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Van Air Systems

Phone: 1-800-840-9906

2950 Mechanic Street
Lake City, PA 16423 USA



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As in any highly focused industry, the terminology surrounding compressed air and gas treatment can be confusing to the non-specialist. To better serve Van Air customers, Van Air distributors, and those wishing to better understand compressed air and gas treatment, a glossary of common industry terms is below.


Have a question, we have an answer.

The trade name for Van Air Systems' most aggressive deliquescent desiccant, which establishes a 10% - 13% relative humidity in air or gas lines. The most common application for 10BF is the dehydration of natural gas for meeting pipeline water content specifications.

Pressure measured from absolute 0 as a base. It is the sum of atmospheric and gauge pressure. 100 PSIG + 1 atmosphere (14.7 PSIA at sea level) = 114.7 Pounds per Square Inch Absolute (PSIA).

The action of a material which is itself changed chemically in extracting one or more substances present in an atmosphere of gases.

Actual cubic feet per minute, usually defined as a pressure other than sea level. It is a measure of flow rate.

Substance that have the ability to attract and hold a gas, liquid or dissolved substance on its surface, but does not physically or chemically change. Activated alumina, silica gel, and molecular sieve are examples.

A device used down stream of a dryer in a compressed air drying system, often used for preventing the downstream migration of fine desiccant particles.
A device used in a compressed air system to hold a specific volume of air .
American National Standards Institute (Common term used in piping standards e.g. ANSI B31.1 Piping)
American Society of Mecanical Engineers. This body defines the widely accepted code and standards under which pressure vessels are manufactured.
A valve used to automatically drain condensed liquids, normally activated by timers, or liquid level detection.
Filtration media used in the design of Van Air filter elements to stop small particles from migrating.
The rapid vibratory movement of extremely small particles suspended in a fluid, caused by bombardment of the particle by the moving molecules of the fluid.
British Thermal Unit -- The amount of energy required to raise one pound of water by one degree Fahrenheit.
Clean Dry Air.
Air/Gas flow term, Cubic feet per minute, see also ACFM and SCFM.
The primary federal law in the U.S. governing water pollution with the goal of eliminating releases of high amounts of toxic substances to water. In many compressed air systems oil laden condensate must be treated with an oil/water separator prior to disposal in order to maintain compliance with the Clean Water Act.
The flow direction of the gas being dried and the regeneration (purge) gas flow is the same.
To change from a gas to a liquid by removing heat or elevating it partial pressure.
Purge flow gas direction is the opposite of that of the gas being dried.
Extends the cycle of a heated dryer that has the dew point demand option under low moisture load conditions.
The time required for a desiccant bed to go through one drying period and one regeneration period.
A compound or mixture that is so hygroscopic that it eventually dissolves in the water it absorbs.
A compressed air or gas dryer that uses deliquescent desiccants to remove entrained water vapor.
A material used for drying purposes.
The difference between the inlet dew point to the dryer and the outlet dew point exiting the dryer. Typically used in single tower deliquescent dryers where the depression is a function of the absorbent drying medium.
Natural gas produced by the digestion or fermentation of organic matter, also known as Biogas.
The desiccant capacity of a dynamic (changing) system.
The desiccant capacity at constant, static conditions.
Heated Regenerative air dryer that uses an external heater and expanded compressed air purge to regenerate its desiccant beds. (See also heated purge)
Automatic drain that uses a float to activate the draining device.
Unit of weight measurement. One pound = 7000 grains.
Regenerative air dryer that uses the principle of pressure swing adsorption and purge air to regenerate the desiccant bed, without the introduction of heat from a heater. Also known as Pressure swing and Heaterless dryer.
The aging of adsorbent desiccant due to moisture and/or heating of the desiccant for regeneration.
Inertial energy on an aerosol causes it to break away from the gas streamline, hit a filter fiber and stick to it.
ISA-S7.3 states that instrument quality air is air that is a pressure dew point that is 18F/10C below the minimum temperature that the air system will see.
Valve logic that ensures that the off stream tower has repressurized and that the signal has been given to the inlet transfer valve to move position and that the transfer valve has moved. If any of the functions required for valve transfer to change positions has not occurred the inlet transfer valve does not switch towers.
The condition of constant temperature.
The amount of energy in the form of heat released or absorbed by a substance during a change of phase, i.e. between a solid, liquid, or gas. No temperature change is involved.
Compressor that uses lubrication to run, typically compressor oil that can contaminate down stream equipment if it is not removed.
Maximum Allowable Working Pressure - The highest pressure allowed for safe operation.
1000 Cubic Feet per Day - a measure of flow of air/gas.
Measurement of particle size equal to 1 millionth (0.000001) of a meter.
1,000,000 Cubic Feet - a measure of volume of air/gas M = 1000
Device used to remove liquid from compressed air/gas.
Adsorbent desiccant typically used in regenerative air dryers or point of use dryers to obtain -40F or as low as -100F Pressure dew point.
A white solid formed by the combination of methane and water at various temperature and pressure conditions.
The refrigeration compressor runs continuously based on the inlet conditions. It normally requires a hot gas bypass valve for proper temperature control.
Oil that has been heated high enough to change into a vapor, coalescing filters generally can not remove this type of oil.
Filter that uses the principles of outside to inside flow to allow solid contaminants to be removed from incoming air/gas on the outside of the filter element.
Metal pieces normally formed from rust due to moisture and corrosion of metal piping.
Filters used ahead of regenerative desiccant dryers or refrigerated dryers to protect desiccant beds and heat exchangers from oil and particulate contamination.
Moisture content of air/gas at the pressure where it is being used. For most applications this is at or near 100 PSIG, whereas atmospheric dew point is the moisture after it has been expanded to atmosphere.
A technology used to separate constituent gases under pressure according to a particular species affinity for an adsorbent material. In a PSA compressed air dryer, regeneration of the adsorbent desiccant is accomplished with dry purge air only.
Pounds per Square Inch Differential - A unit of measure used for stating pressure drop in a system.
The air that is expanded to atmospheric pressure and used to regenerate off stream towers in regenerative dryers.
Compressed Air or atmospheric air used to remove moisture from a desiccant bed during the regeneration period.
A substance which produces a cooling effect by absorbing heat while vaporizing. Examples: Ammonia, halocarbons, water, etc.
The period of driving moisture from an adsorbent desiccant so that the material can be reused.
The actual quantity of water vapor in an air or gas sample compared to the quanity that would exisit if the sample were saturated. It is normally expressed as a percentage.
A system that can no longer hold any more of a particular substance. Air at 100% humidity is said to be saturated.
Heat transfer which results in a change of temperature.
Siloxane is any chemical compound composed of units of the form R2SiO, where R is a hydrogen atom or a hydrocarbon group. Siloxanes are common contaminants in landfill gas and digester gas generated in waste water treatment plants. Drying these gases has been shown to substantially reduce the concentration of siloxanes.
Deviceused in a refrigerant suction line to evaporate liquid refrigerant so that it does not enter the refrigeration compressor.
A dryer that reactivates by the heating of its desiccant bed.
Regenerative dryer which can be either heatless or heated design, using one tower to dry while the other tower is regenerated, then switching towers on a NEMA time cycle.
Compressed air is often called the 4th utility because it is as necessary to plant operation as water, gas or electricity.
A material which is changed physically and/or chemically in extracting one or more substances that are present in a mixture of gases or liquids. Dry-o-Lite, SP, and 10BF are examples of Van Air absorbent desiccants
Used in a refrigeration system to store refrigerant and protect the refrigeration compressor from being damaged by liquid.
Adsorbent desiccant typically used in regenerative air dryers or point of use dryers to obtain -40F Pressure dew point.
The collection of a vapor in condesed form on surface of an adsorbent. Common adsorbents include silica gel, activated carbon, activated alumina, and molecular sieves.
A device used to cool air temperature and removed moisture from compressed air. They can be water cooled or air cooled.
Surrounding on all sides. Usually refers to atmospheric air surrounding pipes and equipment in a compressed air or gas system.
The difference between the inlet temperature of a cooling medium (ambient air, water, water-glycol, etc.) and the temperature of the air at the outlet of the aftercooler or heat exchanger.
Unit of pressure equal to 14.7 PSI at sea level.
Heated Regenerative air dryer that uses an external blower for purge air to avoid compressed air loss.
When the leading edge of the mass transfer zone in a regenerative desiccant dryer reaches the discharge side of the desiccant bed.
Benzene, Toluene, Ethylbenzene, & Xylene which are volatile compounds found in petroleum derivatives and natural gas. The emission of these compounds is frequently a drawback associated with glycol-type natural gas dehydration systems.
Compressed Air & Gas Institute which is an organization of compressor and dryer manufacturers.
Blower unit that uses multiple fan blades rotating around a shft to draw air in along the shaft. Typically used in blower purge air dryers in place of purge make up air.
One of a number of pieces of legislation regarding the reduction of smog and air pollution in general. In natural gas applications, Triethylene Glycol (TEG) dehydrators can produce BETX and VOC emissions in violation of the Clean Air Act. Van Air deliquescent desiccant systems can be used to dry natural gas while producing no emissions. See:,1,Natural Gas Dehydration
Filter that uses the principles of inside to outside flow to allow vaporous contaminants to condense and be removed from incoming air/gas.
The ratio of absolute pressure / atmospheric pressure, where atmospheric pressure is typically 14.7 PSIA and Absolute pressure is gauge pressure + atmospheric pressure 14.7 PSIA. Eg. At 90 PSIG the compression ratio is (90 + 14.7 PSIA)/14.7 PSIA or 7.12 to 1.
The time for a molecule in a gas stream to flow through a desiccant bed.
Flow rate efficiency = G.P.M. flow rate of 60�F water with 1 PSID max.
Energy Saving Feature that is offered as an option on heatless dryer models HL-200 through HL-2500 (Comes Standard on HL dryers 3000 SCFM and above) Includes power on/off switch, power on LED, Cycle mode pushbutton, Fixed and auto mode LEDs, Energy Savings LED, Switching failure LED, Reset Pushbutton, L/R tower drying and tower regenerating LED's
The refrigeration compressor turns off and on based on the moisture load to the dryer, enabling the dryer to be energy efficient.
A chemical or mixture of chemicals that absorb moisture from the surrounding air or gas, disolving (deliquescing) in the process.
Filter medium that catches particles and aerosols throughout the element, vs. only on it surface.
The temperature at which water vapor begins to condense. It is also the point where relative humidity is 100%, or wet bulb = dry bulb.
The movement of particles from a high concentration to a lower concentration.
Van Air trade name of Absorbent desiccant material that produces a 55% critical relative humidity.
Energy Saving Feature that is offered as an option on Van Air heatless dryer models HL-200 through HL-2500 (Optional on HL dryers 3000 SCFM and above) Includes power on/off pushbutton/light, Cycle selector switch fixed/auto, Energy Savings light, Switching Failure light & reset, High Humidity light & reset, L/R tower drying and tower regenerating lights.
Heat exchanger where refrigerant is evaporated to produce cooling.
Alarm used on regenerative air dryers that indicates when the dryer fails to switch towers or is seeing an elevated pressure on an off stream tower.
A device that prevents a fluid level from rising beyond a predetermined point.
Heated Regenerative air dryer that uses an external heater and expanded compressed air purge to regenerate its desiccant beds. (See also exhaust purge)
Refrigerated dryer device that injects hot gas into the evaporator to elevate temperature and prevent freezing.
A material which attracts moisture.
The valve on a regenerative dryer that shifts flow from one tower to another.
A particle or aerosol is removed because it is larger than the opening in the filter media.
Heated Regenerative air dryer that uses an internal heater in an isolation tube and expanded compressed air to regenerate its desiccant bed.
Natural Gas produced by the decomposition of materials in a landfill.
Natural gas that does not meet the normal pipeline standard of 1000 BTUs per cubic foot.
The length of desiccant bed required for the moisture concentration gradient of the desiccant bed to go from inlet gas conditions to maxium dryness.
1000 Cubic feet - measure of volume of air/gas.
Natural gas that does not meet the normal pipeline standard of 1000 BTUs per cubic foot.
Filtration device used to remove large amounts of oil vapor from air/gas stream through Brownian motion/diffusion.
1,000,000 Cubic Feet per Day - a measure of flow of air/gas M = 1000 (M*M = 1 million)
The amount of moisture that is specified or allowed for air/gas.
Material Safety Data Sheet - Data sheet that shows safety information for different materials.
National Electric Manufacturers Association - Standards that are set for different NEMA ratings of equipment and control boxes eg. NEMA 12, 4, 4X, 7. They have also defined cycle as the time for a function to complete its operation and return to its original point, e.g. a 10 min NEMA cycle is a cycle where the air dryer is used for 5 minutes and then regenerated for 5 minutes taking 10 minutes for a full cycle.
Compressor that does not use lubrication, also known as an oil free compressor.
Term for the downstream valve on regenerative dryers. Generally used in larger systems or older style regenerative air dryers.
Gas that has a value of 1000 BTU per standard cubic foot and a dryness of 5-10 pounds of water per million standard cubic feet.
A device that is directly ahead of where its output is used. Examples are point of use dryers and filters. They normally are smaller in flow rating and size than the entire system.
Heat exchanger in a refrigerated dryer system. It precools air to the refrigerant/air heat exchanger and reheats air leaving the refrigerant/air heat exchanger.
Loss of pressure due to changes in size or accumulation of contaminants. Compressed air equipment has an inherent pressure drop that changes with contamination and piping has a pressure drop due to friction because of pipe sizes, expansion, contraction and directional changes.
Pounds per Square Inch.
Gauge pressure (Pounds per square inch gauge).
Muffler that is used to lower to sound from the exhaust of a regenerative dryer.
The amount of purge air that is used for a regenerative air dryer. On heatless , exhaust purge and internally heated compressed air dryers this air is deducted from incoming air to regenerate the adsorbent desiccant bed.
Compressed air dryer that removes moisture by lowering air temperature. It is normally reheated to also reduce humidity.
Twin tower dryer which can be either heatless or heated design, using one tower to dry while the other tower is regenerated, then switching towers on a NEMA time cycle.
Pressure relieving valve used on vessels to ensure that pressure does not build up and cause damage. Typically used as a safety device on equipment downstream of a compressor.
Standard Cubic Feet per Minute. One cubic foot of a gas at 14.7 psi, 68�F, and 36% relative humidity.
Clear pressure window that allows someone to see inside a device.
Van Air trade name of an absorbent deliquescent desiccant material that produces a 33% critical relative humidity.
Flow velocity of a gas molecule through the cross-sectional area of the empty desiccant vessel.
100 F inlet temperature, 100 PSIG, 100 F ambient - The operating standards used by most manufacturers to rate compressed air/gas dryers.
Drain valve where there is no inherent loss of air to operate