Filter separator

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General Description

Forain filter separators are designed for those applications where high efficiency removal of solid and liquid particles is required. The use of these separators is the best solution to remove very fine mists, aerosols and slugs from gas flow. Lubricating oil from process gas, entrainments in natural gas lines upstream compressor stations and reducing and metering stations can be considered additional applications for this kind of product.

In case of a uniform distribution of liquid particles, either the FSO horizontal type or the FSV vertical type is preferred. Horizontal Filter Separator can be vertical as well and it is normally equipped with quick opening closure to reduce maintenance time to a minimum.

Principle Of Operation

The removal of larger particles is obtained at the inlet of gas into the filter separator by combining the impingement force of the shell surfaces and the gravitational effect due to the decrease of gas velocity. The first stage, consisting of disposable filter elements chosen according to the operating conditions, has the purpose to remove the smallest solid particles and to coalesce the mists. Remaining liquid particles are separated in the second stage through the vane unit.

The collected particles are properly drained through a dedicated drain system. Complete automatic drain system complete with valves and instruments can be supplied by Forain on request


The FSO and FSV types are guaranteed to remove 100% of all droplets 5 microns and larger and 99.5% of those droplets with size 0.5 to 5 microns. The separation efficiency of solids is 100% of particles 3 microns and larger and 99% of those 0.5 to 3 microns.

Pressure Drop

The total pressure drop can vary from 300 to 1000 mm of water column considering clean filter elements. Anyway, these values can change according to customer requirements and according to process conditions.


The most important point to consider when installing Forain Filter Separator is to get the gas flow going into the right direction and to connect the process piping according to drawing. Forain Filter Separator is normally shipped with the required number of removable filter elements already installed inside the separator, which is ready to be put into operation.


Forain Filter Separator is sized by considering the pressure drop with clean filter cartridges in the presence of a certain flow of gas. Forain Filter Separator is equipped with two nozzles for installation of a differential pressure measuring device (the instrument can be supplied from Forain on request).

Filter Separator can be operated without any decrease in separation efficiency up to the maximum  foreseen design pressure drop. It is recommended to replace the filter elements when the value of pressure drop required by the process is reached (obviously respecting the maximum limits). For applications with methane gas, it is recommended to replace the filter elements every 2 years. It should be taken into account that lifetime and duration of filter elements depend on the type and nature of particles present in the process fluid.

Precaution is necessary while starting up the unit during the pressurization of filter separator. It is necessary to open slowly and gradually the block valve present on the inlet of vessel in order to avoid the damaging of filter elements (inlet and outlet valves can be supplied by Forain on request).


Filter separator offers the advantage of a minimum maintenance. The replacement of filter elements is the only required maintenance and it is recommended when the differential pressure reaches the maximum pressure value for which the filter elements are designed. This is a simple operation, as the filter elements can be easily removed through the available quick opening closure.

Forain Filter Separator type does not require any particular maintenance. For the first stage, maintenance shall be carried out only when it is necessary to replace the filter elements. The vane unit is self-cleaning. Upon customer request, also the second stage (vanes unit) can be supplied of removable type.

Filter elements are made of combustible material; before proceeding with quick opening closure opening, filter separator must be completely depressurized and purged with nitrogen. After that, filter separator will be definitively depressurized.

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