the mechanical separator just prior to the purification system. If your compressor is running too hot, which can occur if the compressor is located in a small room with little or no ventilation, it will shorten the life of your filter cartridge. It is important to provide fresh, uncontaminated air to the compressor’s intake. Gross contamination of the intake air will affect the efficiency of the purification filters which could subsequently affect the air quality produced by the compressor. When dealing with a 500 ppm limit for CO2, assuring that the intake air quality is acceptable is especially important. As a point of interest, from 1911 to 2004, the CO2 concentration in ambient air has increased from 300 to 377 ppmv or about 25%, most of it released since 1966.
CO2 is a by-product of motor exhaust, human respiration, and natural decay of organic material. Purification filters containing catalysts can also cause a slight elevation in CO2 because they are designed to convert CO to CO2. This is actually beneficial since carbon monoxide (CO) even at low levels is much more harmful than CO2. Any time a number of people are inside closed quarters, levels can easily reach 600 ppm or more. HVAC systems in offices or retail stores usually do not bring enough fresh air from the outside to significantly reduce the level of CO2 that can build up. When facing CO2 levels that are slightly over the limit, opening windows/doors, using fans, and raising the intake location to ceiling height may help. This must be done each time the compressor is used to charge a cylinder because passing an air test is important but not as important as routinely providing safe air for filling scuba or scbas. However, if levels are consistently high, the most common solution is moving the intake location outside.
Prior to moving the intake, take a survey of the neighborhood at different times of the day, for several days. Keep in mind that outside air can be contaminated by exhausts from such common sources as dry cleaners, beauty salons, paint/body shops, heavy industry, and of course vehicle/motor exhaust. These conditions can cause the outside air to be an inappropriate source for your compressor intake. If unsure, air samples can be taken and submitted for laboratory analysis. If you have an outside intake, you should always be alert to outside conditions that might affect your air quality throughout the year. During these times, the compressor should not be operated.
Generally speaking, the intake pipe can be sized in accordance with the following guidelines:
If more than 4 elbows are used, every 2, 90° elbows should be treated as 10 feet of pipe,
It is best to keep the piping as short and straight as possible. Minimum height should be 8-10 feet, but we’ve found that above roof line almost always works. Do not place downwind of heating or air conditioning vents. 90° elbows and the total distance of intake piping should be kept to a minimum to prevent any restriction of the air flow.
The end of the intake piping should point downward to avoid excess water from entering the compressor intake. It should be covered with a fine mesh screen to eliminate blockage by dirt, leaves, bird nests, and other debris. Caution should be taken to assure the surface area is large enough so that it will not restrict the air intake.
Intake piping should be made of a type of material like PVC that will not contribute to contamination by corrosion or chemical interaction. If using glue, allow sufficient time for glue vapors to dissipate before using. (If PVC cement used, allow 4 weeks to off-gas, if silicone rubber sealant used, use only on outside of piping and allow 2 days to off-gas.) Connection of piping to the compressor can be accomplished with a short piece of flexible tubing. Do not use rubber or collapsible tubing. Corrugated vacuum cleaner hose or pool vacuum hose works well. The compressor’s intake filter should not be removed but left in service.
What needs to be understood about the purification process of high pressure compressed breathing air is that the technology available today cannot produce inexpensive filters to efficiently and consistently remove carbon dioxide for the entire life of the cartridge. During the first few hours of operation levels of CO2 can be reduced in a new filter cartridge that contains molecular sieve. This is due to the absorption of CO2 by the molecular sieve. The filter will then perform as designed which means that moisture will be preferentially removed from the air stream. Since the molecular sieve prefers water over CO2, when water is sufficiently absorbed the CO2 molecules will be released. This can cause a gradual increase in CO2 or if a large amount of water is absorbed quickly, the release of accumulated CO2 could be significant.
All filter cartridges have a limited service life. Filter life is determined by the moisture content of the air being delivered to the filter cartridge. Water content is a function of how effective the compressor separators remove liquid water entrained in the air stream and the air temperature. Assuming the separators are 100% efficient, the amount of water in vapor form that reaches the desiccant (molecular sieve) per unit mass of gas compressed is a function of temperature, e.g. the higher the temperature the more water vapor. Most high pressure breathing air compressors on the market now can function in an environment as high as 100°F. If an environmental temperature this high can be avoided by good room ventilation, etc. it will ultimately translate into cooler air temperatures entering the filter system and longer filter life. Filter life (in terms of processed air volume) can be directly correlated with the amount of water vapor that must be removed from a saturated air stream.
For example: If a compressor is located in a closet-like room, without access to outside, fresh air; temperatures (even if air conditioned) can rise to 100°F at the separator inlet. This can drastically reduce the actual number of hours the filter can be used. It is feasible that a filter rated for 40 hours, could only safely be used for 20 hours under the above noted conditions. For further information, write down your compressor’s make, model, scfm, and psi, filter brand and stock number, and typical ambient temperatures or if possible separator inlet temperatures. Then, contact your compressor manufacturer to discuss your specific situation.
As mentioned earlier, filters are designed to remove carbon monoxide by converting it to CO2. The filter will then hold the CO2 along with other removed impurities. If a sudden pressure drop should occur, like when the bleed valve to the purification chamber is opened too quickly or a sudden failure of the pressure maintaining valve occurs, then CO2 and other contaminants can be released into the air stream. Another scenario that can cause high CO2 levels is when a purification filter is not removed but moved up the chain of cartridges to a front position or when it has reached its maximum efficiency. Some filters have a moisture indicator strip on the outside of the cartridge. Even though the strip may not indicate that it is time to be removed, it should not be assumed that the filter is “good as new.” A filter is like a sponge, it can hold on to unknown quantities of CO2 or gaseous hydrocarbons. When it becomes completely saturated, like a sponge, it will not continue to remove but allow contaminants to simply pass through. If a pressure drop occurs at this point, large amounts of CO2 and/or gaseous hydrocarbons can be released.
To provide the best conditions for a safe air supply that complies with CGA Grade E specifications, follow these guidelines:
If you have further questions, or need assistance in resolving this problem, please Contact Us or give us a call at 1-800-247-1024. You are entitled to a free resample. Please use the supplies you have on hand to take a retest. Once we have received your sample (you have 30 days) we will restock your kit.
The AirCheck AirCheck✓™ Team of Experts would like to thank you for your continued business!