The 6 Most Common Compressed Air Drying Methods

Water is a challenge in every air compressor system. As air is compressed, water is brought into the air stream. During cooling, that water condenses and is mixed with the compressed air that’s delivered to your tool or application. Some water is okay for most applications but too much water can be a problem. That’s where air drying comes in.

There are six common ways of removing or reducing the amount of water in the air stream. The most common compressed air drying methods include:

  • Aftercooler
    • Air-cooled versions
    • Water Cooled Versions
  • Storage Tank Cooling
  • Refrigerant
  • Deliquescent / Absorption Drying
  • Regenerative / Adsorption Drying
    • Dual Tower Regenerative Desiccant Air Dryers
  • Membrane Type Dryer

Each of these air drying methods is unique, with its own benefits and disadvantages. In this article, we will explain each of the common air drying methods in more detail.

Aftercooler Method

A heat transfer will occur between two bodies of different temperature until temperature equilibrium is reached. This transfer of heat can take place in three different ways and, generally, these take place simultaneously:

  1. Conduction
  2. Convection
  3. Radiation

Aftercoolers use this principle to balance the temperature of compressed air with atmospheric air, and some drying also occurs within the process.

An aftercooler is a heat exchanger used to cool compressed air and minimize moisture within the system. Reduced compressed air temperatures cause water and oil droplets to precipitate out of the air, and these liquid contaminants are typically collected and drained off with a moisture separation device and drain trap (either mechanical or timed).

mechanical float-type drain trap

Figure 1. Typical mechanical float-type drain trap

Typical electrically timed drain trap

Figure 2. Typical electrically timed drain trap

The aftercooler should be located as close as possible to the compressor outlet.

Air-Cooled Aftercoolers

Air AfterCooler – 70 CFM

Figure 3: VMAC’s Air-Aftercooler

The air-cooled aftercooler looks very much like a car radiator, and acts like one as well. However, rather than coolant filling the interior tubes, the hot compressed air enters the bottom of the air-cooled aftercooler and tube system, discharging through the upper discharge port into a moisture separator. Some aftercoolers use electrical powered 12V or 24V fans to push air through the system. The tubes have fins, or metal plates, between them to increase their surface area and dissipate the heat more effectively.

As heat from the compressed air transfers to the cooler atmospheric air, some of the heat of compression is removed from the compressed air and carried away.

Water-Cooled Aftercoolers

Water-cooled after-coolers do the exact same thing as air-cooled aftercoolers, only with much more control of the discharge air temperatures. The primary difference between air-cooled and water-cooled after-coolers is that there is a flow of liquid coolant flowing in a shell and tube or a plate-fin design heat exchanger absorbing the heat of compression from the compressed air volume.

Advantages & Disadvantages of Aftercoolers

Advantages

  1. Reduces heat and moisture within the system
  2. Easy to source
  3. Straightforward addition to most compressed air systems
  4. Fan-less systems don’t require electricity
  5. Efficient heat transfer

Disadvantages

  1. Difficult heat recovery
  2. Requires a high volume of water (water-cooled only)

Storage Tank Cooling Method

The storage tank cooling method of drying air uses an air receiver tank to turn some of the moisture that may be present in the air into water droplets as the air comes from the compressor or that may be carried over from the aftercooler.

As soon as air leaving the aftercooler enters the receiver tank, it comes into contact with the cooler steel wall of the tank, which is usually at ambient temperature. At this point, moisture starts to condense out of the compressed air as the air chills.

If the air is stored in the tank for enough time, the temperature of the air in the tank will be the same as the ambient temperature, and no more moisture will condense out. At this point, the air in the receiver tank is 100% saturated at a dewpoint equal to atmospheric temperature, which results in water formation.

It’s important that this water is drained out of the air receiver tank after each use. The storage of condensation and moisture in air receiver tanks leads to the formation of rust and scale on the inside of the tank, which can become loose and get carried down-stream in the outgoing air. The water can also freeze in colder temperatures. This rust, scale, and ice can cause problems of blockage in air-using components and premature blockage of filters.

Advantages & Disadvantages of Storage Tank Cooling Method

Advantages

  1. Air receiver tanks are inexpensive
  2. Air receiver tanks are easy to source
  3. Simple and straightforward

Disadvantages

  1. Air receiver tanks can take up considerable amounts of space
  2. Not the most effective way to cool air
  3. Requires tank to be drained every day it’s used

Refrigeration Drying

Refrigeration drying occurs as part of the refrigeration cooling process, with the two systems working symbiotically.

There are two types of refrigerated air dryers: Cycling and Noncycling. Both types use a refrigeration system to cool the compressed air to a temperature as close to freezing as possible in order to condense out as much water as possible.

Most provide a pressure dew point of 35°F, but some less expensive models with smaller refrigeration systems are rated for the higher dewpoint of 50°F.

The Typical Flow Pattern - The Refrigeration Cycle

Figure 4: The Typical Flow Pattern – The Refrigeration Cycle

In a refrigeration system, hot compressed air enters the air-to-air heat exchanger and flows down the inner tube of a tube-in-tube bundle. The incoming hot air is re-chilled by the air travelling in the outer tube, which has been cooled by the refrigeration section.

As the air cools, water vapor condenses into liquid droplets. The condensed liquid droplets are then removed from the air stream in a separator and automatically discharged to drain by an automatic condensate drain trap. This pre-chilling is done to allow for the use of a smaller refrigeration unit, and increase the efficiency of the dryer package.

The pre-cooled compressed air then enters the air-to-refrigerant heat exchanger, where the heat is removed directly from the compressed air by the refrigeration system down to +35°F.

As the air continues to cool, water vapor again condenses into liquid droplets. The condensed liquid droplets are then removed from the air stream in another separator and automatically discharged to drain by an automatic condensate drain trap.

Finally, the air passes through the secondary side of the air-to-air heat exchanger, where it is re-heated by the incoming hot air. The re-heating of the outgoing air is to prevent downstream pipe sweating, and increasing the effective volume of the air, enabling it to do more work. It also will take longer for a pipe exposed to cool atmospheric temperatures to drop from the re-heated temperature to a point less than +38°F.

Advantages:

  1. Constant dewpoint of +38°F to +50°F (dependent on ISO class)
  2. Low maintenance costs, with no chemical or desiccants to add or replace
  3. No recurring costs other than electricity
  4. No after filter required (a coalescing type prefilter is recommended)

Disadvantages:

  1. Lowest dewpoint available is +35°F but any lower and the air-to-air heat
    exchanger would freeze up
  2. Some dryers have shown a problem with refrigerant leakage

Deliquescent / Absorption Drying

A Typical Deliquescent Type Air Dryer - Absorption Type

Figure 5: A Typical Deliquescent Type Air Dryer – Absorption Type

Another common way to dry air is through absorption. With absorption drying, incoming air enters the vessel near the base and passes through a mechanical separation section. Due to expansion, the free liquids and solids drop to the bottom of the vessel. To some degree, this constitutes a pre-drying of the air.

The air then enters the desiccant bed of deliquescent materials, such as water-soluble salts or shotted urea. These hygroscopic chemicals condense water vapor as they deliquesce or dissolve the liquid.

Absorption occurs until the deliquescent materials are completely consumed, at which time, they must be replaced.

Advantages:

  1. Low initial cost
  2. No electrical hook-up
  3. No moving parts
  4. Simple operation

Disadvantages:

  1. Dewpoint suppression is between 20°F-30°F (on average)
  2. Deliquescent material must be added to or replaced as it absorbs and melts
  3. Downtime required to replace deliquescent material
  4. Ecological problem of disposing of the dissolved deliquescent material
  5. Cost of replacement deliquescent and of disposal of dissolved deliquescent
    material
  6. Carryover of corrosive deliquescent materials into the downstream piping network
    and air using components
  7. Parts of the deliquescent materials can solidify in the bed, causing channels for
    the air to by-pass most of the drying material, which reduces the dryer’s performance

Regenerative / Adsorption Drying

Desiccant Air Dryer

Desiccant dryers lower the dewpoint of compressed air by adsorbing water vapor onto the surface of a desiccant. The three basic types of desiccant used in dual tower regenerative air dryers are:

  1. Activated Alumina
  2. Silica Gel
  3. Molecular Sieve

The process of adsorption begins as the water vapor, which is more highly concentrated in the compressed air stream, moves into an area of lower water vapor concentration in the pores of the desiccant.

Once inside the pores, a natural attraction of the vapor molecules to the solid surface of the desiccant causes water vapor molecules to build up on the surface of the desiccant. As enough molecules gather, vapor changes phase and becomes a liquid. The process continues as long as the concentration of water vapor in the air is greater than the concentration in the desiccant pores.

The water remains on the surface of the desiccant until it is stripped off. This stripping is called reactivating or regenerating the desiccant. By doing this, the desiccant may be used again and again.

Dual tower desiccant dryers

Figure 6: Dual Tower Desiccant Air Dryer Diagram

Dual Tower Desiccant Air Dryers

Dual tower desiccant air dryers go by many names, including pressure swing, regenerative, and instrument air dryers. Both heated and heatless models are available. Despite the varied terminology, all desiccant dryers offer a continuous supply of dry compressed air by using two identical towers that each contain a bed of desiccant beads.

While one tower is on stream drying the compressed air, the other tower is off stream so the desiccant in that tower can be regenerated. The regeneration of the desiccant bed is accomplished by expanding some of the dried air to near atmospheric pressure and directing it across the wet desiccant bed. This swing in pressure produces expanded air, called purge air, with a very low water vapor concentration.

Imagine that the air being used for the purge flow is 80 °F and has a dewpoint of -40°F at 100 psig. This purge air is then expanded from 100 psig to a couple of pounds pressure, heated to a temperature of between 350-600 °F, and passed counter currently through the wet desiccant bed. The moisture holding capability of this superheated, dry expanded air is extremely high.

The vapor pressure of the hot air is so low in comparison to that of the desiccant that the moisture moves from the area of higher vapor pressure (the desiccant) to that of the lower vapor pressure (the hot purge air).The purge air stream then carries the water vapor out of the dryer.

Dual tower desiccant air dryers are typically used to dry instrument air and process air, as well as air in applications where airlines are exposed to low ambient temperatures, below 32°F, and in other critical applications. Typical dewpoints produced by these types of dryers are -40°F to -100°F, although lower dewpoints are possible.

Advantages & Disadvantages of Desiccant Air Dryers

Advantages

  1. Can operate a very low dewpoint in below freezing temperatures
  2. Delivers extremely dry air that meets ISO Quality Classes 1, 2, & 3

Disadvantages

  1. High purchasing costs
  2. High operation costs
  3. Ongoing maintenance costs

Membrane Type Air Dryers

membrane dryer

The membrane dryer operates on the principal of selective permeation through a membrane.

As the compressed air passes through a bundle of tiny hollow (polysulfone) membrane fibers, water vapor and a portion of the compressed air flow diffuses through the semi permeable membrane walls while the dried air continues downstream.

The water vapor which has been separated from the compressed air by the differential gas pressure on the inside and outside of the hollow fibers, is purged out of the housing by the sweep air (purge air).

The membrane dryer must be used only with clean, oil free air. It must have a coalescing prefilter installed ahead of the dryer to remove any liquid water, oil and aerosol contaminants from the compressed air stream, as these would block the permeation of the fibers, reducing the performance of the dryer.

These dryers are point-of-use dryers and are sized for low capacities compared to other dryer types. The membrane dryer can be connected in parallel to increase the capacity beyond that of the single dryer.

Advantages & Disadvantages of Membrane-Type Dryers

Advantages

  1. There are no moving parts
  2. There are no consumables to replace
  3. They require no external power source
  4. They install directly in the pipeline
  5. They can operate in severe environments, such as high or low temperatures or corrosive and explosive atmospheres
  6. They operate continuously without the need for adjustment or maintenance (other than prefilter maintenance)
  7. Dewpoint suppression range is between +40°F and -40°F

Disadvantages

  1. Some models require (consume) about 15-20% of the purge air
  2. Membrane dryers reduce the oxygen content of the compressed air and cannot be used in breathing air applications

Additional Resources

You may also be interested in the following resources:

What is an FRL – Filter Regulator Lubricator

Air leaving a compressor is hot, dirty, and wet – which can damage and shorten the life of downstream equipment, such as valves and cylinders. Before this air can be used, it needs to be cleaned and lubricated. That’s where an FRL comes in! An FRL combines a filter, regulator, and lubricator into one component to keep air compressor systems in optimal working condition.

FRL Components

An FRL is comprised of three primary components:

  • Airline filter
  • Pressure regulator
  • Lubricator

Each of these individual components has its own role, supporting the larger air compressor system. We will explain more about these roles in the following sections.

Airline Filter

An airline filter cleans compressed air. It strains the air, traps solid particles (dust, dirt, rust) and separates liquids (water, oil) entrained in the compressed air. Filters are installed in the air line upstream of regulators, lubricators, directional control valves, and air driven devices such as cylinders and air motors.

Filter Regulator Lubricator

FRL System

Because airline filters remove contaminants from pneumatic systems, they prevent damage to equipment and reduce production losses due to contaminant-related downtime. Downtime in an industrial plant is expensive; often it is the result of a contaminated and poorly maintained compressed air system.

Selecting the proper size of filter for any application should be done by determining the maximum allowable pressure drop, which can be caused by the filter. The pressure drop can be determined by referring to flow curves provided by the manufacturer.

Types of Air Filters

There are three general types of air filters:

  • General purpose
  • Coalescing (oil removal)
  • Vapor removal

General Purpose, are used to remove water and particles, while Coalescing filters remove oil, and Vapor Removal filters remove oil vapor and odor.

Pressure regulators

Pressure regulators reduce and control air pressure in compressed air systems, including rotary screw air compressors. Regulators are also frequently referred to as PRVs (pressure reducing valves).

Optimally, a pressure regulator maintains a constant output pressure regardless of variations in the input pressure and downstream flow requirements. In practice, output pressure is influenced to some degree by variations in primary pressure and flow.

Pressure regulators are used to control pressure to:

  • Air tools
  • Blow guns
  • Air gauging equipment
  • Air cylinders
  • Air bearings
  • Air motors
  • Spraying devices
  • Fluidic systems
  • Air logic valves
  • Aerosol lubrication system
  • Most other fluid power applications

General purpose regulators are available in relieving or non-relieving types. Relieving regulators can be adjusted from a high pressure to a low pressure. Even in a dead-end situation, relieving regulators will allow the excess downstream pressure to be exhausted. This causes a loud hissing sound which is perfectly normal.

Non-relieving regulators that are similarly adjusted will not allow the downstream pressure to escape. Instead, the trapped air will need to be released in some other way—for example, by operating a downstream valve.

Downstream equipment flow and pressure requirements must be determined to properly size the correct regulator for the application.

Lubricator

A lubricator adds controlled quantities of tool oil into a compressed air system to reduce the friction of moving components. Most air tools, cylinders, valves, air motors, and other air driven equipment require lubrication to extend their useful life.

The use of an airline lubricator solves the problems of too much or too little lubrication that arise with conventional lubrication methods such as a grease gun or oil. Airline lubricators also supply the right kind of lubricant for the tools being used.

Once the lubricator is adjusted, an accurately metered quantity of lubricant is supplied to the air-operated equipment and the only maintenance required is a periodic refill of the lubricator reservoir.

Adding lubrication to a system also “washes away” compressor oils that travel through the system in vapor form. Mineral oils added to the system prevent synthetic compressor oil build-up on system components. When lubricators are not used in a system, a coalescing filter should be installed to remove compressor oil aerosols.

Lubricators are sized by downstream flow requirements. An analysis of air flow use must be made. After determining how much air flow is needed, a lubricator can be chosen. Manufacturers’ curves will be similar to the one shown.

Types of Airline Lubricators

Airline lubricators come in one of two types:

  • Oil-Fog
  • Micro-Fog

Oil-Fog airline lubricators are used for heavy applications such as single tools, cylinders and valves, while Micro-Fog lubricators are used for multiple applications, several cylinders or valves.

In oil-fog lubricators, all the oil droplets visible in the sight dome are added directly into the air flow. This results in relatively large oil droplets passing downstream. In micro-fog lubricators, the oil droplets visible in the sight dome are atomized and collected in the area above the oil in the bowl. The smaller, lighter particles are drawn into the air flow and pass downstream. As a result, typically only 10% of the visible oil drops in the sight dome is passed downstream.

Choosing The Right FRL For Compressed Air Systems

Compressed air is clean, readily available and simple-to-use, but it can be the most expensive form of energy in your application. Unregulated or improper pressure settings can result in increased compressed air demand, which results in increased energy consumption.

Excessive pressure can also increase equipment wear, resulting in higher maintenance costs and shorter tool life. A rule of thumb states that every 2-psig increase in operating pressure adds an additional 1% to compression energy cost.

Point-of-use FRLs (filter, regulator and lubricators) are needed to ensure that every tool or process is receiving a clean, lubricated supply of compressed air at the proper pressure to provide peak performance.

Choosing A Filter For Compressed Air

Reliability is one of the strongest reasons to use compressed air, and proper filtration is the key to maximizing reliability and longevity. Compressed air can carry condensed water, oil carryover from compressors, solid impurities (pipe scale and rust) generated within the pipelines, and other wear particles from the ambient air. These contaminants can cause problems at every point of use, and should be removed by installing suitable filters.

Contaminant particle size is measured in micrometers (µm), which each represents one-millionth of a meter or 0.000039 of an inch. Filters are rated according to the minimum particle size that their elements will trap. Although filters rated at 40 to 60 µm are adequate for protecting most industrial applications, many point-of-use filters are rated at 5 µm. Note that finer ratings increase the pressure drop through the filter, which equates to higher energy cost to compress the air.

In addition, finer filters clog more rapidly, also increasing pressure drop. (In other words, while filters finer than necessary do no harm to downstream components, they will have a negative impact on air system operating cost.)

 point-of-use filters

Point of use filter

Many filter manufacturers will define the expected pressure loss and dirt holding capacity, using curves related to pressure and flow. Therefore, particle-removal filters should be selected based on acceptable pressure drop and pipe-connection size.

A typical pressure drop through such filters would be between 1 and 5 psig. A filter with larger body size will produce less initial pressure loss and provide longer operating life than a smaller size filter with the same removal ratings.

Most point-of-use filters claim to remove condensed water, typically via a form of cyclone separator at their inlet end. The water-removal efficiency of such filters is very dependent on the incoming air velocity. Therefore, these filters must be matched to the intended airflow, rather than acceptable pressure drop.

If the filter is intended to remove moisture, an integral automatic float-type drain should be provided to periodically remove accumulated liquids from the filter bowl. Generally, such filters have transparent polycarbonate bowls, which allow easy visual inspection of the sump level.

Numerous chemicals can attack this plastic material and it only performs well at pressures below 150 psig and temperatures between 40° and 120° F. A metal bowl may be required when the filter could be subjected to conditions outside those limits, as well as when synthetic compressor lubricants, which often contain chemicals that are harmful to polycarbonate, are present.

Coalescing-type filters,

Coalescing filter

Coalescing Filters

Most oil entrained in a compressed air stream, as well as some of the condensed water, will be in the form of mists or aerosols that can pass through the openings in standard airline filters. Air for instruments, spray painting, and bulk-material conveying frequently requires the removal of such droplets. Coalescing-type filters will accomplish this job.

Aerosol carryover through such filters is commonly stated as parts per million (ppm) of oil vs. air by weight and will range from 1 to as little as 0.01 ppm. Coalescing filters are often rated to remove aerosols that are substantially smaller than the nominal size of the smallest solid particle that would be captured. Some models offer dual-stage filtration; the first removes solid particulates to protect the coalescing element in the second stage.

Because all coalescing filters create a greater restriction to the airflow, pressure losses will be higher than those of conventional compressed air filters. Coalescing filters have an initial (or dry) pressure drop and a working (or saturated) pressure drop, both based on pressure and flow rate. The effective removal efficiency of such filters depends greatly on the air velocity passing through the filter assembly.

Therefore, choose a coalescing filter based on acceptable oil carryover, expected airflow rate, and pipe-connection size. A coalescing filter rated at 0.1 ppm will typically have a clean, wetted pressure drop between 2 and 5 psig, while a high-efficiency filter rated at 0.01 ppm can cause as much as 10 psig drop once it becomes wetted or fully saturated during service.

Flow in scfm

High efficiency filter pressure by flow

Selecting The Right Pressure Regulators

Once a minimum suitable operating pressure has been determined for any compressed air application, it is essential to supply the air at a constant pressure, regardless of upstream flow and pressure fluctuations. Thus, it is critical to install the proper regulator or pressure-reducing valve in the airline.

Air regulators are special valves that reduce supply pressure to the level required for efficient operation of downstream pneumatic equipment. A filter to protect the regulator’s internal passages from damage should always be installed upstream from it.

Poppet-Style Valves

There are several types of air regulators. The simplest type uses an unbalanced-poppet-style valve. This design incorporates an adjustment spring, does not have a separate diaphragm chamber, and is non-relieving. Turning the adjustment screw compresses the spring, which forces the diaphragm to move, thus pushing a poppet to uncover an orifice.

As pressure rises downstream, it acts on the underside of the diaphragm, balancing against the force of the spring. The poppet throttles the orifice opening to restrict flow – and produce the desired downstream pressure. A spring under the poppet assures that the valve closes completely when no flow exists. This is the least expensive type air regulator.

Pressure regulators

Regulator with diaphragm chamber

Diaphragm Chambers

Larger, more expensive regulators, incorporate a separate diaphragm chamber, which has an aspirator tube exposed to the output pressure. Segregating the diaphragm from the main airflow minimizes its abrasive effects and extends the life of the valve.

As flow through this regulator increases, the aspirator tube creates a slightly lower pressure in the diaphragm chamber. The diaphragm deflects downward and opens the orifice without significantly reducing the output pressure. The effect is the same as increasing the adjustment setting. Thus, this style regulator has minimal drop (output pressure decay) as supply pressure varies. The table below compares how that variance occurs with a small and a large diaphragm.

The larger diaphragms in these regulators improve response and sensitivity. As discharge flow through the regulator is increased over its entire range, output pressure drops. Thus, it is important to set the regulator’s desired output pressure under normal flow conditions.

 

Supply Pressure in PSI

Supply pressure in small vs large diaphragms

 

Flow in scfm

Flow in scfm of small vs large diaphragms

Balanced Poppet & Precision Regulators

Another type of regulator incorporates a balanced poppet, but otherwise has the same general construction as the separate diaphragm version. It has a significantly larger orifice to allow for greater airflow. To maintain good stability, the poppet is pressure-balanced. Thus, the effects of output pressure fluctuations cancel out, which improves sensitivity and response, and reduces droop.

Finally, precision regulators often employ several isolated diaphragms acting against flapper valves and nozzles in a balancing principle and are normally manufactured in limited flow capacities with smaller connection ports.

Considerations When Selecting Regulators

Selecting the best type of regulator for a specific application first requires a choice among these styles. Mini-regulators are commonly the direct-acting, non-relieving type, while most standard regulators fall within the self-relieving, separate-diaphragm-chamber style.

The next consideration becomes primary (unregulated supply) pressure versus desired secondary (output) pressure.

Finally, desired airflow rate must be selected. Adjusting screws are normally offered in two styles: tamper resistant, locking Tee type or push-lock, plastic knob type. The first is best when a fixed operating pressure will be set once and left alone. The adjustable knob style (quite common on modular FRLs) is the correct choice for general use, where the operating pressure can be easily adjusted without tools. Regulators also are defined by body size (orifice flow rating) and connection size.

Although several models may appear to be acceptable for any given airflow and pressure, a larger body size regulator will produce better setting sensitivity and less droop than a smaller body model under the same set of operating conditions.

An output pressure gauge is essential, although many manufacturers frequently offer it only as an option. Mounting brackets are another useful option.

Choosing The Best Airline Lubricator

Airline Lubricators

Airline lubricator

Many pneumatic system components and almost all pneumatic tools perform better when lubricated with oil. Injecting an oil mist into the air-stream which powers them can continuously lubricate valves, cylinders, and air motors for proper operation and long service life.

Locating the lubricator last in the pipeline is important to ensure that the correct amount of lubrication reaches each device. Too little oil can allow excessive wear and cause premature failure. Excessive oil in the pipeline is wasteful and can become a contaminant in the ambient area as it is carried out of tools and valves by the air exhaust.

Intermittent lubrication may be the worst condition of all because the oil film can dry out and form sludge or varnish on the internal surfaces of the equipment.

Airline lubricators meter oil from a reservoir into the moving air-stream. As high-velocity air passes through a venturi, it draws the oil up and through a capillary, then drips it into the air-stream.

The moving air breaks up the oil into a mist (small droplets) or fog (larger droplets), which is then carried downstream into the air-powered device. In a typical lubricator, all of the air passes through the venturi during low-flow conditions.

Under higher flow conditions, a spring-loaded bypass valve opens to direct the excess flow around the venturi to a point downstream where it rejoins the lubricated flow. A manual adjusting valve sets the oil drip-rate and a sight glass enables the operator to monitor the output. A fill plug provides access to refill the reservoir, which typically is made from polycarbonate. The same precautions about polycarbonate apply to lubricators as they do to airline filters.

Pressure drop in PSI

Lubricator pressure and flow

Lubricators typically have a larger flow range than an equivalent size regulator or filter, but their pressure drop increases quite rapidly as flow increases.

The acceptable pressure loss for a lubricator is normally considered to be 3 to 7 psig. Lubricators are generally selected based on pipe connection size, oil reservoir capacity, and acceptable pressure loss versus flow rate (many manufacturers publish a minimum flow rate at which the venturi will function properly).

Remember to account for this added downstream pressure loss when setting the pressure regulator. Set it at desired use pressure plus lubricator loss (drop).

Modular & Combination FRL Units

Modular or combination units

Combination FRL unit

Manufacturers frequently preassemble filters, regulators, and lubricators to form combination units. They are packaged together as common body sizes with common connection port sizes. Interconnections may be via threaded nipples or modular face connectors.

The modular connectors allow easy removal of components for servicing or cleaning. In addition, some manufacturers combine filters and regulators in stacked assemblies where the filter head becomes the regulator body. The components share common inlet and outlet connections, which makes the assembly very compact.

filter-regulator-lubricator

Individual pressure regulator

Such packaged units, whether F-R only or complete F-R-L, are practical choices for most industrial applications. The selection criteria are the same as with any of the individual components, except that the combined pressure and flow performance becomes the only consideration.

Note that when critical requirements dictate the use of specialty filters or precision regulators, the assembly probably must be made up of individual selections and connected with pipe nipples.

VMAC Air Innovated

ACFM (Actual Cubic Feet per Minute) vs. SCFM (Standard Cubic Feet per Minute)

The air compressor industry loves to use acronyms, especially when measuring airflow and air consumption. Two common acronyms, representing measurements, are ACFM and SCFM.

CFM—or Cubic Feet per Minute—is an important metrics when choosing an air compressor and related pneumatic equipment. Pneumatic tools and equipment require a specific minimum air mass, or CFM, to perform properly on the job site.

But what exactly does it mean when manufacturers use ACFM or SCFM to perform properly on the job site?

What is ACFM?

ACFM (Actual Cubic Feet per Minute) may have different definitions depending on the industry.  VMAC defines ACFM as the true air mass flow given a certain set of real-life conditions. We will simulate a real life environment and then measure the CFM based on the actual output of air, resulting in ACFM.

But ACFM is impacted by atmospheric conditions and the surrounding environments. For example, an air compressor on a mountain top is likely to have lower output than that same air compressor will have at ocean level.

What is SCFM?

SCFM (Standard Cubic Feet per Minute) measures air output, like ACFM, but uses a standard that takes atmospheric conditions into account.

SCFM is a set of specific parameters determined by the American Society of Mechanical Engineers (ASME) that are recognized across many industries. These SCFM calculations are based on atmospheric conditions (“standard conditions”) to measure air mass flow from an air compressor.

SCFM “standard conditions” include:

  • atmospheric pressure at sea-level of 14.7 PSIA (760 mmHg),
  • relative humidity of 36%, and
  • ambient temperature of 68°F (19°C).

After completing the calculations using these conditions, the maximum SCFM output of the air compressor is revealed.

SCFM is the only way to compare “apples to apples”, or air compressor to air compressor, as operating conditions may otherwise vary depending on where the air compressor air mass flow is being measured. VMAC defines SCFM as the air mass flow generated at “standard conditions”.

Differences Between ACFM & SCFM

jack hammer

At “standard conditions”, with no efficiency losses, SCFM equals ACFM.  Where inlet conditions vary from “standard conditions”, consideration may be necessary to ensure the specified air compressor has enough power to generate adequate air mass flow for the tool to perform properly on the job site.

ACFM demand by a tool may be higher if any one of the following conditions is different from standard conditions:

  • atmospheric pressure is lower (elevation)
  • humidity is higher
  • temperature is higher

Another way of thinking about this is the air compressor needs to work harder as the job site drifts away from “standard conditions”.  A more powerful air compressor (with higher SCFM rating) may be required to generate adequate ACFM for the pneumatic tool to perform properly on the job site.

Quick Calculations:

  • For every 1000 ft (305 m) of elevation increase over “standard conditions”, ACFM demand increases by approximately 5%.
  • For every 20oF (11.1oC) of ambient temperature increase over “standard conditions”, ACFM demand increases by approximately 5%.
  • For every 20% of humidity increase over “standard conditions”, ACFM demand increases by approximately .5%.

Example Calculation:

A 1” impact gun may have a minimum air mass flow requirement of 45 CFM.  On the job site in Ft McMurray, Alberta at an elevation of 1,211 ft (369 m) on June 22, 2011 at 2:00PM, atmospheric pressure is 14.2 PSIA (732 mmHg), humidity is 24%, and temperature is 84oF (27oC).   For an air compressor to generate 45 ACFM in these conditions, it actually needs to have an SCFM rating of approximately 49 SCFM.

Why Does ACFM vs. SCFM Matter?

You need to ensure your air compressor system produces enough air to properly power your tools. If the environment you work in impacts air production, SCFM ratings may not perfectly reflect your real-world needs. Unless you are only using your air compressor on the beach on a cool spring day, add a buffer when specifying your equipment.

VMAC Air Innovated

Commercial Van Education

Interest in commercial vans to replace traditional service trucks continues to grow. Sales figures provided by the NTEA (National Truck Equipment Association) show it’s a trend that is not fading. Growth has been sustained over about a 5-year period, and the reasons for this are clear. Continue reading “Commercial Van Education”

With Ogura’s help, VMAC develops tiny 30CFM air compressor and discovers new market

VMAC UNDERHOOD 30 CFM Air Compressor

Ogura’s new small size/high torque electromagnetic clutch helps VMAC’s aftermarket UNDERHOOD™ LITE air compressor meet performance and cost reduction goals previously unobtainable.

Today’s commercial van manufacturers are changing the game by delivering new Euro style vans to North America. These new platforms boost fuel efficiency and increase cargo space dramatically. Ford’s 3.7 L Transit, Mercedes Benz’s 3.0L Sprinter, and the Ram 3.6L ProMaster are but three of the new entrees causing shakeups in the mobile service industry.

While these vehicles offer state of the art engines, reduced emissions, and roomy vehicle platforms, they have drastically reduced the amount of available under hood space usually allocated for engine driven aftermarket components such as; air compressors, secondary alternators and hydraulic systems.  Generally, mobile service businesses and municipalities buy these vehicles and outfit them with engine driven accessory systems for the many important tasks they do every day.

Continue reading “With Ogura’s help, VMAC develops tiny 30CFM air compressor and discovers new market”