FRL Unit: Filter, Regulator, & Lubricator - How They Work

FRL unit

Figure 1: FRL unit

Filter, regulator, and lubricator (FRL) compressed air systems are used to deliver clean air, at a fixed pressure, and lubricated (if needed) to ensure proper pneumatic component operation and increase their operation lifetime. The air supplied by compressors is often times contaminated, over pressurized, and non-lubricated meaning that an FRL unit is required to prevent damage to equipment. Filters, regulators, and lubricators can be bought individually or as a package (as seen in Figure 1) depending on what is needed to ensure the proper air specifications are being met for downstream equipment. It is recommended to install these devices if you:

  • Use pneumatic tools and equipment;
  • Are installing an HVAC system;
  • Require clean air to be delivered to your facility or workplace;
  • Require compliance to ISO, OSHA, ASHRA or other air quality standards;
  • Want to improve the service life, safety and reliability of your air system.

FRL Unit Online Selection

Table of Contents

What do FRL units do?

An FRL unit is comprised of a filter (F), regulator (R), and a lubricator (L). They are often used as one unit to ensure clean air in a pneumatic system but can also be used individually. Having a proper FRL unit installed in a pneumatic system provides higher reliability of the components downstream, reduced power waste due to over pressurization, and increased component lifetime. The three components work together to do the following:

  • Filters remove water, dirt and other harmful debris from an air system. This is often the first step in improving the air quality.
  • Regulators adjust and control the air pressure of a system to ensure that down-line components do not exceed their maximum operating pressures. This is the second step in the FRL system.
  • Lubricators reduce the internal friction in tools or equipment by releasing a controlled mist of oil into the compressed air. This is often done last and/or right before the component needing lubrication.

What FRL components do you need?

Filters, regulators and lubricators can be purchased individually or as a combined filter-regulator (FR) or filter-regulator-lubricator (FRL) unit. It is recommended to install an FR unit if your equipment is self-lubricating and an FRL unit if your equipment requires lubrication. It is important to understand the air requirements of your system and components to know if and what components of an FRL unit are needed. The type of FRL components required is dependent on your system requirements, but it is recommended that every air system uses at least one filter and one pressure regulator. Most modern pneumatic tools use self-lubricating seals and as such, you often do not need to install a separate lubricator. If they aren’t self-lubricating, a lubricator should also be installed in the system. As a general rule, a pneumatic system’s order of installment is in this order: compressor, filter, regulator, and then a lubricator. Give careful consideration to the location of these devices because you may not need to treat your entire air system. To optimize the pneumatic system and reduce cost, only treat air where air needs to be treated.

Application specifications to know

Before selecting a device, it is important to know the pressure, flow rate, and air quality requirements of the tools using compressed air and if any air quality standards apply to your workplace before selecting a device. To ensure that your FRL unit, or component, meets the pressure ranges in and out the flow rate requirement (typically in liters per min) consult the datasheet for your specific unit. Also, the environment that the device will be installed in and exposed to should be considered. Housings come in different materials to accommodate different environmental conditions. We recommend a metal housing if the device will be installed outside, exposed to heat, salt water, salt air, or chemicals. Nylon or polycarbonate housing is acceptable for most general applications. It is recommended to consult our selection guide for material compatibility for each application.

Pneumatic filter selection

Pneumatic filter

Figure 2: Pneumatic filter

Filters remove water, dirt and other harmful debris from an air system (Figure 2). The type and size of contaminants present in the system and the air requirements for components will ultimately affect what micron size and bowl material is needed for the filter. Common applications generally only require a filter rated between 5-40 microns. However, ISO 8157 goes down to 0.1 micron and for special applications, like medical or pharmaceutical the specifications can be as low as .001 micron. The rating means that it doesn’t allow bigger particles through. For example, if you have a 20 micron filter it will allow particles smaller than 20 microns to pass through. It should be noted that filters experience a small pressure drop across the inlet and outlet ports because of the flow restriction. A 0.1 micron filter will create a larger pressure drop than a 40 micron filter and will require more regular maintenance due to the easy buildup of contaminants. Therefore, do not oversize your filter by selecting the finest possible micron size. It will lead toto higher cost for the component, a larger pressure drop, and more maintenance time. Instead, select a filter that will remove only the smallest contaminant specific to your system.

The bowl material and drainage type are also important. The bowl comes into contact with the contaminants and houses the filtered particles. The pressure, temperature, and chemicals present affect the bowl material selection. Filters also require drainage, which can be either accomplished by the filter as an automatic, semi-automatic, or manual drainage system or a condensate drain can be attached to the outlet to remove the filtered contaminants.

  • Automatic: An automatic drain is a 2/2-way valve that closes when the system is pressurized. It has a float system in it that rises when the system is de-pressurized or when liquid accumulates, and this rise in the float causes the drain to open. Advised when the equipment is in continual use, requires frequent drainage, or in a hard to reach location.
  • Semi-automatic: A semi-automatic drain automatically drains the system upon de-pressurization. It can drain the system when pressurized, but only by a manual process. If the system is not always under pressure, it is recommended to have a semi-automatic drainage filter.
  • Manual: The filter can be manually drained when the system is depressurized. Not advised for a hard to reach location, if it requires frequent drainage, and if the system isn’t regularly depressurized.
  • Condensate Drain: A condensate drain can be attached to the outlet of the filter to accomplish the drainage. However, proper timing of the open/closing needs to be set.

Pneumatic pressure regulator selection

Pneumatic pressure regulator

Figure 3: Pneumatic pressure regulator

Regulators, also called pressure reducing valves, adjust and control the air pressure of the system to ensure that down-line components do not exceed their maximum operating pressures (Figure 3). Two of the most important selection criteria are the pressure rating and if it is a relieving or non-relieving regulator. It is important to include a safety factor on the max input pressure so that the regulator can handle excess pressure. Typically, a regulator’s manual will have a flow curve to allow a user to correctly size a regulator based on the system flow rate and desired outlet pressure. Regulators also provide a consistent and stable outlet pressure. If you need to regulate your pressure to 0.6 MPa, we recommend that you select a regulator having a maximum range of 1MPa instead of 0.7 MPa to ensure that you do not damage the regulator if your system becomes over pressurized. In addition, if the inlet pressure is too high for a single device, two pressure regulators in a row can be used to decrease the pressure in two stages. On common pressure regulators, it is a manual knob to set the output pressure.

The second consideration is if the regulator is considered relieving or non-relieving. Relieving regulators have a built-in vent that lets excess pressure escape once it exceeds a certain threshold. Non-relieving regulators will not vent this excess pressure and rely on a secondary device to decrease pressure. For a non-toxic application, a relieving regulator is recommended to ensure that a buildup in pressure doesn’t occur and cause damage. However, when the application consists of dangerous or expensive gases, you do not want to release them into the atmosphere.

For a more detailed technical article on pressure regulators, click here.

Pneumatic lubricator selection

Pneumatic lubricator

Figure 4: Pneumatic lubricator

Lubricators reduce the internal friction in tools or equipment by releasing a controlled mist of oil into the compressed air (Figure 4). Knowing the pneumatic component’s need for lubrication will determine the oil type and drip rate. The drip rate is how much oil is released downstream. There are two types of lubricators: oil-fog and micro-fog.

  • Oil-fog supplies 100% of the oil seen in the sight glass downstream as a large droplet. It is designed for short distances and typically just for one component requiring heavy lubrication.
  • Micro-fog supplies roughly 10% of the oil seen in the sight glass downstream as a mist (< 2 µm). It is designed for long distances and multiple components.

Lubricators will require maintenance to re-fill the oil reservoir when it becomes low and can be monitored through the sight glass or a window located on the housing. Lubricators also require a pressure differential to make the oil drip, therefore, they create a pressure drop at the outlet. This needs to be taken into account to ensure the proper pressure reaches the end component. This means that air will not be lubricated if the system is off, which allows for no oil waste. It should be noted that many pneumatic components are self-lubricating and don’t require any additional lubrication.

Additional information

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