown superior dirt holding capacity in the field.

EI* 1581 Fifth Edition Cartridges. I-6xxC5 (TB), I-6xxMM, and I-6xxA4 Series of coalescers incorporate a multi-layered pleated media designed to provide superior dirt holding capacity in the field, combined with 0.4 micron efficiency. The I-6xxC5 (TB) replaces both the I-6xx85 (TB) and I-6xx87 (TB) cartridges. These cartridges are available in either threaded base or open-end configuration. See data sheets 1923 and 1934 for more specific information on EI 1581 Fifth Edition.

Cartridge Dimensions. 6” diameter cartridges are the current industry standard. They are offered in lengths of 11”, 14”, 22”, 28”, 33”, 38”, 44”, and 56”. However, not all series are available in all lengths or in both end cap designs. Contact your Velcon Distributor for details.

4” diameter cartridges are also offered for use with older equipment. They are available in a variety of lengths ranging from 8 to 40 inches.

Velcon Coalescers

*EI (Energy Institute) is the new specification authority. API (American Petroleum Institute) is no longer involved in aviation fuel filtration specifications.


Coalescer Cartridge and Filter/Separator

Vessel Selection Guidelines

Aviation Fuel Filtration in commercial applications is governed by the complex, stringent requirements of EI Publication 1581, Fifth Edition. Refer to the appropriate Velcon literature or contact your Velcon Representative for assistance.

For non-aviation applications the following guidelines have proven to be useful. Note, however, that these guidelines are general in nature and should be used for guidance only.

1. Determine total length (inches) of 6” diameter cartridge required: 

a. Find the approximate viscosity of your hydrocarbon fluid on the Chart Y-axis.

b. Find the corresponding Specific Flow Rate (gpm/inch) on the X-axis.

c. Divide Total Flow Rate (gpm) of your application by this Specific Flow Rate to calculate total inches of coalescer required.

2. Select cartridge model and calculate quantity required:

a. Choose model (type and length) cartridge to use. 83 Series Coalescers are recommended for most applications. Other types and sizes are offered for special applications.

b. Calculate minimum number of cartridges required by dividing total inches (from Step 1) by length of cartridge selected.

3 Select the Filter/Separator Vessel for your application:

a. Refer to the Velcon literature for HV (horizontal) or VV (vertical) Filter/Separators.

b. Find the appropriate vessel for the model and quantity Coalescer Cartridge selected in Step 2.

Velcon Coalescers