Filter-Regulator-Lubricators (FRLs)
are available in several different configurations:
- - individual components
- - combination filter-regulator
("piggyback"shown below)
- - two-unit modular combinations
- - three-unit modular
combinations
Filter, regulator, lubricator (FRL)
assemblies are pre-packaged or modular assemblies of common
configurations of air filters, regulators, lubricators, and
gauges. Important specifications to consider when searching
for filter, regulator, and lubricator assemblies include regulator
type, media, performance specifications, adjustment control,
connectors or pipe size, body material, features, and environmental
parameters.
The piggyback (fig. FRL1-1) and
modular FRL's (fig. FRL1-2) have space-saving designs. The
piggyback has a filter and a regulator stacked on top of each
other. Modular design allows for easy installation and removal of
components.
The filter itself may be for depth
filtration, edge filtration, or coalescing. Regulators may be of
the piston or diaphragm design. FRLs are used in compressed air
systems in various industries for numerous applications.
- - Medical: dental
equipment, oxygen concentrators/enrichers, respirators, hospital
air systems, hospital lab air systems, drug manufacturing and
packaging
- - Electronics:
console controls, testing equipment, circuit board manufacturing,
silicon water handling/manufacturing, assembly computers
- - Packaging:
filling equipment, sealers, boxers, coders, wrapping, palletizers,
can and bottle manufacturing, labelers, cleaners, glue
dispensing
- - Textiles:
industrial sewing machines, industrial laundry equipment, dry
cleaning equipment, looms
- - Printing:
presses, ink flow regulators, photocopier equipment, carton
loaders, stencil transfer machines, engraving machines
- - Food: beverage
dispensing equipment, produce sorting, meat processing,
canning/bottling
- - Automotive: tire
changing equipment, lifts, pneumatic tools, paint spraying, sand
blasting
- - General
manufacturing: actuators, pneumatic tools, air hoists,
automation equipment, instrumentation
FRL Filters: Filters (fig. FRL1-3)
eliminate pipe scale, dirt, rust, and moisture from compressed air
lines. Proper filtration is critical to maximize the dependability
and longevity of a compressed air system. Do not install a filter
with a finer rating than necessary. Although it will not hurt
downstream equipment, it will drive up the system operating cost.
Particle-removal filters should be chosen based on the following
factors:
- - scfm
- - acceptable pressure drop
- - pipe connection size
A filter with bigger body size will
create less initial pressure loss and provide longer operating life
than a smaller filter with the same removal ratings.

Coalescing filter elements are
available based on micron size.
Choose a coalescing filter and element based on the
following factors:
- - acceptable oil carryover
- - expected airflow rate
- - pipe connection size
Absorption-type filters, used in food
processing or breathing air, normally contain activated carbon
granules, which absorb and hold hydrocarbon vapors.
Install an appropriate number of
drains valves upstream of the filter. These drain valves will
assist in the removal of excess condensate and contaminants, as
well as provide additional protection for the filters.
Filter bowls will collect condensate
and require drain valves. The majority of filter bowls are made
from polycarbonate or metal.
CAUTION:
Polycarbonate bowls are suitable for use in normal industrial
environments, but should not be located in areas where they could
be subjected to direct sunlight, an impact blow, nor temperatures
outside of the rated range. Polycarbonate bowls should not be
exposed to chlorinated hydrocarbons, ketones, esters and certain
alcohols. They should not be used in air systems where compressors
are lubricated with fluids such as phosphate ester and di-ester
types.
Metal bowls are good to use where
ambient and/or media conditions are not compatible with
polycarbonate bowls. Metal bowls can resist the effects of most
solvents, but should not be subjected to salt laden atmospheres or
used where strong acids or bases are present. Metal bowl guards are
recommended for all applications, and can even protect a
polycarbonate bowl from damage.
FRL Regulators: Regulators (fig.
FRL1-4) govern line pressure changes and deliver a constant outlet
pressure to the downstream air components. There are relieving and
non-relieving types of regulators. Relieving regulators let air
escape should the downstream pressure surpass the desired regulated
pressure. In this event the excess pressure will cause the
diaphragm to move upward against the control spring, open the vent
hole, and vent the excess pressure to the atmosphere through the
hole in the bonnet. One type of regulator uses a
balanced-poppet-style valve. As downstream pressure increases, it
pushes on the bottom side of the diaphragm, balancing against the
force of the spring. The poppet throttles the orifice to restrict
flow and produce the desired downstream pressure. A spring under
the poppet ensures that the valve closes all the way when there is
no flow present. (Because the poppet is pressure-balanced to
maintain good stability, the effects of output pressure
fluctuations cancel out, which upgrades sensitivity and response
and lessens droop, or loss of pressure.)

Larger capacity regulators include
their own separate diaphragm chamber, which has an aspirator tube
exposed to the output pressure. As the flow increases through this
regulator, the aspirator tube provides a slightly lower pressure in
the diaphragm chamber. The diaphragm is pushed downward and opens
the orifice without reducing the output pressure. Therefore, this
kind of regulator has minimal droop (output pressure decay) as
supply pressure varies.
Lubricators: Lubricators (fig.
FRL1-5) provide a constant oil-air mixture to lubricate downstream
air equipment for reduced friction and wear. High-velocity air
passes through a venturi, and draws the oil through a capillary,
then drips it into the air-stream. The moving air breaks up the oil
into a mist or fog, which is then transferred downstream into the
air-powered machine. There are also micro-mist lubricators, which
lubricate through tiny holes, creating a fine mist. They are
usually chosen based on pipe connection size, oil reservoir
capacity, and acceptable pressure loss versus flow rate. Inside the
lubricator are bowls to collect accumulated liquid condensate.
These bowls are made from either polycarbonate or metal.

CAUTION:
Polycarbonate bowls are suitable for use in normal industrial
environments, but should not be located in areas where they could
be subjected to direct sunlight, an impact blow, nor temperatures
outside of the rated range. Polycarbonate bowls should not be
exposed to chlorinated hydrocarbons, ketones, esters and certain
alcohols. They should not be used in air systems where compressors
are lubricated with fluids such as phosphate ester and di-ester
types.
Metal bowls are good to use where
ambient and/or media conditions are not compatible with
polycarbonate bowls. Metal bowls can resist the effects of most
solvents, but should not be subjected to salt laden atmospheres or
used where strong acids or bases are present. Metal bowl guards are
recommended for all applications, and can even protect a
polycarbonate bowl from damage.
FRL
Installation and Maintenance Requirements
- If the filter's purpose is to remove
moisture, an automatic float-type drain should be installed to
periodically remove condensate from the filter bowl. These bowls
are normally transparent, allowing for easy visual inspection of
the sump level. If a filter could be subjected to conditions where
pressure is above 150 psig (10.3 bar), temperatures are below 40°F
(4.44°C), or temperatures are above 120°F (48.89°C); a metal bowl
rather than the polycarbonate bowl is required. This also holds
true when synthetic compressor lubricants are present, as these
often contain chemicals that are harmful to polycarbonate.
- Always install a filter upstream
from a regulator to protect its internal passages. It is crucial to
set the regulator's desired output pressure under normal flow
conditions.
- In a lubricator, a manual adjusting
valve sets the oil drip-rate, and a sight glass allows the operator
to monitor the output. A fill plug provides access to refill the
reservoir.
- In combination units,
interconnections are often made through modular face connectors.
These connectors allow simple removal of components for servicing
or cleaning.