Frequently Asked Questions

What is Pressure Swing Adsorption (PSA) Technology?

PSA is one of several technologies currently in use for separating oxygen from air.

How does PSA work?

PSA incorporates a material called molecular sieve for gas separation. This zeolite based sieve has a preferential adsorption for nitrogen. Clean dry air is passed through the sieve beds on the oxygen generator, producing an oxygen enriched gas.

Does an oxygen generator have to be indoors?

Standard OGSI oxygen generators are designed for use indoors.

Does the equipment have to be air conditioned?

PSA oxygen generators provide the best performance in temperatures between 40 degrees F (4 degrees C) and 80 degrees F (27 degrees C).

Does the equipment room require humidity control?

PSA oxygen generators provide the best performance when the feed air has a dew point of 40 degrees F & (4 degrees C) or less. Depending on the model selected and or the feed air equipment (air compressor, dryer, air surge tank and feed air filters) supplied, humidity control may or may not be required for the room. Consult factory for recommendations on a specific applications.

Can the air preparation equipment be located in a separate area from the oxygen generator?

The air preparation or feed air equipment can be located in adifferent room than the oxygen generator.

What are the maintenance requirements of PSA oxygen generators?

PSA oxygen generators have internal filters that have recommended element replacement about every 6 months under 24/7 operation. Additionally, valves will have to be rebuilt every few years. The majority of the maintenance will involve the service of the air compressor recommended by the air compressor manufacturer.

How long does the molecular sieve last?

The molecular sieve life is based on the feed air quality. If the feed air quality always meets recommended standards, the sieve can last indefinitely (20 years or more!) If the molecular sieve ever became contaminated by oil, dirt or water can it be cleaned or replaced? If the molecular sieve is contaminated by oil it will have to be replaced. Water contamination, based on degree, does not necessarily mean that the sieve will need to be replaced. Dirt is a rare cause of sieve replacement, but other contaminates like ammonia can cause sieve failure. Consult factory for specific air contamination that may be present at the generator site.

Can the oxygen generator be operated with contaminated sieve, and what are the consequences?

A PSA oxygen generator may still operate after it has been contaminated, but a reduction in oxygen purity and flow should be expected. This may be critical in many applications, such as hospitals where the oxygen is being inhaled.

Is it easy to replace the molecular sieve and how much does it cost?

All OGSI oxygen generators are designed so that the sieve can be changed in the field. The cost of the sieve change depends on the generator model and size.

Is molecular sieve readily available, or is or is hard to get in many localities?

There are several suppliers of sieve worldwide.

Is all zeolite molecular sieve the same?

>Not all zeolite based sieves are the same, and can vary even by brands made in different locations (USA vs. foreign made).

Can I use a regular compressor, or do I need an oil-free compressor?

An oil- free compressor is not required for PSA oxygen generation as long as the feed air quality is maintained.

Can any air compressor be used with OGSI PSA O2 generators?

We would recommend only good quality feed air equipment (air compressor, dryer & feed air filter set) that can meet our air quality requirement of ISO 8573.1 class 1.4.1.  The details of this specification are shown on our general arrangement drawing for each model.  We also recommend using a good quality feed air equipment so the feed air is as good into the future as it was on day one.

Do oil-free compressors cost more than regular compressors?

Oil-free air compressors generally cost significantly more than oil lubricated versions.

What happens if the air compressor malfunctions and oil is introduced into the air line?

Excessive oil discharge from an air compressor can damage a PSA oxygen generator by contaminating the molecular sieve.

Do I need a dryer for the air preparation?

The feed air quality specification for OGSI PSA oxygen generators requires a dew point value of 40 degrees F(4 degrees C) or less. If the local ambient air conditions are above this value, an air dryer will be required.

Do you need a dessicant dryer for the air prep or can I use a standard refrigeration dryer?

A desiccant dryer is not required for air preparation, in most cases a refrigerated dryer is sufficient.

Can I use a dessicant dryer if I want, and are there any advantages or disadvantages?

A desiccant dryer can be used in place of a refrigerated dryer, and slightly better performance from the oxygen generator can be expected. However, this increase in performance may not offset energy and cost penalties.

What happens if the air dryer malfunctions or stops working?

If a required air dryer fails, damage to the PSA oxygen generator can occur due to moisture contamination of the sieve.

Do you size systems differently for different altitudes?

The size of the air compressor for a PSA oxygen generator has to be factored for site elevation. Higher elevations will require a larger air compressor.

What is the purity of oxygen produced by PSA?

The oxygen purity from OGSI generators can range from 93 to 95%, with 99% being optionally available (certain criteria must be present).

What is the dew point of the oxygen produced by PSA?

The dew point of the produced oxygen from a PSA oxygen generator will be -60 degrees F (-51 degrees C) to -100 degrees F (-73 degrees C) depending on the generator size.

What is the standard pressure of oxygen pressure produced by PSA?

The output pressure from most OGSI oxygen (Model OG-25 and up) generators is 45 psig (3 bar gage) to 60 psig(4 bar gage), with higher pressures optionally available by means of an oxygen booster.

Do different models of oxygen generators produce oxygen at different pressure levels?

The Models OG-15 and OG-20 produce oxygen at pressure of 9 psig (.62 bar gage) and 15 psig (1.03 bar gage) respectively.

Can you increase the pressure to a higher level?

The delivery pressure of oxygen from a PSA oxygen generator can usually be increased to the high end of the scale by decreasing the flow from the plant. Higher pressures would require an oxygen booster or compressor.

Can you provide 7 or 8 Bar pressure?

With an oxygen booster, pressures of 8 bar and above are possible.

Liquid oxygen has purity of 99% . . . is that better than 93% oxygen?

Liquid oxygen (LOX) at 99% oxygen purity may have some advantages for metal cutting, but not necessarily for medical applications.

If the standard purity of PSA oxygen is 93% +-3%, can I stake steps to produce oxygen at the higher end of range, for instance 95%?

If a PSA oxygen generator is run at 80% or less of its rated output, continuous oxygen purity up to 95.3% is possible.

Are there different pharmacopoeia standards for 99% and 93% oxygen?

The US Pharmacopoeia Standard, which is used by the US FDA and many other medical authorities, has oxygen specifications of 93% and 99%.

Why do some countries specify 99%?

Some local authorities require 99% purity oxygen due to old regulations and ordinances. However, with the acceptance of international specifications from CSA (Canada) and ISO 10083 (European) these older specifications are being revised to 93%.

What is the difference between an oxygen concentrator and an oxygen generator?

These terms have been used interchangeably, with oxygen concentrator being the most technically accurate. Generically, oxygen concentrators describe smaller home medical systems, and oxygen generators describe all other size plants.

If millions of people, world-wide, use oxygen concentrators that produce 93% oxygen on a daily basis, why do some countries still specify 99% oxygen hospital supply systems?

There have been powerful competitive interests that have lobbied local authorities to maintain a 99% medical oxygen purity standard to prevent the introduction of less expensive alternatives like PSA oxygen generators.

Liquid oxygen has losses where a certain amount is lost to evaporation. Does PSA gaseous oxygen have the same problem?

It is normal for a LOX storage tank to bleed off 1 to 4% of the tank volume to prevent pressure built-up. This is not a factor with PSA oxygen generators, all the oxygen that is produced can be used, there is no bleed off.

Are there recommendations for a typical hospital oxygen supply system?

There are CSA and ISO specifications that contain information on hospital oxygen systems.

Can I monitor my oxygen generator system from a remote location?

OGSI provides a Telemetric Communication Option for remote monitoring of the oxygen generator on Models OG-250 and larger.

How do I size a hospital PSA oxygen system?

Ideally, the hospital would design specifications or historical data to determine the plant size required. If this information is not available a formula can be used to estimate the peak oxygen required. Refer to the OGSI Hospital Application Note for details.

What are some of the benefits of a PSA oxygen system compared to using cylinders or liquid oxygen?

With a PSA oxygen system you eliminate all the cost and problems of delivered oxygen (higher prices, delivery costs, supply problems to name a few)

Are there concerns about carbon monoxide and carbob dioxide when producing gaseous oxygen
using PSA technology?

Most specifications for medical or breathable oxygen have maximum levels of carbon monoxide and carbon dioxide. It is important that the oxygen system has access to clean fresh air, and that a carbon monoxide and carbon dioxide monitor be used for medical or breathable applications.

Is there equipmant available that wold allow OGSI to diagnose an oxygen generator problem from the factory in New York without having to travel to the job site?

OGSI provides a Telemetric Communication Option for remote monitoring of the oxygen generator on Models OG-250 and larger.

Can the system be set to automatically turn off if there are problems?

Depending on what sensors are used (dew point, oxygen purity carbon monoxide and carbon dioxide levels, flow etc.) the plant can be configured to shut down based on any number of parameters.

Can an oxygen cylinder get contaminated?

It is possible that an oxygen (or any other type of gas cylinder) can become contaminated due to misuse.  For this reason OGSI offers vacuum pumps on most CFP Models so that cylinders can be evacuated before they are filled.


How long does an oxygen cylinder last and does it have to be re-certified on a periodic basis?

The oxygen in a cylinder can last indefinitely. In the US, the DOT requires that aluminum cylinders be hydro-tested every (5) years, and steel cylinders every (10) years.

Do I need to use a vacuum pump to empty a cylinder before re-filling?

It is never a bad idea to use a vacuum pump to empty a cylinder before it is refilled, especially if the cylinder is out of the control of the filler. This vacuum procedure can be eliminated if the cylinder is always in control of the filler.

Why are carbon filters used to produce medical grade oxygen?

Carbon filters can provide an extra measure of filtration on medical or breathable oxygen systems, and additionally eliminate system odors.

What is the most cost-effective oxygen cylinder filling plant?

The OGSI Model CFP-500 and CFP-1000 provide two of our best values, due to optimal sizing of the oxygen compressor.

Why do several models of cylinder plants cost almost the same, but produce very different amounts of oxygen?

On smaller CFPs, the price does not change proportionately with plant size because of the standard equipment and instrumentation included with each skid. Also, there are only three standard sizes of oxygen compressors.

Can I reduce the cost of my system and just use an oxygen monitor?

If the application is not for medical or breathable use, costs can be reduced by eliminating the carbon monoxide and carbon dioxide monitor.

How do carbon monoxide, carbon dioxide, and oxygen monitors work? Do they wear out?

There are various different types of sensor technologies available for gas monitoring. OGSI uses chemical depleting sensors, which have to be replaced over time.

If I sell or rent oxygen cylinders, how many cylinders do I need?

It is generally accepted that a 10 to 1 ratio of cylinders is required based on the output of the plant. For example, if a CFP-500 produces (50) cylinders per day, then (500) cylinders may be required to service the market. This ratio may change if the customer supplies the cylinder.

Are there different valves used on cylinders?

For steel oxygen cylinders there are (2) major types of valvesused worldwide, the US based type CGA 540, and the British based type BS # 3. DIN type versions are also being used.

What equipment do I need to transfill a small cylinder from a large cylinder?

A high pressure flexible hose with an on/off valve and the corresponding cylinder valve connections at each end would be required. For safety, a containment vessel or chamber for the cylinder being filled is also recommended.

How much does it cost to fill a cylinder of oxygen using PSA oxygen?

For PSA oxygen generators, the cost for oxygen production, or cylinder filling is normally stated in kilowatt hours (KWH). The reason being that the air is free, but there is a cost of electricity to operate the air compressor. At a sea level site elevation, it will cost about 10 KWH to fill a 6m3 size oxygen cylinder, or 1.5 KWH per M3.

How much energy does it take to run just a PSA oxygen generator?

The amount of power required to operate just the PSA oxygen generator is negligible, about 50 watts, for control circuits.

How big is a PSA oxygen generator system?

Most OGSI oxygen systems will fit into a 20 or 40-foot ocean shipping container.

Can I mount a PSA oxygen generator system on a skid?

Yes, you can mount a PSA oxygen generator on a skid, but it must be in the vertical position to operate properly.

Does OGSI test every oxygen generator before shipping to the job site?

Every OGSI oxygen system is tested at the factory.

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