How to Size an Air Compressor for a Laboratory Nitrogen Generator

To size an air compressor for a laboratory nitrogen generator, find the generator's feed-air consumption at your target nitrogen purity and flow, account for pressure losses and simultaneous loads, then confirm the compressor can deliver that flow above the generator's minimum inlet pressure — continuously, not just at its rated maximum. Generator nitrogen output is never the right sizing basis.

Below is the six-step workflow we recommend, followed by a worked example and the answer to a common sizing mistake.

The six-step sizing workflow

Step 1: Find the generator's required feed-air flow at your target purity and output

Generator manufacturers publish feed-air consumption tables that vary with inlet pressure and nitrogen purity. These are not optional specs — they are the actual compressed-air demand your compressor must satisfy.

For Organomation's NITRO-GEN, the published compressor-specification document lists feed-air consumption at minimum nitrogen flow. Two supported operating points: at 58 psi inlet and 99% purity, the generator consumes 19.33 L/min of compressed air to produce 2.5 L/min of nitrogen; at 73 psi inlet and 97% purity, it consumes 29.67 L/min to produce 8 L/min of nitrogen. Other generator manufacturers publish equivalent specifications — obtain the feed-air consumption data for the specific model you are pairing.

Step 2: Identify the generator's minimum inlet pressure

This is the pressure the generator must receive at its connection, not the pressure at the compressor outlet. Tubing, hoses, fittings, and any coalescing or drying stages between the compressor and generator introduce pressure drop.

Peak's Infinity XE membrane generators require a minimum inlet pressure of 60 psi. The NITRO-GEN's feed-air tables list operating points beginning at 58 psi inlet.

Step 3: Compare the generator's demand with compressor output at that pressure

Compare the generator's feed-air demand with the compressor's delivered capacity at the required operating pressure, using matching flow-reference conditions. Do not rely on displacement or an unspecified headline capacity.

Delivered capacity at an operating pressure may itself be expressed as free-air delivery. Per the Atlas Copco Compressed Air Manual, FAD is defined as the compressor's output flow rate recalculated to a free-air volume rate at the standard inlet condition — inlet pressure 1 bar(a) and inlet temperature 20 °C — and is stated separately from Normal liters/second (Nl/s), which is recalculated to 1.013 bar(a) and 0 °C. Consult the compressor manufacturer's documentation for the reference conditions used in its capacity ratings before comparing figures.

Obtain the compressor's delivered-capacity data at your required operating pressure from the manufacturer before completing this step.

Step 4: Account for pressure losses, dryer consumption, and simultaneous loads

Separate two different allowances:

- Flow demand: the generator's feed-air consumption, plus any simultaneous loads drawing from the same compressor. Ask the dryer manufacturer whether the installation consumes purge air and whether the compressor's stated capacity is already net of that consumption — include any additional demand without counting it twice.

- Pressure loss: tubing, hoses, filters, dryers, and regulation between the compressor and generator. Atlas Copco's compressed-air treatment guidance notes that filtration causes a pressure drop, and that filters should be correctly sized for the system flow rate and replaced on schedule to maintain efficiency.

Where the compressor feeds multiple points, confirm the generator's minimum inlet pressure is maintained during peak simultaneous demand.

Step 5: Confirm duty-cycle suitability and pressure-switch behavior

Confirm the compressor's allowable duty cycle for your intended operating hours. Also confirm that pressure at the generator inlet remains within its required range throughout the compressor's operating cycle, after downstream pressure losses — a cut-in pressure that merely exceeds the generator's minimum is not sufficient if downstream losses consume that margin.

A receiver provides temporary storage to meet short-term peak demands that the compressor cannot meet alone, and Atlas Copco's air receiver guidance notes that stored air is only useful as long as its pressure remains sufficient for the process using it. A larger receiver does not extend sustained production capacity beyond the compressor's rated output.

Step 6: Obtain manufacturer approval for the pairing

Ask the generator or compressor manufacturer to confirm the proposed pairing in writing. Where the manufacturer publishes validated combined-system output, use that figure rather than the generator's standalone maximum.

Worked example: reading the NITRO-GEN tables

Using Organomation's published compressor-specification data:

At the table's listed operating point of 73 psi inlet and 97% purity, Organomation reports 8 L/min nitrogen output and 29.67 L/min feed-air consumption. This is the data you would use as the generator's demand figure in the sizing workflow above.

Whether a specific compressor can meet that requirement with a safe margin depends on several details that published documentation may not fully resolve: whether both figures use the same flow-reference conditions, whether the compressor's rating represents net dry-air delivery after dryer losses, the compressor's continuous-duty rating, and its pressure-switch settings. Treat any preliminary comparison as a screening step, not a confirmed compatibility conclusion — and confirm the pairing with the manufacturer before relying on it.

Can I size the compressor from the nitrogen generator's output flow?

No. A membrane nitrogen generator consumes several times more compressed air than the nitrogen it produces, because oxygen, water vapor, and CO₂ permeate the membrane and are vented rather than collected — the process Organomation describes in its membrane generator overview.

Two data points from Organomation's compressor-specification document illustrate the ratio:

The ratio is not constant — it varies with purity, pressure, and generator design. Size from the generator's feed-air consumption table, never from nitrogen output.

Quick sizing checklist

• [ ] Target nitrogen purity and flow identified.
• [ ] Generator's feed-air consumption at that purity and flow found.
• [ ] Generator's minimum inlet pressure confirmed.
• [ ] Compressor's delivered flow at that pressure confirmed, on comparable reference conditions.
• [ ] Dryer and filtration pressure losses accounted for.
• [ ] Simultaneous loads on the same compressor accounted for.
• [ ] Duty-cycle rating and pressure-switch behavior confirmed.
• [ ] Manufacturer approval for the pairing obtained.
  

Get a sizing assessment

Send us your generator model, required inlet pressure, feed-air consumption at your intended purity and flow, and expected operating hours. We'll confirm whether the W-M57391 or another compressor is the right fit.

FAQs

How much compressed air does a nitrogen generator need?

It depends on the generator's design, target purity, and inlet pressure. Organomation's compressor-specification data shows the NITRO-GEN requiring 19.33 L/min of compressed air to deliver 2.5 L/min of nitrogen at 99% purity, and 29.67 L/min to deliver 8 L/min at 97% purity — several times the nitrogen output. Use your specific generator's published feed-air consumption table rather than a general rule of thumb.

What happens if I undersize the compressor?

The compressor may not be able to hold the generator's minimum inlet pressure while meeting its feed-air demand. Confirm the consequences for your specific generator with the manufacturer rather than assuming a generic outcome.

Do I need a larger receiver tank?

A larger receiver provides storage to meet short-term peak demands, and Atlas Copco's air receiver guidance describes receivers as buffers that help meet short-term peaks the compressor cannot meet alone — but stored air is only useful while its pressure remains sufficient for the application. If your generator's continuous feed-air demand exceeds the compressor's continuous output, a larger tank will not fix it.

How do I convert CFM to L/min?

1 CFM equals approximately 28.32 L/min. Organomation's W-M57391 is rated at 5.47 CFM free-air capacity, which is approximately 155 L/min.