What Is An Air Receiver Tank & What Does It Do?

A300047-A 10 gallon air receiver tank

10-Gallon Air Receiver Tank w/ Mounting Fee

An air receiver tank is a metal tank that stores compressed air until it is required. Air receiver tanks can vary in shape and in size, depending on the application. Air receiver tanks on service vehicles are typically 30 gallons, but still range from 6 to 50 gallons.

Some air compressors, such as reciprocating air compressors, require an air receiver tank to operate. But even air compressors that don’t need an air receiver tank can benefit from the installation of one.

What Does An Air Receiver Tank Do?

Air receiver tanks serve many important functions and roles within an air compressor system. An air receiver tank:

  • Dampens pulsations from the discharge line of a reciprocating compressor, resulting in an essentially steady flow of air in the system.
  • Serves as an air reservoir to take care of sudden or unusually heavy demands for air that’s in excess of the compressor’s designed capacity.
  • Prevents the excessive cycling of a compressor.
  • Knocks out solid dirt and particulate matter that may have passed through the compressor inlet filter or may be the result of compressor wear.
  • Precipitates out contaminants and oil carry-over from the compressor oil that might get into the compressor discharge
  • Helps cool the compressed air and precipitates out moisture that inevitably results from air compression

Pulsation Damping

During the compression of air in a reciprocating compressor, air is delivered in pulses through the discharge line. This pulsation is caused by the alternating suction and compression stroke of these types of compressors.

Adding an air receiver tank dampens these pulses and allows a smoother delivery of air to the tool or piece of equipment being used. Pulsation dampening also helps protect hoses and components from damage caused by pressure spikes.

Air Reservoir

Air receiver tanks provide a reservoir of compressed air. An air receiver tank is capable of storing compressed air to be used once the compressor has been turned off, and to offset sudden, heavy demands of air.

If sized appropriately, an air receiver tank may also allow the use of a smaller compressor in low duty-cycle applications requiring higher air flow than the compressor can continuously deliver. For example, a low CFM rotary screw air compressor that can’t quite power a 1” impact gun continuously may be able to do so with a small air receiver tank

Reduce Compressor Cycling

35 Gallon Air Receiver Tank

35-gallon air receiver wing tank

As mentioned above, the tank can store air and act as a buffer.  This also allows the compressor to cycle on and off less frequently, which can reduce wear and tear and reduce energy consumption. Care must be taken to ensure that the compressor system is rated and able to run long enough to fill the size of tank chosen without overheating or causing accelerated wear.

Particulate and dirt removal

During everyday air compressor operation, dirt, wear particles, or other foreign matter may bypass the air filter or otherwise find their way into the compressed air stream. This debris in the air stream can then cause blockages, premature contamination of filters, and excessive wear on tools and equipment.

An air receiver tank helps remove some of these particulates and dirt from the compressed air system, as some of this material will naturally fall to the bottom of the air receiver tank before the air reaches the tool or equipment that’s in use.

Moisture Removal

Atmospheric air typically contains moisture that is drawn into the compressor during its intake cycle. The moisture holding ability of air naturally increases as the temperature and pressure of compressed air temperature rises. Hot, compressed air typically holds moisture in a vapor state, but that moisture will condense into liquid form as the air cools past its saturation point.

Air receiver tanks are typically uninsulated, which means that hot compressed air enters the receiver tank and immediately starts to cool by transferring heat to the environment through the walls of the tank.

Without an air receiver tank or aftercooler, this cooling happens in an airline and is commonly seen as liquid water coming out of the tools or equipment. When using an air receiver tank, much of this liquid is collects in the bottom of the tank, which can easily be drained at the end of each working day.

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How To Size An Air Receiver Tank

Many air compressor applications can benefit from the installation of one or more air receiver tanks. An air receiver tank increases the amount of air available on demand, allowing for higher duty cycles and more powerful applications.

Air receiver tanks are sized in gallons, and can range from small 5- and 10-gallon tanks to massive tanks that hold thousands of gallons of air. The ideal size of an air receiver tank will depend on the type of air compressor and the application.

Air Receiver Tanks For Portable Air Compressors

Tanks for Reciprocating Air Compressors

Reciprocating air compressors use an air receiver tank to store air and eliminate pulsation before it can be used. Once the tank is filled with enough air, the tool or equipment can run. In many applications, using the tool will drain the tank, and operators will need to wait for it to fill back up before more air can be used. Properly sizing the air receiver tank that’s used with a reciprocating air compressor can help reduce interruptions and time wasted waiting for the tank to refill.

A simple and straightforward rule for sizing an air receiver tank for a reciprocating air compressor is to take the tool with the highest CFM requirement (at the required PSI), multiply that CFM requirement by 1.25 or 1.5, and then round up to the closest gallon size.

CFM Requirement1.25 Multiply1.5 MultiplySuggested Tank Size
20253030 gallon
40506050-60 gallon
6581.2597.590-100 gallon
80100120100-120 gallon

While these calculations may not completely eliminate the waiting time between tank fills, it will help minimize them.

Tanks for Rotary Screw Air Compressors

It can be trickier to size an air receiver tank for a rotary screw air compressor, as many applications don’t require an air tank at all. Rotary screw air compressors are designed to supply a continuous stream of air without interruption and pulsation. Therefore, if your tool requires less CFM than the air compressor produces, an air receiver tank shouldn’t be required.

However, smart operators may choose to use an air receiver tank to give their compressor a little boost for higher CFM tools. For example, if an operator routinely uses a 1” impact wrench that requires 40 CFM, but only has a 30 CFM air compressor, he may choose to add a 12-gallon air receiver tank to compensate for the difference. By the time the air receiver tank is empty, the task will be complete. Operators can sometimes save money or “make do” with a smaller system using this savvy strategy.

Air Receiver Tanks For Stationary Air Compressors

Properly sizing an air receiver tank for custom stationary applications is more complex and should typically be done by a qualified engineer. These air receiver tanks should be sized according to the volume and pressure variations in air consumption (ie: demand), air compressor size, pipe or hose size and length, and the control system strategy (ie: modulation or on-off control.)

A commonly used formula to find a receiver size is:

t = V (p1 – p2) / C pa


  • V = volume of the receiver tank (cu ft)
  • t = time for the receiver to go from upper to lower pressure limits (min)
  • C = free air needed (scfm)
  • pa= atmosphere pressure (14.7 psia)
  • p1 = maximum tank pressure (psia)
  • p2 = minimum tank pressure (psia)

Formula Sizing Example

Let’s look at an example, using an air compressor system with the following specifications:

  • mean air consumption = 20 cfm,
  • maximum tank pressure = 175 psi,
  • minimum tank pressure = 90 psi, and
  • time the tool will run = 1 minute

The approximate ideal volume of the receiver tank can be calculated by modifying the sizing formula to:

V = t C pa / (p1 – p2)
= (1 minute) (20 cfm) (14.7 psi) / ((175 psi) – (90 psi))
= 3.46 ft3
= 25.9 gallons

However, this formula tends to work best for large reciprocating air compressor systems.

Calculating Maximum Air Consumption

Identifying the maximum consumption of an air compressor system is critical when sizing an air receiver tank. Ideally, the air receiver tank will provide enough air to meet or exceed maximum consumption.

In the t = V (p1 – p2) / C pa formula, maximum air consumption is measured in SCFM and represented by “C”.

To calculate the maximum consumption in the system, summarize the air demand of each air tool or consumer that will be used at the same time. The summarized consumption must then be multiplied with a utilization factor for each consuming item.

Utilization Factor

The utilization factor is the way in which a tool is used and how that use affects air flow.

Let’s say you have an air tool like an impact wrench, which is rated by the manufacturer for a consumption of 20 CFM at 100 PSIG. This wrench may be turned on for only 20 seconds at a time to tighten an individual nut to its required torque value.

Initially, the tool will consume the full rated 20 CFM as it tightens the nut against almost no resistance but as the torque rises on the nut, the tool will consume less air until the final torque is achieved. The tool also won’t consume air when it isn’t being used, in between nuts.

The tool’s air consumption under load is not uniform throughout the process of torquing the nut, and the interval between applying the tool between individual nuts varies—this difference in CFM load and time interval becomes the utilization factor.

In other words, just because the tool is rated at 20 CFM, this does not mean that the tool requires the full rated CFM for each full minute nor the full minute to complete the job.

Because of this utilization factor, some air receiver tanks can meet heavy, short time demands of certain equipment at volumes that exceed the supply capabilities of the installed compressor. The minimum receiver capacity for certain applications may also be calculated, but experience and judgment are important at this point.

Pressure Band / Differential

The pressure band (differential) should also be considered when calculating the ideal air receiver tank size.

If the consumption process requires 100 psig and the compressor is set to deliver 100 psig, there is no storage and no buffer. Any increase in demand will result in a tank pressure drop below 100 psig until the compressor responds by increasing the air volume compressed to refill the tank and restore the 100 psig.

If the compressor is set to deliver 110 psig, the difference between 110 psig and 100 psig accounts for the air stored in the receiver.

If the 100 psig demand increases, the tank pressure can drop 10 psig before the minimum set pressure requirement is met. Keep in mind that the discharge piping and hoses also form part of the storage volume.

Pressure and flow controllers can be used after the receiver tank for stabilizing downstream pressure to 100 psig and flattening demand peaks.

When Does Exact Sizing Matter?

Even with the knowledge above, properly sizing an air receiver tank is a complicated and time-consuming process. Operators using straightforward tools and air compressors can default to simple CFM recommendations, and choose a receiver tank using a 1 CFM to 1.25-1.5 gallon ratio. Meanwhile, engineers developing complex and custom systems will need to determine more exact sizing requirements and need to put in the work.

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Compressed Air Aftercoolers

Air AfterCooler – 70 CFMWhat are compressed air aftercoolers and why are they required? Find out everything you need to know about aftercoolers in this article, including the two most common types, why they’re important, and their role within an air compressor system.

What Is An Aftercooler?

An aftercooler is a mechanical heat exchanger designed to remove the heat-of-compression from a compressed air stream and to condition the air so it can be used in air-operated equipment.

A compressed air aftercooler has three primary functions:

  • Cool air discharged from air compressor via a heat exchanger
  • Reduce compressed air moisture level
  • Protect downstream equipment from excessive heat and moisture

Why Are Air Aftercoolers Required?

Regardless of the type of compressor being used, the compressed air discharged from that air compressor is going to be hot. That temperature will vary according to the type of compressor being used.

Typical Compressor Average Outlet Temperatures:

Oil-Injected Rotary Screw        200°F
Oil-Free Rotary Screw              350°F
2-Stage Reciprocating              300°F
Centrifugal                                 225°F

High-temperature air is typically not usable in air-operated equipment, as heat has a detrimental impact on equipment lubrication and sealing materials. Hot air also contains large quantities of moisture vapor which, as it condenses, contributes to rust, scale build-up, washing out of lubricant and possible freezing issues.

Water exists in a vapor state in all atmospheric air (relative humidity) and as the air is drawn into a compressor and pressurized, this moisture is concentrated in each cubic foot. Due to the high temperature of the air, the moisture remains in a vapor state (above the dew point temperature).

The dewpoint is the temperature at which this air becomes saturated at 100% of its capacity to hold water in a vapor state and, with any additional cooling, must release excess moisture as a liquid. A general rule is that for every 20°F rise in temperature the air can hold twice the moisture load in a vapor state above the dewpoint.

Source: Engineering ToolBox / engineeringtoolbox.com

As the compressed air cools this water vapor condenses into a liquid form and is removed from the air stream. As an example, if an aftercooler is not used, a 200 cubic feet per minute (CFM) compressor operating at 100 psig can introduce as much as 45 gallons of water into the compressed air system each day.

Types Of Aftercoolers

The two most common types of aftercoolers are air-cooled and water-cooled.

aftercoolerMost air-cooled aftercoolers are sized to cool the compressed air to within 15°F to 20°F of ambient cooling air temperature (approach temperature). As the compressed air cools, up to 75% of the water vapor present condenses to a liquid and can be removed from the system.

A moisture separator, installed at the discharge of the aftercooler, mechanically removes most of the liquid moisture and solids from the compressed air. Utilizing centrifugal force, and in some cases baffle plates, moisture and solids collect at the bottom of the moisture separator. An automatic drain should be used to remove the moisture and solids. Similar to the air-cooled version, the typical water-cooled approach temperature is between 10°F and 15°F.

In stationary compressor installations, where cooling water is available, water-cooled aftercoolers are often used. There are a few advantages to using water as the cooling media:

  • Water has little seasonal fluctuation in temperature
  • Large volumes of cold water can be used
  • Cold water can efficiently approach the ambient air temperature, which eliminates condensation downstream

Air-Cooled Aftercooler

air-cooled aftercooler

Source: Parker / parker.com

Air-cooled aftercoolers use ambient air to cool the hot compressed air. The compressed air enters the air-cooled aftercooler. The compressed air travels through either the spiral finned tube coil or a plate-fin coil design of the aftercooler while ambient air is forced over the cooler by a motor-driven fan. The cooler, ambient air removes heat from the compressed air. Liquid water forms as the compressed air cools. The moisture is removed by the moisture separator and drain valve.

Belt Guard Air-Cooled Aftercooler


Source: AKG / akgts.com

A belt guard air-cooled aftercooler mounts to the compressor’s v-belt guard. The compressor’s belt pulley has fins designed to force ambient air over the compressor and air-cooled aftercooler. The air passing over the aftercooler facilitates the heat transfer. The pulley also sends air over the compressor helping maintain proper operating temperature.

Water-Cooled Aftercooler


Source: Parker / parker.com

Water-cooled aftercoolers come in different styles. The most common style for compressed air service is a Shell and Tube Heat Exchanger/Aftercooler. This aftercooler consists of a shell with a bundle of tubes fitted inside. Typically, the compressed air flows through the tubes in one direction as water flows through the shell side in the opposite direction (counter-flow). Heat from the compressed air is transferred to the water. Liquid water forms as the compressed air cools. The moisture is removed by the moisture separator and drain valve.

How To Size An Aftercooler

Coolers are usually sized with a CTD (Cold Temperature Difference) of 10°F, 15°F or 20°F. This means that the compressed air temperature at the outlet of the aftercooler will be equal to the cooling medium temperature plus the CTD when sized for the specified inlet air temperature and flow. The lower that temperature needs to be, the larger the aftercooler needs to be.

The required compressed air temperature is determined by other components downstream in the system. It is critical that each individual component’s maximum temperature is determined and considered to discover the true temperature requirements for the aftercooler.

operating-temps air compressor components

Disclaimer: Individual air compressor components may vary from the chart above; always check with the component manufacturer for specs and tolerances, including typical and maximum operating temperatures.

Compressor manufacturers may include integral aftercoolers as a component of the compressor system. Otherwise, a stand-alone or freestanding aftercooler is a separate unit installed downstream of the compressor.

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

Want to learn more about air compressors? Check out our other articles!

The VMAC Diesel Driven Air Compressor’s Helpful Control Box Features & Functions

D60 control box

D60 Control Box

The control box is essentially the brain of the VMAC diesel driven air compressor system. It tells the system what to do and makes decisions based on the programmed settings. The control box is also the communication hub for the air compressor, relaying important information to the operator on an “as needed” basis.
Continue reading “The VMAC Diesel Driven Air Compressor’s Helpful Control Box Features & Functions”

Why does hose size affect my compressor airflow?

It’s important to consider appropriate sizing of all components of your air system.  If you are investing in an air compressor system, restricting the flow anywhere in your system could make it significantly underperform or cost you a lot more in energy costs to run that compressor over its lifetime.

As air travels from the compressor head to your tool it travels through components such as hoses, fittings, valves, and tanks. Each of these will restrict the flow of air in some way depending on the geometry of each component and the magnitude of the flow passing through it.

For example, a long small hose feeding a high air demand tool can result in a high-pressure drop. The result of this will mean either your compressor is working harder and using more power to keep up with your air demands, or—if it can’t keep up—your tool performance will be reduced.  In some cases, where torque or power at the tool is important, you may not be able to complete your work.

Quick calculators or charts can be referred to for calculating the pressure drop in any of your components. The following components should be considered for proper sizing.

  • Hose reels
  • System piping/tubing
  • Filters
  • Regulators
  • Lubricators
  • Quick connect fittings
  • Fittings

Components such as filters will have pressure drop ratings at different flow rates. Be sure to check the documentation and specifications to match them to the system you are installing the components on.

When considering fittings and quick connects, work with your suppliers to make sure they are rated for the maximum pressure your compressor system is rated for and will not cause excessive pressure drop at the required flow rates.

90° fittings like this may restrict airflow

90° fittings like this may restrict airflow

How Fittings Cause Pressure Drops

Pressure drop is due to the restriction created by the pipe or fitting.  Anyone who has tried to breathe through a drinking straw can tell you that trying to force a large flow of air through a small hole can be difficult. This is because the smaller the diameter, the higher the velocity is required for the air to travel through the hole.

Higher velocities result in more friction created. due to boundary layers at the walls of the pipe or fitting creating more losses. With pipes and hoses, the loss is multiplied by the length of the pipe.

It can be surprising how small the flow diameter is in some fittings.  A quick connect fitting is one of the worst culprits.  Next time you are looking at a quick connect, look inside to see how small the actual flow area is.

Calculating Pressure Drop of Fittings

Pressure drop can be calculated for some components and is made even easier by online tools such as this one.  Note that this calculator is for hard pipe as it is a well-defined shape. Flexible hose in actual use typically contains many bends and loops and as such it is not possible to create an accurate generic calculator. While flexible hose will have more losses than a pipe with an identical inside diameter we can still use the pipe loss calculation to get an estimate and see the influence diameter has on pressure loss.

Let’s look at some examples.

To illustrate the dramatic difference pipe/hose diameter makes on pressure loss, let’s use this tool to compare 100ft long pipes with internal diameters of ½”, ¾”, and 1” for 70CFM FAD (free air delivery) of compressed air delivered at 100 PSI gauge pressure (equivalent to 114.7 PSI absolute pressure*) at the upstream hose entrance.

The approximate pressure loss from end to end for the three pipe sizes is:

1″ x 100’: ~1.4 PSI pressure loss

3/4″ x 100’: ~5.7 PSI pressure loss

1/2″ x 100’: ~44 PSI pressure loss

Your compressor would actually have to be operating at ~134 psi gauge pressure† to maintain 100 psi at the tool with the ½” pipe.

Increasing Pressure vs. Increasing Supply Line Size

Increasing the pressure of your compressor to compensate for flow losses can have a dramatic impact on the amount of work your compressor system is doing. Conversely, increasing the size of the supply lines can provide the following benefits:

  • Less fuel/energy used by your compressor
  • Less heat generated by the compressor
  • Longer oil life and service interval
  • Lower noise output from the compressor
  • Improved safety due to lower operating pressures and lower temperatures
  • Lower load on drive system components
  • Less wear and longer life of your compressor

Each restrictive fitting, hose, accessory, bend etc. you add to your system results in cumulative pressure drop and can have negative results on the performance of your tool or equipment.  Recognizing this and planning and sourcing the right sized components will enable your air system to perform better.

As always, keep in mind that formulas and calculators like the one used above are just a guide.  Real life scenarios depend on many factors and each will affect your individual results.  Using larger diameter hose may cost more but it can result in long-term savings and may even allow for a lower pressure or output compressor, saving money up front.

*Absolute pressure is the pressure relative a perfect vacuum.  Gauge pressure is relative to atmospheric pressure. Standard atmospheric pressure is 14.7 PSI so for a calculation, such as this one, that requires the use of absolute pressure, atmospheric pressure (14.7 psi) needs to be added to your gauge pressure.

† Note that it may seem at first glance that the entrance pressure would need to go up by the same pressure as the loss in the pipe from the first calculation but it’s actually slightly less. As the pressure goes up the volume flow and flow velocity goes down for the same mass flow of gas and therefore so does the pressure drop.

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VMAC Direct-Transmission™ Mounted Air Compressor & Multipower System Control Box Features

The control box plays an important role in the Direct-Transmission™ Mounted air compressor and multipower systems (DTM), as it’s used to power the system and communicate with operators and service techs. In addition, the control box monitors the air compressor system on an ongoing basis to ensure its in proper working order.
Continue reading “VMAC Direct-Transmission™ Mounted Air Compressor & Multipower System Control Box Features”

Pressure Relief Valves For Air Compressors

Pressure relief valves, or safety valves, are a simple but critical part in any air compressor system. Pressure relief valves are used to control and limit the pressure build-up in a system. If pressure exceeds the amount allowed by the pressure relief valve, the pressure relief valve will automatically open and release air until the pressure is reduced.

Why Do Pressure Relief Valves Matter?


Image Source: cdivalve.com

Pressure relief valves keep everyone safe. If pressure within an air compressor system or air receiver tank gets too high, one or more components could explode. Pressure relief valves are used to prevent this from occurring.

The rated pressure of the pressure relief valve must not exceed the maximum allowable working pressure (MAWP) marked on the air pressure vessel. This requirement ensures the pressure relief valve will always open before the vessel reaches its maximum pressure tolerance.

In addition, the minimum relieving capacity of the pressure relief device must meet the requirements of the American Society of Mechanical Engineers (ASME) Code. ASME is the international leader in developing and revising codes associated with mechanical engineering.

How Do Pressure Relief Valves Work?

Pressure relief valves for air compressor systems are simple, spring-loaded mechanisms. When the inlet pressure force is greater than the spring load, the safety valve opens in proportion to the increase in pressure and allows air to “leak out” as needed.

Pressure relief valves for compressed air applications are direct-acting, which means they automatically react if the pressure gets too high. If excessive pressurization occurs, a disc seal is moved up by system pressure against a spring, which is holding the valve closed. If the compressed air force exceeds the force exerted by the spring, the valve disc is lifted off the valve seat and the valve discharges the compressed air to the atmosphere.

In accordance with the requirements of the ASME relief valve standard, the full discharge capacity of the valve typically will be achieved when the system pressure climbs to no more than 10% above the set pressure of the valve. Full shutoff must be achieved if the system pressure falls to below the set pressure value, usually set at 90%.

How To Test Pressure Relief Valves

To ensure pressure relief valves maintain their effectiveness over time, a set pressure function test should be carried out at least once per year. At VMAC, we recommend inspecting pressure relieve valves annually for signs of corrosion or loss of functionality.

The pressure relief valve tests are the responsibility of the user or operator, while test instructions should be supplied by the air compressor manufacturer. For example, VMAC’s manuals include test instructions to perform a pressure relieve valve inspection:

“To test the pressure relief valve functionality, turn the system on and bring it up to operating pressure. Pull the ring on the pressure relief valve to depressurize the system. Turn the system off, and ensure the system comes back to operating pressure when the system is restarted. If the pressure relief valve is showing loss of functionality, contact your local, authorized VMAC dealer for a replacement part. Relief valve failure can result in air/oil tank over-pressurization leading to system failure or rupture.”

If you are operating a system that is not a VMAC air compressor, check your manual or contact the manufacturer for detailed instructions on how to test your pressure relief valve.

Related blogs:
Components of your VMAC mobile rotary screw air compressor system
The purpose and functions of compressed air storage tank
Why is my air compressor shutting off? Temperature sensors and switches

Why Is My Compressor Shutting Off? Temperature Sensors and Switches

Temperature Sensors and Switches

Temperature switches and sensors are used on applications which require a solution to a temperature control situation. Often less complicated than most electronic controls, temperature sensors and switches are relatively easy to set up.

Temperature sensors are often used for monitoring compressor coolant, oil and air inlet temperatures as well as discharge air temperatures and logging the variations.

Temperature switches are slightly more complex, and include a sensor plus the ability to send signals. A temperature switch senses temperature levels. When the temperature passes a set point the switch sends a signal to a controller to do something to the application, like cut the power, sound an alarm, turn on a light, or disengage the clutch.

Some immersion temperature switches are appropriate for applications that require an inexpensive solution to simple temperature control. These types of switches activate with a specific rise in temperature and are available with a wide range of temperature pre-set values as well as a set point range, set point tolerance, maximum temperature cut-out setting, and probe length.

On-off controllers

An on-off controller is the simplest form of temperature control device. The output from this type of device is either fully on or off, with no middle state. An on-off controller will cut power or disengage the clutch when the temperature passes the set-point. On-off control is usually used where a precise temperature control is not necessary.

A limit controller is an on-off controller used for alarm indication. This type of controller uses a latching relay, which must be manually reset, and is used to shut down a process when a certain temperature is reached.

VMAC temperature sensors, switches, and controls

VMAC air compressors are equipped with a switch which includes an oil temperature sensor. If the compressor oil gets too hot, the switch sends a signal to the on-off controller to disengage the air compressor’s clutch. This shuts down the system and prevents high temperature related damage.

Why is my compressor shutting off?

If your compressor trips on over temperature, it could be for any of the following reasons:

  • Ambient temperature too high or not enough ventilation
  • Too low oil level
  • Wrong type of oil being used
  • Dirty oil cooler
  • Thermostatic valve not working
  • Dirt / obstruction in oil lines
  • Plugged oil filter
  • Restricted air flow over the air to liquid cooler
  • Too high an engine liquid coolant supply temperature in a liquid to liquid cooler
  • Faulty temperature switch

Excessive oil temperatures can cause damage to your air compressor including premature lubricant degradation, high oil and moisture carryover, and varnishing of the compressor internals and system components (such as the oil filter, cooler, and separator filter). Lubricant flash points also present a fire hazard.

The costs related to rectifying these issues through the use of temperature switches and controls can result in significant cost-savings, as risks of down-time and injury are minimized.

Interested in learning more about air compressor components and accessories? Browse our collection of air compressor accessory blogs.


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Auxiliary port driven air compressor system considerations

Today many industrial engines come equipped, or can be ordered with, an auxiliary port (pump drive) that is used to power accessory equipment.  Quite often you will find a hydraulic pump or a standard piston type air compressor mounted there; what isn’t seen much is a rotary screw compressor mounted there.  We’ve had many inquiries asking if there is a compressor available that would meet the heavier duty cycle and air flow requirements for specific jobs.  These range from spray foam, pump priming, air gouging, to air tools and dust collection.  While VMAC does have direct drive, port mounted rotary screw compressors, there are several factors to consider before choosing to mount a rotary screw compressor to that auxiliary port. Continue reading “Auxiliary port driven air compressor system considerations”

The Purpose and Functions of Compressed Air Storage Tank

We’re often asked if a particular air compressor installation requires the use of an air receiver tank. Most applications will benefit from the use of air storage whether it’s a vertical or horizontal air tank. The choice of what style of tank is generally made by the installation location and the amount and type of space available. Vertical receiver tanks are readily available in sizes from 10 – 2560 Gallons, and horizontal receivers are available from 5 – 2560 Gallon capacities.
Continue reading “The Purpose and Functions of Compressed Air Storage Tank”

Components of your VMAC mobile rotary screw air compressor system

You’ve decided that a rotary screw compressor system is the right choice for your application; maybe you are converting from using reciprocating compressors. When installing your new compressor you’ll need to locate a few different components and plumb hosing between them. In this article, we’ll briefly explain the functions of the components of a rotary screw compressor system. Continue reading “Components of your VMAC mobile rotary screw air compressor system”

What are Dual Tower Regenerative Desiccant Air Dryers (and how do they work?)

Heaterless Type (Pressure Swing Dryers)

Dual tower desiccant air dryers are used to produce dewpoint temperatures below the freezing point of water, as well as reduce the moisture content of compressed air used in critical process applications. Typical dewpoints produced by these types of dryers are -40° F to -100° F, although lower dewpoints are possible. Continue reading “What are Dual Tower Regenerative Desiccant Air Dryers (and how do they work?)”

Why the fuel valve is important on small gas engines

Protect your engine, turn off your fuel

You just finished a job using your gas drive air compressor and you’re getting ready to drive to your next job. Did you remember to shut off your fuel valve?  In this article we’ll explain why you should.

Most small gas engines have a fuel valve that should be shut off by when the engine is not in use.  This can be easy to forget, especially when using remote controls.

Fuel shut-off becomes important when moving equipment as vibration can cause the carburetor needle valve to move allowing fuel to trickle into the carburetor, the float chamber and down the intake valve.  This can cause:

  1. Engine flood, causing downtime waiting for the flood to clear.
  2. Dilution, when fuel goes past piston rings and mixes with oil, causing engine damage.
  3. Hydraulic lock, when incompressible liquid causes engine damage or failure.
Best practice for small gas engines – ensure equipment is on level ground, and the fuel valve is shut off when re-fueling and when equipment is not in use.

Why does the engine flood?

Any time vibration causes the carburetor float to drop in the float chamber, pressure is reduced against the needle valve.  Reduced pressure against the needle valve allows pressurized fuel from the fuel tank to pass through the valve.

If this happens frequently, fuel will overfill the float chamber, flood down the throat of the carburetor, and flow into the cylinder through the open intake valve.

Fuel in the cylinder can flood the combustion chamber above the piston, creating hydraulic lock, preventing the engine from turning. This fuel will also slowly drain past the piston rings, diluting the oil in the crank case. If the engine manages to start with diluted oil, severe and premature engine damage will follow.

How does the float work?

The float chamber is located below the carburetor body. Through the operation of the float and the needle valve, the float chamber maintains a constant fuel level while the engine is working. The fuel flows from the tank into the float chamber through the needle valve. When the fuel rises to a specific level, the float rises. When the buoyancy of the float is balanced with the fuel pressure, the needle valve shuts off the fuel passage, thereby maintaining the fuel at the predetermined level.

Any other reasons?

Not only does shutting off the fuel valve prevent the engine from flooding while being transported, it prevents flooding because of contamination in the float valve, and extends the life of the float valve by decreasing pressure on it.

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Is this unique to Honda engines?

Most manufacturers of small gas engines have this same issue.  Like the Honda engines used in VMAC G30 Gas Drive Air Compressors, Subaru and Kohler engines used in other air compressor brands state in their literature that fuel valves should be shut off when not in use, including during transport.

VMAC G30 Gas Drive Air Compressors are powered by Honda’s GX390 air cooled 4-stroke engine.  The G30 is a Honda-approved application.  The engine includes electric start capability, is EPA and CARB-compliant, and comes with Honda’s 3-year warranty.

Do you have questions about VMAC’s G30 Gas Drive Air Compressor?  Please give us a call at 1 888 514 6656 or email us at [email protected].

If you have any questions about this article or anything mobile compressor related, please contact us.

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.


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.


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.

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Factors to consider when purchasing a compressor for your mobile application

It’s time to buy a compressor for your mobile service truck application.  You’ve figured out what type of compressor and how much air flow and pressure you need as well as how it will affect the load capacity of your truck.  Now it’s simply where you can buy that compressor the at the lowest cost, right?  Well not really.  Besides the installation time, there are some important installation details to consider, depending on the type of compressor you’ve chosen and what type of work you’ll be doing. Continue reading “Factors to consider when purchasing a compressor for your mobile application”

Checking VMAC Belt Drive Systems

Checking for belt misalignment and belt drive design requirements.

VMAC compressor systems use serpentine belts, also known as a micro-v, poly-v or multi-rib belts, which are continuous rubber belts with k-type cross section typically with 6 ribs but can vary between 4 and 8 ribs. Belt drive systems are designed to take into account many different requirements to allow continuous smooth running with minimal maintenance. Some of these requirements are: Continue reading “Checking VMAC Belt Drive Systems”

5 Ways To Reuse Your Air Tank (Now That You Don’t Need One)

One of the coolest benefits of rotary screw air compressors is that they don’t need an air receiver tank. Instead, these powerhouse air compressors operate at 100% duty cycle and provide instant air on demand.

But there’s one “problem” that many operators experience after they upgrade their recip to rotary screw: their old air receiver tank is suddenly a stationary, unnecessary hunk of metal.

Fortunately, we’re here to help. In this post, we’ve put together a list of five ways to reuse an air tank now that you don’t need one…
Continue reading “5 Ways To Reuse Your Air Tank (Now That You Don’t Need One)”